version 1.1, 1994/10/24 19:15:57
|
version 1.44, 1997/03/04 17:49:49
|
Line 1
|
Line 1
|
\input texinfo @c -*-texinfo-*- |
\input texinfo @c -*-texinfo-*- |
@comment The source is gforth.ds, from which gforth.texi is generated |
@comment The source is gforth.ds, from which gforth.texi is generated |
@comment %**start of header (This is for running Texinfo on a region.) |
@comment %**start of header (This is for running Texinfo on a region.) |
@setfilename gforth-info |
@setfilename gforth.info |
@settitle GNU Forth Manual |
@settitle Gforth Manual |
@setchapternewpage odd |
@comment @setchapternewpage odd |
@comment %**end of header (This is for running Texinfo on a region.) |
@comment %**end of header (This is for running Texinfo on a region.) |
|
|
@ifinfo |
@ifinfo |
This file documents GNU Forth 0.0 |
This file documents Gforth 0.3 |
|
|
Copyright @copyright{} 1994 GNU Forth Development Group |
Copyright @copyright{} 1995-1997 Free Software Foundation, Inc. |
|
|
Permission is granted to make and distribute verbatim copies of |
Permission is granted to make and distribute verbatim copies of |
this manual provided the copyright notice and this permission notice |
this manual provided the copyright notice and this permission notice |
are preserved on all copies. |
are preserved on all copies. |
|
|
@ignore |
@ignore |
Permission is granted to process this file through TeX and print the |
Permission is granted to process this file through TeX and print the |
results, provided the printed document carries a copying permission |
results, provided the printed document carries a copying permission |
notice identical to this one except for the removal of this paragraph |
notice identical to this one except for the removal of this paragraph |
(this paragraph not being relevant to the printed manual). |
(this paragraph not being relevant to the printed manual). |
|
|
@end ignore |
@end ignore |
Permission is granted to copy and distribute modified versions of this |
Permission is granted to copy and distribute modified versions of this |
manual under the conditions for verbatim copying, provided also that the |
manual under the conditions for verbatim copying, provided also that the |
sections entitled "Distribution" and "General Public License" are |
sections entitled "Distribution" and "General Public License" are |
Line 36 Copyright @copyright{} 1994 GNU Forth De
|
Line 36 Copyright @copyright{} 1994 GNU Forth De
|
of in the original English. |
of in the original English. |
@end ifinfo |
@end ifinfo |
|
|
|
@finalout |
@titlepage |
@titlepage |
@sp 10 |
@sp 10 |
@center @titlefont{GNU Forth Manual} |
@center @titlefont{Gforth Manual} |
@sp 2 |
@sp 2 |
@center for version 0.0 |
@center for version 0.3 |
@sp 2 |
@sp 2 |
@center Anton Ertl |
@center Anton Ertl |
|
@center Bernd Paysan |
|
@sp 3 |
|
@center This manual is under construction |
|
|
@comment The following two commands start the copyright page. |
@comment The following two commands start the copyright page. |
@page |
@page |
@vskip 0pt plus 1filll |
@vskip 0pt plus 1filll |
Copyright @copyright{} 1994 GNU Forth Development Group |
Copyright @copyright{} 1995--1997 Free Software Foundation, Inc. |
|
|
@comment !! Published by ... or You can get a copy of this manual ... |
@comment !! Published by ... or You can get a copy of this manual ... |
|
|
Line 72 Copyright @copyright{} 1994 GNU Forth De
|
Line 76 Copyright @copyright{} 1994 GNU Forth De
|
|
|
@node Top, License, (dir), (dir) |
@node Top, License, (dir), (dir) |
@ifinfo |
@ifinfo |
GNU Forth is a free implementation of ANS Forth available on many |
Gforth is a free implementation of ANS Forth available on many |
personal machines. This manual corresponds to version 0.0. |
personal machines. This manual corresponds to version 0.3. |
@end ifinfo |
@end ifinfo |
|
|
@menu |
@menu |
* License:: |
* License:: |
* Goals:: About the GNU Forth Project |
* Goals:: About the Gforth Project |
* Other Books:: Things you might want to read |
* Other Books:: Things you might want to read |
* Invocation:: Starting GNU Forth |
* Invoking Gforth:: Starting Gforth |
* Words:: Forth words available in GNU Forth |
* Words:: Forth words available in Gforth |
* ANS conformance:: Implementation-defined options etc. |
* Tools:: Programming tools |
* Model:: The abstract machine of GNU Forth |
* ANS conformance:: Implementation-defined options etc. |
* Emacs and GForth:: The GForth Mode |
* Model:: The abstract machine of Gforth |
* Internals:: Implementation details |
* Integrating Gforth:: Forth as scripting language for applications |
* Bugs:: How to report them |
* Emacs and Gforth:: The Gforth Mode |
* Pedigree:: Ancestors of GNU Forth |
* Image Files:: @code{.fi} files contain compiled code |
* Word Index:: An item for each Forth word |
* Engine:: The inner interpreter and the primitives |
* Node Index:: An item for each node |
* Bugs:: How to report them |
@end menu |
* Origin:: Authors and ancestors of Gforth |
|
* Word Index:: An item for each Forth word |
@node License, Goals, Top, Top |
* Concept Index:: A menu covering many topics |
@unnumbered License |
@end menu |
!! Insert GPL here |
|
|
@node License, Preface, Top, Top |
|
@unnumbered GNU GENERAL PUBLIC LICENSE |
|
@center Version 2, June 1991 |
|
|
|
@display |
|
Copyright @copyright{} 1989, 1991 Free Software Foundation, Inc. |
|
675 Mass Ave, Cambridge, MA 02139, USA |
|
|
|
Everyone is permitted to copy and distribute verbatim copies |
|
of this license document, but changing it is not allowed. |
|
@end display |
|
|
|
@unnumberedsec Preamble |
|
|
|
The licenses for most software are designed to take away your |
|
freedom to share and change it. By contrast, the GNU General Public |
|
License is intended to guarantee your freedom to share and change free |
|
software---to make sure the software is free for all its users. This |
|
General Public License applies to most of the Free Software |
|
Foundation's software and to any other program whose authors commit to |
|
using it. (Some other Free Software Foundation software is covered by |
|
the GNU Library General Public License instead.) You can apply it to |
|
your programs, too. |
|
|
|
When we speak of free software, we are referring to freedom, not |
|
price. Our General Public Licenses are designed to make sure that you |
|
have the freedom to distribute copies of free software (and charge for |
|
this service if you wish), that you receive source code or can get it |
|
if you want it, that you can change the software or use pieces of it |
|
in new free programs; and that you know you can do these things. |
|
|
|
To protect your rights, we need to make restrictions that forbid |
|
anyone to deny you these rights or to ask you to surrender the rights. |
|
These restrictions translate to certain responsibilities for you if you |
|
distribute copies of the software, or if you modify it. |
|
|
|
For example, if you distribute copies of such a program, whether |
|
gratis or for a fee, you must give the recipients all the rights that |
|
you have. You must make sure that they, too, receive or can get the |
|
source code. And you must show them these terms so they know their |
|
rights. |
|
|
|
We protect your rights with two steps: (1) copyright the software, and |
|
(2) offer you this license which gives you legal permission to copy, |
|
distribute and/or modify the software. |
|
|
|
Also, for each author's protection and ours, we want to make certain |
|
that everyone understands that there is no warranty for this free |
|
software. If the software is modified by someone else and passed on, we |
|
want its recipients to know that what they have is not the original, so |
|
that any problems introduced by others will not reflect on the original |
|
authors' reputations. |
|
|
|
Finally, any free program is threatened constantly by software |
|
patents. We wish to avoid the danger that redistributors of a free |
|
program will individually obtain patent licenses, in effect making the |
|
program proprietary. To prevent this, we have made it clear that any |
|
patent must be licensed for everyone's free use or not licensed at all. |
|
|
|
The precise terms and conditions for copying, distribution and |
|
modification follow. |
|
|
|
@iftex |
|
@unnumberedsec TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION |
|
@end iftex |
|
@ifinfo |
|
@center TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION |
|
@end ifinfo |
|
|
|
@enumerate 0 |
|
@item |
|
This License applies to any program or other work which contains |
|
a notice placed by the copyright holder saying it may be distributed |
|
under the terms of this General Public License. The ``Program'', below, |
|
refers to any such program or work, and a ``work based on the Program'' |
|
means either the Program or any derivative work under copyright law: |
|
that is to say, a work containing the Program or a portion of it, |
|
either verbatim or with modifications and/or translated into another |
|
language. (Hereinafter, translation is included without limitation in |
|
the term ``modification''.) Each licensee is addressed as ``you''. |
|
|
|
Activities other than copying, distribution and modification are not |
|
covered by this License; they are outside its scope. The act of |
|
running the Program is not restricted, and the output from the Program |
|
is covered only if its contents constitute a work based on the |
|
Program (independent of having been made by running the Program). |
|
Whether that is true depends on what the Program does. |
|
|
|
@item |
|
You may copy and distribute verbatim copies of the Program's |
|
source code as you receive it, in any medium, provided that you |
|
conspicuously and appropriately publish on each copy an appropriate |
|
copyright notice and disclaimer of warranty; keep intact all the |
|
notices that refer to this License and to the absence of any warranty; |
|
and give any other recipients of the Program a copy of this License |
|
along with the Program. |
|
|
|
You may charge a fee for the physical act of transferring a copy, and |
|
you may at your option offer warranty protection in exchange for a fee. |
|
|
|
@item |
|
You may modify your copy or copies of the Program or any portion |
|
of it, thus forming a work based on the Program, and copy and |
|
distribute such modifications or work under the terms of Section 1 |
|
above, provided that you also meet all of these conditions: |
|
|
|
@enumerate a |
|
@item |
|
You must cause the modified files to carry prominent notices |
|
stating that you changed the files and the date of any change. |
|
|
|
@item |
|
You must cause any work that you distribute or publish, that in |
|
whole or in part contains or is derived from the Program or any |
|
part thereof, to be licensed as a whole at no charge to all third |
|
parties under the terms of this License. |
|
|
|
@item |
|
If the modified program normally reads commands interactively |
|
when run, you must cause it, when started running for such |
|
interactive use in the most ordinary way, to print or display an |
|
announcement including an appropriate copyright notice and a |
|
notice that there is no warranty (or else, saying that you provide |
|
a warranty) and that users may redistribute the program under |
|
these conditions, and telling the user how to view a copy of this |
|
License. (Exception: if the Program itself is interactive but |
|
does not normally print such an announcement, your work based on |
|
the Program is not required to print an announcement.) |
|
@end enumerate |
|
|
|
These requirements apply to the modified work as a whole. If |
|
identifiable sections of that work are not derived from the Program, |
|
and can be reasonably considered independent and separate works in |
|
themselves, then this License, and its terms, do not apply to those |
|
sections when you distribute them as separate works. But when you |
|
distribute the same sections as part of a whole which is a work based |
|
on the Program, the distribution of the whole must be on the terms of |
|
this License, whose permissions for other licensees extend to the |
|
entire whole, and thus to each and every part regardless of who wrote it. |
|
|
|
Thus, it is not the intent of this section to claim rights or contest |
|
your rights to work written entirely by you; rather, the intent is to |
|
exercise the right to control the distribution of derivative or |
|
collective works based on the Program. |
|
|
|
In addition, mere aggregation of another work not based on the Program |
|
with the Program (or with a work based on the Program) on a volume of |
|
a storage or distribution medium does not bring the other work under |
|
the scope of this License. |
|
|
|
@item |
|
You may copy and distribute the Program (or a work based on it, |
|
under Section 2) in object code or executable form under the terms of |
|
Sections 1 and 2 above provided that you also do one of the following: |
|
|
|
@enumerate a |
|
@item |
|
Accompany it with the complete corresponding machine-readable |
|
source code, which must be distributed under the terms of Sections |
|
1 and 2 above on a medium customarily used for software interchange; or, |
|
|
|
@item |
|
Accompany it with a written offer, valid for at least three |
|
years, to give any third party, for a charge no more than your |
|
cost of physically performing source distribution, a complete |
|
machine-readable copy of the corresponding source code, to be |
|
distributed under the terms of Sections 1 and 2 above on a medium |
|
customarily used for software interchange; or, |
|
|
|
@item |
|
Accompany it with the information you received as to the offer |
|
to distribute corresponding source code. (This alternative is |
|
allowed only for noncommercial distribution and only if you |
|
received the program in object code or executable form with such |
|
an offer, in accord with Subsection b above.) |
|
@end enumerate |
|
|
|
The source code for a work means the preferred form of the work for |
|
making modifications to it. For an executable work, complete source |
|
code means all the source code for all modules it contains, plus any |
|
associated interface definition files, plus the scripts used to |
|
control compilation and installation of the executable. However, as a |
|
special exception, the source code distributed need not include |
|
anything that is normally distributed (in either source or binary |
|
form) with the major components (compiler, kernel, and so on) of the |
|
operating system on which the executable runs, unless that component |
|
itself accompanies the executable. |
|
|
|
If distribution of executable or object code is made by offering |
|
access to copy from a designated place, then offering equivalent |
|
access to copy the source code from the same place counts as |
|
distribution of the source code, even though third parties are not |
|
compelled to copy the source along with the object code. |
|
|
|
@item |
|
You may not copy, modify, sublicense, or distribute the Program |
|
except as expressly provided under this License. Any attempt |
|
otherwise to copy, modify, sublicense or distribute the Program is |
|
void, and will automatically terminate your rights under this License. |
|
However, parties who have received copies, or rights, from you under |
|
this License will not have their licenses terminated so long as such |
|
parties remain in full compliance. |
|
|
|
@item |
|
You are not required to accept this License, since you have not |
|
signed it. However, nothing else grants you permission to modify or |
|
distribute the Program or its derivative works. These actions are |
|
prohibited by law if you do not accept this License. Therefore, by |
|
modifying or distributing the Program (or any work based on the |
|
Program), you indicate your acceptance of this License to do so, and |
|
all its terms and conditions for copying, distributing or modifying |
|
the Program or works based on it. |
|
|
|
@item |
|
Each time you redistribute the Program (or any work based on the |
|
Program), the recipient automatically receives a license from the |
|
original licensor to copy, distribute or modify the Program subject to |
|
these terms and conditions. You may not impose any further |
|
restrictions on the recipients' exercise of the rights granted herein. |
|
You are not responsible for enforcing compliance by third parties to |
|
this License. |
|
|
|
@item |
|
If, as a consequence of a court judgment or allegation of patent |
|
infringement or for any other reason (not limited to patent issues), |
|
conditions are imposed on you (whether by court order, agreement or |
|
otherwise) that contradict the conditions of this License, they do not |
|
excuse you from the conditions of this License. If you cannot |
|
distribute so as to satisfy simultaneously your obligations under this |
|
License and any other pertinent obligations, then as a consequence you |
|
may not distribute the Program at all. For example, if a patent |
|
license would not permit royalty-free redistribution of the Program by |
|
all those who receive copies directly or indirectly through you, then |
|
the only way you could satisfy both it and this License would be to |
|
refrain entirely from distribution of the Program. |
|
|
|
If any portion of this section is held invalid or unenforceable under |
|
any particular circumstance, the balance of the section is intended to |
|
apply and the section as a whole is intended to apply in other |
|
circumstances. |
|
|
|
It is not the purpose of this section to induce you to infringe any |
|
patents or other property right claims or to contest validity of any |
|
such claims; this section has the sole purpose of protecting the |
|
integrity of the free software distribution system, which is |
|
implemented by public license practices. Many people have made |
|
generous contributions to the wide range of software distributed |
|
through that system in reliance on consistent application of that |
|
system; it is up to the author/donor to decide if he or she is willing |
|
to distribute software through any other system and a licensee cannot |
|
impose that choice. |
|
|
|
This section is intended to make thoroughly clear what is believed to |
|
be a consequence of the rest of this License. |
|
|
|
@item |
|
If the distribution and/or use of the Program is restricted in |
|
certain countries either by patents or by copyrighted interfaces, the |
|
original copyright holder who places the Program under this License |
|
may add an explicit geographical distribution limitation excluding |
|
those countries, so that distribution is permitted only in or among |
|
countries not thus excluded. In such case, this License incorporates |
|
the limitation as if written in the body of this License. |
|
|
|
@item |
|
The Free Software Foundation may publish revised and/or new versions |
|
of the General Public License from time to time. Such new versions will |
|
be similar in spirit to the present version, but may differ in detail to |
|
address new problems or concerns. |
|
|
|
Each version is given a distinguishing version number. If the Program |
|
specifies a version number of this License which applies to it and ``any |
|
later version'', you have the option of following the terms and conditions |
|
either of that version or of any later version published by the Free |
|
Software Foundation. If the Program does not specify a version number of |
|
this License, you may choose any version ever published by the Free Software |
|
Foundation. |
|
|
|
@item |
|
If you wish to incorporate parts of the Program into other free |
|
programs whose distribution conditions are different, write to the author |
|
to ask for permission. For software which is copyrighted by the Free |
|
Software Foundation, write to the Free Software Foundation; we sometimes |
|
make exceptions for this. Our decision will be guided by the two goals |
|
of preserving the free status of all derivatives of our free software and |
|
of promoting the sharing and reuse of software generally. |
|
|
|
@iftex |
|
@heading NO WARRANTY |
|
@end iftex |
|
@ifinfo |
|
@center NO WARRANTY |
|
@end ifinfo |
|
|
|
@item |
|
BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY |
|
FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN |
|
OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES |
|
PROVIDE THE PROGRAM ``AS IS'' WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED |
|
OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF |
|
MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS |
|
TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE |
|
PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, |
|
REPAIR OR CORRECTION. |
|
|
|
@item |
|
IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING |
|
WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR |
|
REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, |
|
INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING |
|
OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED |
|
TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY |
|
YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER |
|
PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE |
|
POSSIBILITY OF SUCH DAMAGES. |
|
@end enumerate |
|
|
|
@iftex |
|
@heading END OF TERMS AND CONDITIONS |
|
@end iftex |
|
@ifinfo |
|
@center END OF TERMS AND CONDITIONS |
|
@end ifinfo |
|
|
|
@page |
|
@unnumberedsec How to Apply These Terms to Your New Programs |
|
|
|
If you develop a new program, and you want it to be of the greatest |
|
possible use to the public, the best way to achieve this is to make it |
|
free software which everyone can redistribute and change under these terms. |
|
|
|
To do so, attach the following notices to the program. It is safest |
|
to attach them to the start of each source file to most effectively |
|
convey the exclusion of warranty; and each file should have at least |
|
the ``copyright'' line and a pointer to where the full notice is found. |
|
|
|
@smallexample |
|
@var{one line to give the program's name and a brief idea of what it does.} |
|
Copyright (C) 19@var{yy} @var{name of author} |
|
|
|
This program is free software; you can redistribute it and/or modify |
|
it under the terms of the GNU General Public License as published by |
|
the Free Software Foundation; either version 2 of the License, or |
|
(at your option) any later version. |
|
|
|
This program is distributed in the hope that it will be useful, |
|
but WITHOUT ANY WARRANTY; without even the implied warranty of |
|
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
|
GNU General Public License for more details. |
|
|
|
You should have received a copy of the GNU General Public License |
|
along with this program; if not, write to the Free Software |
|
Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. |
|
@end smallexample |
|
|
|
Also add information on how to contact you by electronic and paper mail. |
|
|
|
If the program is interactive, make it output a short notice like this |
|
when it starts in an interactive mode: |
|
|
|
@smallexample |
|
Gnomovision version 69, Copyright (C) 19@var{yy} @var{name of author} |
|
Gnomovision comes with ABSOLUTELY NO WARRANTY; for details |
|
type `show w'. |
|
This is free software, and you are welcome to redistribute it |
|
under certain conditions; type `show c' for details. |
|
@end smallexample |
|
|
|
The hypothetical commands @samp{show w} and @samp{show c} should show |
|
the appropriate parts of the General Public License. Of course, the |
|
commands you use may be called something other than @samp{show w} and |
|
@samp{show c}; they could even be mouse-clicks or menu items---whatever |
|
suits your program. |
|
|
|
You should also get your employer (if you work as a programmer) or your |
|
school, if any, to sign a ``copyright disclaimer'' for the program, if |
|
necessary. Here is a sample; alter the names: |
|
|
|
@smallexample |
|
Yoyodyne, Inc., hereby disclaims all copyright interest in the program |
|
`Gnomovision' (which makes passes at compilers) written by James Hacker. |
|
|
|
@var{signature of Ty Coon}, 1 April 1989 |
|
Ty Coon, President of Vice |
|
@end smallexample |
|
|
|
This General Public License does not permit incorporating your program into |
|
proprietary programs. If your program is a subroutine library, you may |
|
consider it more useful to permit linking proprietary applications with the |
|
library. If this is what you want to do, use the GNU Library General |
|
Public License instead of this License. |
|
|
@iftex |
@iftex |
|
@node Preface, Goals, License, Top |
|
@comment node-name, next, previous, up |
@unnumbered Preface |
@unnumbered Preface |
This manual documents GNU Forth. The reader is expected to know |
@cindex Preface |
|
This manual documents Gforth. The reader is expected to know |
Forth. This manual is primarily a reference manual. @xref{Other Books} |
Forth. This manual is primarily a reference manual. @xref{Other Books} |
for introductory material. |
for introductory material. |
@end iftex |
@end iftex |
|
|
@node Goals, Other Books, License, Top |
@node Goals, Other Books, Preface, Top |
@comment node-name, next, previous, up |
@comment node-name, next, previous, up |
@chapter Goals of GNU Forth |
@chapter Goals of Gforth |
@cindex Goals |
@cindex Goals |
The goal of the GNU Forth Project is to develop a standard model for |
The goal of the Gforth Project is to develop a standard model for |
ANSI Forth. This can be split into several subgoals: |
ANS Forth. This can be split into several subgoals: |
|
|
@itemize @bullet |
@itemize @bullet |
@item |
@item |
GNU Forth should conform to the ANSI Forth standard. |
Gforth should conform to the Forth standard (ANS Forth). |
@item |
@item |
It should be a model, i.e. it should define all the |
It should be a model, i.e. it should define all the |
implementation-dependent things. |
implementation-dependent things. |
Line 121 It should become standard, i.e. widely a
|
Line 519 It should become standard, i.e. widely a
|
is the most difficult one. |
is the most difficult one. |
@end itemize |
@end itemize |
|
|
To achieve these goals GNU Forth should be |
To achieve these goals Gforth should be |
@itemize @bullet |
@itemize @bullet |
@item |
@item |
Similar to previous models (fig-Forth, F83) |
Similar to previous models (fig-Forth, F83) |
Line 137 Free.
|
Line 535 Free.
|
Available on many machines/easy to port. |
Available on many machines/easy to port. |
@end itemize |
@end itemize |
|
|
Have we achieved these goals? GNU Forth conforms to the ANS Forth |
Have we achieved these goals? Gforth conforms to the ANS Forth |
standard; it may be considered a model, but we have not yet documented |
standard. It may be considered a model, but we have not yet documented |
which parts of the model are stable and which parts we are likely to |
which parts of the model are stable and which parts we are likely to |
change; it certainly has not yet become a de facto standard. It has some |
change. It certainly has not yet become a de facto standard. It has some |
similarities and some differences to previous models; It has some |
similarities and some differences to previous models. It has some |
powerful features, but not yet everything that we envisioned; on RISCs |
powerful features, but not yet everything that we envisioned. We |
it is as fast as interpreters programmed in assembly, on |
certainly have achieved our execution speed goals (@pxref{Performance}). |
register-starved machines it is not so fast, but still faster than any |
It is free and available on many machines. |
other C-based interpretive implementation; it is free and available on |
|
many machines. |
|
|
|
@node Other Books, Invocation, Goals, Top |
@node Other Books, Invoking Gforth, Goals, Top |
@chapter Other books on ANS Forth |
@chapter Other books on ANS Forth |
|
@cindex books on Forth |
|
|
As the standard is relatively new, there are not many books out yet. It |
As the standard is relatively new, there are not many books out yet. It |
is not recommended to learn Forth by using GNU Forth and a book that is |
is not recommended to learn Forth by using Gforth and a book that is |
not written for ANS Forth, as you will not know your mistakes from the |
not written for ANS Forth, as you will not know your mistakes from the |
deviations of the book. |
deviations of the book. |
|
|
|
@cindex standard document for ANS Forth |
|
@cindex ANS Forth document |
There is, of course, the standard, the definite reference if you want to |
There is, of course, the standard, the definite reference if you want to |
write ANS Forth programs. It will be available in printed form from |
write ANS Forth programs. It is available in printed form from the |
Global Engineering Documents !! somtime in spring or summer 1994. If you |
National Standards Institute Sales Department (Tel.: USA (212) 642-4900; |
are lucky, you can still get dpANS6 (the draft that was approved as |
Fax.: USA (212) 302-1286) as document @cite{X3.215-1994} for about $200. You |
standard) by aftp from ftp.uu.net:/vendor/minerva/x3j14. |
can also get it from Global Engineering Documents (Tel.: USA (800) |
|
854-7179; Fax.: (303) 843-9880) for about $300. |
@cite{Forth: The new model} by Jack Woehr (!! Publisher) is an |
|
|
@cite{dpANS6}, the last draft of the standard, which was then submitted to ANSI |
|
for publication is available electronically and for free in some MS Word |
|
format, and it has been converted to HTML. Some pointers to these |
|
versions can be found through |
|
@*@file{http://www.complang.tuwien.ac.at/projects/forth.html}. |
|
|
|
@cindex introductory book |
|
@cindex book, introductory |
|
@cindex Woehr, Jack: @cite{Forth: The New Model} |
|
@cindex @cite{Forth: The new model} (book) |
|
@cite{Forth: The New Model} by Jack Woehr (Prentice-Hall, 1993) is an |
introductory book based on a draft version of the standard. It does not |
introductory book based on a draft version of the standard. It does not |
cover the whole standard. It also contains interesting background |
cover the whole standard. It also contains interesting background |
information (Jack Woehr was in the ANS Forth Technical Committe). It is |
information (Jack Woehr was in the ANS Forth Technical Committee). It is |
not appropriate for complete newbies, but programmers experienced in |
not appropriate for complete newbies, but programmers experienced in |
other languages should find it ok. |
other languages should find it ok. |
|
|
@node Invocation, Words, Other Books, Top |
@node Invoking Gforth, Words, Other Books, Top |
@chapter Invocation |
@chapter Invoking Gforth |
|
@cindex invoking Gforth |
|
@cindex running Gforth |
|
@cindex command-line options |
|
@cindex options on the command line |
|
@cindex flags on the command line |
|
|
You will usually just say @code{gforth}. In many other cases the default |
You will usually just say @code{gforth}. In many other cases the default |
GNU Forth image will be invoked like this: |
Gforth image will be invoked like this: |
|
|
@example |
@example |
gforth [files] [-e forth-code] |
gforth [files] [-e forth-code] |
Line 192 The initialization options must come bef
|
Line 607 The initialization options must come bef
|
line. They are: |
line. They are: |
|
|
@table @code |
@table @code |
|
@cindex -i, command-line option |
|
@cindex --image-file, command-line option |
@item --image-file @var{file} |
@item --image-file @var{file} |
|
@itemx -i @var{file} |
Loads the Forth image @var{file} instead of the default |
Loads the Forth image @var{file} instead of the default |
@file{gforth.fi}. |
@file{gforth.fi} (@pxref{Image Files}). |
|
|
|
@cindex --path, command-line option |
|
@cindex -p, command-line option |
@item --path @var{path} |
@item --path @var{path} |
Uses @var{path} for searching the image file and Forth source code |
@itemx -p @var{path} |
files instead of the default in the environment variable |
Uses @var{path} for searching the image file and Forth source code files |
@code{GFORTHPATH} or the path specified at installation time (typically |
instead of the default in the environment variable @code{GFORTHPATH} or |
@file{/usr/local/lib/gforth:.}). A path is given as a @code{:}-separated |
the path specified at installation time (e.g., |
list. |
@file{/usr/local/share/gforth/0.2.0:.}). A path is given as a list of |
|
directories, separated by @samp{:} (on Unix) or @samp{;} (on other OSs). |
|
|
|
@cindex --dictionary-size, command-line option |
|
@cindex -m, command-line option |
|
@cindex @var{size} parameters for command-line options |
|
@cindex size of the dictionary and the stacks |
@item --dictionary-size @var{size} |
@item --dictionary-size @var{size} |
@item -m @var{size} |
@itemx -m @var{size} |
Allocate @var{size} space for the Forth dictionary space instead of |
Allocate @var{size} space for the Forth dictionary space instead of |
using the default specified in the image (typically 256K). The |
using the default specified in the image (typically 256K). The |
@var{size} specification consists of an integer and a unit (e.g., |
@var{size} specification consists of an integer and a unit (e.g., |
Line 212 using the default specified in the image
|
Line 637 using the default specified in the image
|
size, in this case Cells), @code{k} (kilobytes), and @code{M} |
size, in this case Cells), @code{k} (kilobytes), and @code{M} |
(Megabytes). If no unit is specified, @code{e} is used. |
(Megabytes). If no unit is specified, @code{e} is used. |
|
|
|
@cindex --data-stack-size, command-line option |
|
@cindex -d, command-line option |
@item --data-stack-size @var{size} |
@item --data-stack-size @var{size} |
@item -d @var{size} |
@itemx -d @var{size} |
Allocate @var{size} space for the data stack instead of using the |
Allocate @var{size} space for the data stack instead of using the |
default specified in the image (typically 16K). |
default specified in the image (typically 16K). |
|
|
|
@cindex --return-stack-size, command-line option |
|
@cindex -r, command-line option |
@item --return-stack-size @var{size} |
@item --return-stack-size @var{size} |
@item -r @var{size} |
@itemx -r @var{size} |
Allocate @var{size} space for the return stack instead of using the |
Allocate @var{size} space for the return stack instead of using the |
default specified in the image (typically 16K). |
default specified in the image (typically 15K). |
|
|
|
@cindex --fp-stack-size, command-line option |
|
@cindex -f, command-line option |
@item --fp-stack-size @var{size} |
@item --fp-stack-size @var{size} |
@item -f @var{size} |
@itemx -f @var{size} |
Allocate @var{size} space for the floating point stack instead of |
Allocate @var{size} space for the floating point stack instead of |
using the default specified in the image (typically 16K). In this case |
using the default specified in the image (typically 15.5K). In this case |
the unit specifier @code{e} refers to floating point numbers. |
the unit specifier @code{e} refers to floating point numbers. |
|
|
|
@cindex --locals-stack-size, command-line option |
|
@cindex -l, command-line option |
@item --locals-stack-size @var{size} |
@item --locals-stack-size @var{size} |
@item -l @var{size} |
@itemx -l @var{size} |
Allocate @var{size} space for the locals stack instead of using the |
Allocate @var{size} space for the locals stack instead of using the |
default specified in the image (typically 16K). |
default specified in the image (typically 14.5K). |
|
|
|
@cindex -h, command-line option |
|
@cindex --help, command-line option |
|
@item --help |
|
@itemx -h |
|
Print a message about the command-line options |
|
|
|
@cindex -v, command-line option |
|
@cindex --version, command-line option |
|
@item --version |
|
@itemx -v |
|
Print version and exit |
|
|
|
@cindex --debug, command-line option |
|
@item --debug |
|
Print some information useful for debugging on startup. |
|
|
|
@cindex --offset-image, command-line option |
|
@item --offset-image |
|
Start the dictionary at a slightly different position than would be used |
|
otherwise (useful for creating data-relocatable images, |
|
@pxref{Data-Relocatable Image Files}). |
|
|
|
@cindex --clear-dictionary, command-line option |
|
@item --clear-dictionary |
|
Initialize all bytes in the dictionary to 0 before loading the image |
|
(@pxref{Data-Relocatable Image Files}). |
@end table |
@end table |
|
|
|
@cindex loading files at startup |
|
@cindex executing code on startup |
|
@cindex batch processing with Gforth |
As explained above, the image-specific command-line arguments for the |
As explained above, the image-specific command-line arguments for the |
default image @file{gforth.fi} consist of a sequence of filenames and |
default image @file{gforth.fi} consist of a sequence of filenames and |
@code{-e @var{forth-code}} options that are interpreted in the seqence |
@code{-e @var{forth-code}} options that are interpreted in the sequence |
in which they are given. The @code{-e @var{forth-code}} or |
in which they are given. The @code{-e @var{forth-code}} or |
@code{--evaluate @var{forth-code}} option evaluates the forth |
@code{--evaluate @var{forth-code}} option evaluates the forth |
code. This option takes only one argument; if you want to evaluate more |
code. This option takes only one argument; if you want to evaluate more |
Line 245 Forth words, you have to quote them or u
|
Line 707 Forth words, you have to quote them or u
|
after processing the command line (instead of entering interactive mode) |
after processing the command line (instead of entering interactive mode) |
append @code{-e bye} to the command line. |
append @code{-e bye} to the command line. |
|
|
|
@cindex versions, invoking other versions of Gforth |
|
If you have several versions of Gforth installed, @code{gforth} will |
|
invoke the version that was installed last. @code{gforth-@var{version}} |
|
invokes a specific version. You may want to use the option |
|
@code{--path}, if your environment contains the variable |
|
@code{GFORTHPATH}. |
|
|
Not yet implemented: |
Not yet implemented: |
On startup the system first executes the system initialization file |
On startup the system first executes the system initialization file |
(unless the option @code{--no-init-file} is given; note that the system |
(unless the option @code{--no-init-file} is given; note that the system |
Line 253 the user initialization file @file{.gfor
|
Line 722 the user initialization file @file{.gfor
|
option @code{--no-rc} is given; this file is first searched in @file{.}, |
option @code{--no-rc} is given; this file is first searched in @file{.}, |
then in @file{~}, then in the normal path (see above). |
then in @file{~}, then in the normal path (see above). |
|
|
@node Words, , Invocation, Top |
@node Words, Tools, Invoking Gforth, Top |
@chapter Forth Words |
@chapter Forth Words |
|
@cindex Words |
|
|
@menu |
@menu |
* Notation:: |
* Notation:: |
* Arithmetic:: |
* Arithmetic:: |
* Stack Manipulation:: |
* Stack Manipulation:: |
* Memory access:: |
* Memory:: |
* Control Structures:: |
* Control Structures:: |
* Local Variables:: |
* Locals:: |
* Defining Words:: |
* Defining Words:: |
* Vocabularies:: |
* Tokens for Words:: |
* Files:: |
* Wordlists:: |
* Blocks:: |
* Files:: |
* Other I/O:: |
* Blocks:: |
* Programming Tools:: |
* Other I/O:: |
|
* Programming Tools:: |
|
* Assembler and Code words:: |
|
* Threading Words:: |
@end menu |
@end menu |
|
|
@node Notation, Arithmetic, Words, Words |
@node Notation, Arithmetic, Words, Words |
@section Notation |
@section Notation |
|
@cindex notation of glossary entries |
|
@cindex format of glossary entries |
|
@cindex glossary notation format |
|
@cindex word glossary entry format |
|
|
The Forth words are described in this section in the glossary notation |
The Forth words are described in this section in the glossary notation |
that has become a de-facto standard for Forth texts, i.e. |
that has become a de-facto standard for Forth texts, i.e., |
|
|
@quotation |
@format |
@var{word} @var{Stack effect} @var{wordset} @var{pronunciation} |
@var{word} @var{Stack effect} @var{wordset} @var{pronunciation} |
|
@end format |
@var{Description} |
@var{Description} |
@end quotation |
|
|
|
@table @var |
@table @var |
@item word |
@item word |
The name of the word. BTW, GNU Forth is case insensitive, so you can |
@cindex case insensitivity |
type the words in in lower case. |
The name of the word. BTW, Gforth is case insensitive, so you can |
|
type the words in in lower case (However, @pxref{core-idef}). |
|
|
@item Stack effect |
@item Stack effect |
|
@cindex stack effect |
The stack effect is written in the notation @code{@var{before} -- |
The stack effect is written in the notation @code{@var{before} -- |
@var{after}}, where @var{before} and @var{after} describe the top of |
@var{after}}, where @var{before} and @var{after} describe the top of |
stack entries before and after the execution of the word. The rest of |
stack entries before and after the execution of the word. The rest of |
the stack is not touched by the word. The top of stack is rightmost, |
the stack is not touched by the word. The top of stack is rightmost, |
i.e., a stack sequence is written as it is typed in. Note that GNU Forth |
i.e., a stack sequence is written as it is typed in. Note that Gforth |
uses a separate floating point stack, but a unified stack |
uses a separate floating point stack, but a unified stack |
notation. Also, return stack effects are not shown in @var{stack |
notation. Also, return stack effects are not shown in @var{stack |
effect}, but in @var{Description}. The name of a stack item describes |
effect}, but in @var{Description}. The name of a stack item describes |
the type and/or the function of the item. See below for a discussion of |
the type and/or the function of the item. See below for a discussion of |
the types. |
the types. |
|
|
|
All words have two stack effects: A compile-time stack effect and a |
|
run-time stack effect. The compile-time stack-effect of most words is |
|
@var{ -- }. If the compile-time stack-effect of a word deviates from |
|
this standard behaviour, or the word does other unusual things at |
|
compile time, both stack effects are shown; otherwise only the run-time |
|
stack effect is shown. |
|
|
|
@cindex pronounciation of words |
@item pronunciation |
@item pronunciation |
How the word is pronounced |
How the word is pronounced. |
|
|
|
@cindex wordset |
@item wordset |
@item wordset |
The ANS Forth standard is divided into several wordsets. A standard |
The ANS Forth standard is divided into several wordsets. A standard |
system need not support all of them. So, the fewer wordsets your program |
system need not support all of them. So, the fewer wordsets your program |
uses the more portable it will be in theory. However, we suspect that |
uses the more portable it will be in theory. However, we suspect that |
most ANS Forth systems on personal machines will feature all |
most ANS Forth systems on personal machines will feature all |
wordsets. Words that are not defined in the ANS standard have |
wordsets. Words that are not defined in the ANS standard have |
@code{gforth} as wordset. |
@code{gforth} or @code{gforth-internal} as wordset. @code{gforth} |
|
describes words that will work in future releases of Gforth; |
|
@code{gforth-internal} words are more volatile. Environmental query |
|
strings are also displayed like words; you can recognize them by the |
|
@code{environment} in the wordset field. |
|
|
@item Description |
@item Description |
A description of the behaviour of the word. |
A description of the behaviour of the word. |
@end table |
@end table |
|
|
The name of a stack item corresponds in the following way with its type: |
@cindex types of stack items |
|
@cindex stack item types |
|
The type of a stack item is specified by the character(s) the name |
|
starts with: |
|
|
@table @code |
@table @code |
@item name starts with |
|
Type |
|
@item f |
@item f |
Bool, i.e. @code{false} or @code{true}. |
@cindex @code{f}, stack item type |
|
Boolean flags, i.e. @code{false} or @code{true}. |
@item c |
@item c |
|
@cindex @code{c}, stack item type |
Char |
Char |
@item w |
@item w |
|
@cindex @code{w}, stack item type |
Cell, can contain an integer or an address |
Cell, can contain an integer or an address |
@item n |
@item n |
|
@cindex @code{n}, stack item type |
signed integer |
signed integer |
@item u |
@item u |
|
@cindex @code{u}, stack item type |
unsigned integer |
unsigned integer |
@item d |
@item d |
|
@cindex @code{d}, stack item type |
double sized signed integer |
double sized signed integer |
@item ud |
@item ud |
|
@cindex @code{ud}, stack item type |
double sized unsigned integer |
double sized unsigned integer |
@item r |
@item r |
Float |
@cindex @code{r}, stack item type |
|
Float (on the FP stack) |
@item a_ |
@item a_ |
|
@cindex @code{a_}, stack item type |
Cell-aligned address |
Cell-aligned address |
@item c_ |
@item c_ |
Char-aligned address (note that a Char is two bytes in Windows NT) |
@cindex @code{c_}, stack item type |
|
Char-aligned address (note that a Char may have two bytes in Windows NT) |
@item f_ |
@item f_ |
|
@cindex @code{f_}, stack item type |
Float-aligned address |
Float-aligned address |
@item df_ |
@item df_ |
|
@cindex @code{df_}, stack item type |
Address aligned for IEEE double precision float |
Address aligned for IEEE double precision float |
@item sf_ |
@item sf_ |
|
@cindex @code{sf_}, stack item type |
Address aligned for IEEE single precision float |
Address aligned for IEEE single precision float |
@item xt |
@item xt |
|
@cindex @code{xt}, stack item type |
Execution token, same size as Cell |
Execution token, same size as Cell |
@item wid |
@item wid |
|
@cindex @code{wid}, stack item type |
Wordlist ID, same size as Cell |
Wordlist ID, same size as Cell |
@item f83name |
@item f83name |
|
@cindex @code{f83name}, stack item type |
Pointer to a name structure |
Pointer to a name structure |
|
@item " |
|
@cindex @code{"}, stack item type |
|
string in the input stream (not the stack). The terminating character is |
|
a blank by default. If it is not a blank, it is shown in @code{<>} |
|
quotes. |
@end table |
@end table |
|
|
@node Arithmetic, , Notation, Words |
@node Arithmetic, Stack Manipulation, Notation, Words |
@section Arithmetic |
@section Arithmetic |
|
@cindex arithmetic words |
|
|
|
@cindex division with potentially negative operands |
Forth arithmetic is not checked, i.e., you will not hear about integer |
Forth arithmetic is not checked, i.e., you will not hear about integer |
overflow on addition or multiplication, you may hear about division by |
overflow on addition or multiplication, you may hear about division by |
zero if you are lucky. The operator is written after the operands, but |
zero if you are lucky. The operator is written after the operands, but |
Line 363 corresponds to @code{2 1 -}. Forth offer
|
Line 880 corresponds to @code{2 1 -}. Forth offer
|
operators. If you perform division with potentially negative operands, |
operators. If you perform division with potentially negative operands, |
you do not want to use @code{/} or @code{/mod} with its undefined |
you do not want to use @code{/} or @code{/mod} with its undefined |
behaviour, but rather @code{fm/mod} or @code{sm/mod} (probably the |
behaviour, but rather @code{fm/mod} or @code{sm/mod} (probably the |
former). |
former, @pxref{Mixed precision}). |
|
|
|
@menu |
|
* Single precision:: |
|
* Bitwise operations:: |
|
* Mixed precision:: operations with single and double-cell integers |
|
* Double precision:: Double-cell integer arithmetic |
|
* Floating Point:: |
|
@end menu |
|
|
|
@node Single precision, Bitwise operations, Arithmetic, Arithmetic |
@subsection Single precision |
@subsection Single precision |
|
@cindex single precision arithmetic words |
|
|
doc-+ |
doc-+ |
doc-- |
doc-- |
doc-* |
doc-* |
Line 377 doc-abs
|
Line 905 doc-abs
|
doc-min |
doc-min |
doc-max |
doc-max |
|
|
|
@node Bitwise operations, Mixed precision, Single precision, Arithmetic |
@subsection Bitwise operations |
@subsection Bitwise operations |
|
@cindex bitwise operation words |
|
|
doc-and |
doc-and |
doc-or |
doc-or |
doc-xor |
doc-xor |
Line 385 doc-invert
|
Line 916 doc-invert
|
doc-2* |
doc-2* |
doc-2/ |
doc-2/ |
|
|
|
@node Mixed precision, Double precision, Bitwise operations, Arithmetic |
@subsection Mixed precision |
@subsection Mixed precision |
|
@cindex mixed precision arithmetic words |
|
|
doc-m+ |
doc-m+ |
doc-*/ |
doc-*/ |
doc-*/mod |
doc-*/mod |
Line 396 doc-um/mod
|
Line 930 doc-um/mod
|
doc-fm/mod |
doc-fm/mod |
doc-sm/rem |
doc-sm/rem |
|
|
|
@node Double precision, Floating Point, Mixed precision, Arithmetic |
@subsection Double precision |
@subsection Double precision |
|
@cindex double precision arithmetic words |
|
|
|
@cindex double-cell numbers, input format |
|
@cindex input format for double-cell numbers |
|
The outer (aka text) interpreter converts numbers containing a dot into |
|
a double precision number. Note that only numbers with the dot as last |
|
character are standard-conforming. |
|
|
doc-d+ |
doc-d+ |
doc-d- |
doc-d- |
doc-dnegate |
doc-dnegate |
Line 404 doc-dabs
|
Line 947 doc-dabs
|
doc-dmin |
doc-dmin |
doc-dmax |
doc-dmax |
|
|
@node Stack Manipulation,,, |
@node Floating Point, , Double precision, Arithmetic |
|
@subsection Floating Point |
|
@cindex floating point arithmetic words |
|
|
|
@cindex floating-point numbers, input format |
|
@cindex input format for floating-point numbers |
|
The format of floating point numbers recognized by the outer (aka text) |
|
interpreter is: a signed decimal number, possibly containing a decimal |
|
point (@code{.}), followed by @code{E} or @code{e}, optionally followed |
|
by a signed integer (the exponent). E.g., @code{1e} is the same as |
|
@code{+1.0e+0}. Note that a number without @code{e} |
|
is not interpreted as floating-point number, but as double (if the |
|
number contains a @code{.}) or single precision integer. Also, |
|
conversions between string and floating point numbers always use base |
|
10, irrespective of the value of @code{BASE}. If @code{BASE} contains a |
|
value greater then 14, the @code{E} may be interpreted as digit and the |
|
number will be interpreted as integer, unless it has a signed exponent |
|
(both @code{+} and @code{-} are allowed as signs). |
|
|
|
@cindex angles in trigonometric operations |
|
@cindex trigonometric operations |
|
Angles in floating point operations are given in radians (a full circle |
|
has 2 pi radians). Note, that Gforth has a separate floating point |
|
stack, but we use the unified notation. |
|
|
|
@cindex floating-point arithmetic, pitfalls |
|
Floating point numbers have a number of unpleasant surprises for the |
|
unwary (e.g., floating point addition is not associative) and even a few |
|
for the wary. You should not use them unless you know what you are doing |
|
or you don't care that the results you get are totally bogus. If you |
|
want to learn about the problems of floating point numbers (and how to |
|
avoid them), you might start with @cite{David Goldberg, What Every |
|
Computer Scientist Should Know About Floating-Point Arithmetic, ACM |
|
Computing Surveys 23(1):5@minus{}48, March 1991}. |
|
|
|
doc-f+ |
|
doc-f- |
|
doc-f* |
|
doc-f/ |
|
doc-fnegate |
|
doc-fabs |
|
doc-fmax |
|
doc-fmin |
|
doc-floor |
|
doc-fround |
|
doc-f** |
|
doc-fsqrt |
|
doc-fexp |
|
doc-fexpm1 |
|
doc-fln |
|
doc-flnp1 |
|
doc-flog |
|
doc-falog |
|
doc-fsin |
|
doc-fcos |
|
doc-fsincos |
|
doc-ftan |
|
doc-fasin |
|
doc-facos |
|
doc-fatan |
|
doc-fatan2 |
|
doc-fsinh |
|
doc-fcosh |
|
doc-ftanh |
|
doc-fasinh |
|
doc-facosh |
|
doc-fatanh |
|
|
|
@node Stack Manipulation, Memory, Arithmetic, Words |
@section Stack Manipulation |
@section Stack Manipulation |
|
@cindex stack manipulation words |
|
|
gforth has a data stack (aka parameter stack) for characters, cells, |
@cindex floating-point stack in the standard |
|
Gforth has a data stack (aka parameter stack) for characters, cells, |
addresses, and double cells, a floating point stack for floating point |
addresses, and double cells, a floating point stack for floating point |
numbers, a return stack for storing the return addresses of colon |
numbers, a return stack for storing the return addresses of colon |
definitions and other data, and a locals stack for storing local |
definitions and other data, and a locals stack for storing local |
Line 417 theoretically keep floating point number
|
Line 1030 theoretically keep floating point number
|
additional difficulty, you don't know how many cells a floating point |
additional difficulty, you don't know how many cells a floating point |
number takes. It is reportedly possible to write words in a way that |
number takes. It is reportedly possible to write words in a way that |
they work also for a unified stack model, but we do not recommend trying |
they work also for a unified stack model, but we do not recommend trying |
it. Also, a Forth system is allowed to keep the local variables on the |
it. Instead, just say that your program has an environmental dependency |
|
on a separate FP stack. |
|
|
|
@cindex return stack and locals |
|
@cindex locals and return stack |
|
Also, a Forth system is allowed to keep the local variables on the |
return stack. This is reasonable, as local variables usually eliminate |
return stack. This is reasonable, as local variables usually eliminate |
the need to use the return stack explicitly. So, if you want to produce |
the need to use the return stack explicitly. So, if you want to produce |
a standard complying program and if you are using local variables in a |
a standard complying program and if you are using local variables in a |
word, forget about return stack manipulations in that word (see the |
word, forget about return stack manipulations in that word (see the |
standard document for the exact rules). |
standard document for the exact rules). |
|
|
|
@menu |
|
* Data stack:: |
|
* Floating point stack:: |
|
* Return stack:: |
|
* Locals stack:: |
|
* Stack pointer manipulation:: |
|
@end menu |
|
|
|
@node Data stack, Floating point stack, Stack Manipulation, Stack Manipulation |
@subsection Data stack |
@subsection Data stack |
|
@cindex data stack manipulation words |
|
@cindex stack manipulations words, data stack |
|
|
doc-drop |
doc-drop |
doc-nip |
doc-nip |
doc-dup |
doc-dup |
Line 444 doc-2tuck
|
Line 1074 doc-2tuck
|
doc-2swap |
doc-2swap |
doc-2rot |
doc-2rot |
|
|
|
@node Floating point stack, Return stack, Data stack, Stack Manipulation |
@subsection Floating point stack |
@subsection Floating point stack |
|
@cindex floating-point stack manipulation words |
|
@cindex stack manipulation words, floating-point stack |
|
|
doc-fdrop |
doc-fdrop |
doc-fnip |
doc-fnip |
doc-fdup |
doc-fdup |
Line 453 doc-ftuck
|
Line 1087 doc-ftuck
|
doc-fswap |
doc-fswap |
doc-frot |
doc-frot |
|
|
|
@node Return stack, Locals stack, Floating point stack, Stack Manipulation |
@subsection Return stack |
@subsection Return stack |
|
@cindex return stack manipulation words |
|
@cindex stack manipulation words, return stack |
|
|
doc->r |
doc->r |
doc-r> |
doc-r> |
doc-r@ |
doc-r@ |
Line 463 doc-2r>
|
Line 1101 doc-2r>
|
doc-2r@ |
doc-2r@ |
doc-2rdrop |
doc-2rdrop |
|
|
|
@node Locals stack, Stack pointer manipulation, Return stack, Stack Manipulation |
@subsection Locals stack |
@subsection Locals stack |
|
|
|
@node Stack pointer manipulation, , Locals stack, Stack Manipulation |
@subsection Stack pointer manipulation |
@subsection Stack pointer manipulation |
|
@cindex stack pointer manipulation words |
|
|
doc-sp@ |
doc-sp@ |
doc-sp! |
doc-sp! |
doc-fp@ |
doc-fp@ |
Line 475 doc-rp!
|
Line 1117 doc-rp!
|
doc-lp@ |
doc-lp@ |
doc-lp! |
doc-lp! |
|
|
@node Memory access |
@node Memory, Control Structures, Stack Manipulation, Words |
@section Memory access |
@section Memory |
|
@cindex Memory words |
|
|
@subsection Stack-Memory transfers |
@menu |
|
* Memory Access:: |
|
* Address arithmetic:: |
|
* Memory Blocks:: |
|
@end menu |
|
|
|
@node Memory Access, Address arithmetic, Memory, Memory |
|
@subsection Memory Access |
|
@cindex memory access words |
|
|
doc-@ |
doc-@ |
doc-! |
doc-! |
Line 494 doc-sf!
|
Line 1145 doc-sf!
|
doc-df@ |
doc-df@ |
doc-df! |
doc-df! |
|
|
|
@node Address arithmetic, Memory Blocks, Memory Access, Memory |
@subsection Address arithmetic |
@subsection Address arithmetic |
|
@cindex address arithmetic words |
|
|
ANS Forth does not specify the sizes of the data types. Instead, it |
ANS Forth does not specify the sizes of the data types. Instead, it |
offers a number of words for computing sizes and doing address |
offers a number of words for computing sizes and doing address |
Line 503 address units (aus); on most systems the
|
Line 1156 address units (aus); on most systems the
|
that a character may have more than one au, so @code{chars} is no noop |
that a character may have more than one au, so @code{chars} is no noop |
(on systems where it is a noop, it compiles to nothing). |
(on systems where it is a noop, it compiles to nothing). |
|
|
|
@cindex alignment of addresses for types |
ANS Forth also defines words for aligning addresses for specific |
ANS Forth also defines words for aligning addresses for specific |
addresses. Many computers require that accesses to specific data types |
types. Many computers require that accesses to specific data types |
must only occur at specific addresses; e.g., that cells may only be |
must only occur at specific addresses; e.g., that cells may only be |
accessed at addresses divisible by 4. Even if a machine allows unaligned |
accessed at addresses divisible by 4. Even if a machine allows unaligned |
accesses, it can usually perform aligned accesses faster. |
accesses, it can usually perform aligned accesses faster. |
|
|
For the performance-concious: alignment operations are usually only |
For the performance-conscious: alignment operations are usually only |
necessary during the definition of a data structure, not during the |
necessary during the definition of a data structure, not during the |
(more frequent) accesses to it. |
(more frequent) accesses to it. |
|
|
Line 518 an oversight, but reflects the fact that
|
Line 1172 an oversight, but reflects the fact that
|
char-aligned have no use in the standard and therefore will not be |
char-aligned have no use in the standard and therefore will not be |
created. |
created. |
|
|
|
@cindex @code{CREATE} and alignment |
The standard guarantees that addresses returned by @code{CREATE}d words |
The standard guarantees that addresses returned by @code{CREATE}d words |
are cell-aligned; in addition, gforth guarantees that these addresses |
are cell-aligned; in addition, Gforth guarantees that these addresses |
are aligned for all purposes. |
are aligned for all purposes. |
|
|
|
Note that the standard defines a word @code{char}, which has nothing to |
|
do with address arithmetic. |
|
|
doc-chars |
doc-chars |
doc-char+ |
doc-char+ |
doc-cells |
doc-cells |
doc-cell+ |
doc-cell+ |
|
doc-cell |
doc-align |
doc-align |
doc-aligned |
doc-aligned |
doc-floats |
doc-floats |
doc-float+ |
doc-float+ |
|
doc-float |
doc-falign |
doc-falign |
doc-faligned |
doc-faligned |
doc-sfloats |
doc-sfloats |
Line 540 doc-dfloats
|
Line 1200 doc-dfloats
|
doc-dfloat+ |
doc-dfloat+ |
doc-dfalign |
doc-dfalign |
doc-dfaligned |
doc-dfaligned |
|
doc-maxalign |
|
doc-maxaligned |
|
doc-cfalign |
|
doc-cfaligned |
doc-address-unit-bits |
doc-address-unit-bits |
|
|
@subsection Memory block access |
@node Memory Blocks, , Address arithmetic, Memory |
|
@subsection Memory Blocks |
|
@cindex memory block words |
|
|
doc-move |
doc-move |
doc-erase |
doc-erase |
Line 555 doc-cmove>
|
Line 1221 doc-cmove>
|
doc-fill |
doc-fill |
doc-blank |
doc-blank |
|
|
@node Control Structures |
@node Control Structures, Locals, Memory, Words |
@section Control Structures |
@section Control Structures |
|
@cindex control structures |
|
|
Control structures in Forth cannot be used in interpret state, only in |
Control structures in Forth cannot be used in interpret state, only in |
compile state, i.e., in a colon definition. We do not like this |
compile state@footnote{More precisely, they have no interpretation |
limitation, but have not seen a satisfying way around it yet, although |
semantics (@pxref{Interpretation and Compilation Semantics})}, i.e., in |
many schemes have been proposed. |
a colon definition. We do not like this limitation, but have not seen a |
|
satisfying way around it yet, although many schemes have been proposed. |
|
|
|
@menu |
|
* Selection:: |
|
* Simple Loops:: |
|
* Counted Loops:: |
|
* Arbitrary control structures:: |
|
* Calls and returns:: |
|
* Exception Handling:: |
|
@end menu |
|
|
|
@node Selection, Simple Loops, Control Structures, Control Structures |
@subsection Selection |
@subsection Selection |
|
@cindex selection control structures |
|
@cindex control structures for selection |
|
|
|
@cindex @code{IF} control structure |
@example |
@example |
@var{flag} |
@var{flag} |
IF |
IF |
Line 581 ELSE
|
Line 1262 ELSE
|
ENDIF |
ENDIF |
@end example |
@end example |
|
|
You can use @code{THEN} instead of {ENDIF}. Indeed, @code{THEN} is |
You can use @code{THEN} instead of @code{ENDIF}. Indeed, @code{THEN} is |
standard, and @code{ENDIF} is not, although it is quite popular. We |
standard, and @code{ENDIF} is not, although it is quite popular. We |
recommend using @code{ENDIF}, because it is less confusing for people |
recommend using @code{ENDIF}, because it is less confusing for people |
who also know other languages (and is not prone to reinforcing negative |
who also know other languages (and is not prone to reinforcing negative |
Line 600 system that only supplies @code{THEN} is
|
Line 1281 system that only supplies @code{THEN} is
|
Forth's @code{THEN} has the meaning 2b, whereas @code{THEN} in Pascal |
Forth's @code{THEN} has the meaning 2b, whereas @code{THEN} in Pascal |
and many other programming languages has the meaning 3d.] |
and many other programming languages has the meaning 3d.] |
|
|
We also provide the words @code{?dup-if} and @code{?dup-0=-if}, so you |
Gforth also provides the words @code{?dup-if} and @code{?dup-0=-if}, so |
can avoid using @code{?dup}. |
you can avoid using @code{?dup}. Using these alternatives is also more |
|
efficient than using @code{?dup}. Definitions in plain standard Forth |
|
for @code{ENDIF}, @code{?DUP-IF} and @code{?DUP-0=-IF} are provided in |
|
@file{compat/control.fs}. |
|
|
|
@cindex @code{CASE} control structure |
@example |
@example |
@var{n} |
@var{n} |
CASE |
CASE |
@var{n1} OF @var{code1} ENDOF |
@var{n1} OF @var{code1} ENDOF |
@var{n2} OF @var{code2} ENDOF |
@var{n2} OF @var{code2} ENDOF |
@dots |
@dots{} |
ENDCASE |
ENDCASE |
@end example |
@end example |
|
|
Line 617 Executes the first @var{codei}, where th
|
Line 1302 Executes the first @var{codei}, where th
|
the last @code{ENDOF}. It may use @var{n}, which is on top of the stack, |
the last @code{ENDOF}. It may use @var{n}, which is on top of the stack, |
but must not consume it. |
but must not consume it. |
|
|
|
@node Simple Loops, Counted Loops, Selection, Control Structures |
@subsection Simple Loops |
@subsection Simple Loops |
|
@cindex simple loops |
|
@cindex loops without count |
|
|
|
@cindex @code{WHILE} loop |
@example |
@example |
BEGIN |
BEGIN |
@var{code1} |
@var{code1} |
Line 629 REPEAT
|
Line 1318 REPEAT
|
@end example |
@end example |
|
|
@var{code1} is executed and @var{flag} is computed. If it is true, |
@var{code1} is executed and @var{flag} is computed. If it is true, |
@var{code2} is executed and the loop is restarted; If @var{flag} is false, execution continues after the @code{REPEAT}. |
@var{code2} is executed and the loop is restarted; If @var{flag} is |
|
false, execution continues after the @code{REPEAT}. |
|
|
|
@cindex @code{UNTIL} loop |
@example |
@example |
BEGIN |
BEGIN |
@var{code} |
@var{code} |
Line 640 UNTIL
|
Line 1331 UNTIL
|
|
|
@var{code} is executed. The loop is restarted if @code{flag} is false. |
@var{code} is executed. The loop is restarted if @code{flag} is false. |
|
|
|
@cindex endless loop |
|
@cindex loops, endless |
@example |
@example |
BEGIN |
BEGIN |
@var{code} |
@var{code} |
Line 648 AGAIN
|
Line 1341 AGAIN
|
|
|
This is an endless loop. |
This is an endless loop. |
|
|
|
@node Counted Loops, Arbitrary control structures, Simple Loops, Control Structures |
@subsection Counted Loops |
@subsection Counted Loops |
|
@cindex counted loops |
|
@cindex loops, counted |
|
@cindex @code{DO} loops |
|
|
The basic counted loop is: |
The basic counted loop is: |
@example |
@example |
Line 685 There are several variations on the coun
|
Line 1382 There are several variations on the coun
|
|
|
@code{LEAVE} leaves the innermost counted loop immediately. |
@code{LEAVE} leaves the innermost counted loop immediately. |
|
|
|
If @var{start} is greater than @var{limit}, a @code{?DO} loop is entered |
|
(and @code{LOOP} iterates until they become equal by wrap-around |
|
arithmetic). This behaviour is usually not what you want. Therefore, |
|
Gforth offers @code{+DO} and @code{U+DO} (as replacements for |
|
@code{?DO}), which do not enter the loop if @var{start} is greater than |
|
@var{limit}; @code{+DO} is for signed loop parameters, @code{U+DO} for |
|
unsigned loop parameters. |
|
|
@code{LOOP} can be replaced with @code{@var{n} +LOOP}; this updates the |
@code{LOOP} can be replaced with @code{@var{n} +LOOP}; this updates the |
index by @var{n} instead of by 1. The loop is terminated when the border |
index by @var{n} instead of by 1. The loop is terminated when the border |
between @var{limit-1} and @var{limit} is crossed. E.g.: |
between @var{limit-1} and @var{limit} is crossed. E.g.: |
|
|
4 0 ?DO i . 2 +LOOP prints 0 2 |
@code{4 0 +DO i . 2 +LOOP} prints @code{0 2} |
|
|
4 1 ?DO i . 2 +LOOP prints 1 3 |
@code{4 1 +DO i . 2 +LOOP} prints @code{1 3} |
|
|
|
@cindex negative increment for counted loops |
|
@cindex counted loops with negative increment |
The behaviour of @code{@var{n} +LOOP} is peculiar when @var{n} is negative: |
The behaviour of @code{@var{n} +LOOP} is peculiar when @var{n} is negative: |
|
|
-1 0 ?DO i . -1 +LOOP prints 0 -1 |
@code{-1 0 ?DO i . -1 +LOOP} prints @code{0 -1} |
|
|
0 0 ?DO i . -1 +LOOP prints nothing |
@code{ 0 0 ?DO i . -1 +LOOP} prints nothing |
|
|
Therefore we recommend avoiding using @code{@var{n} +LOOP} with negative |
Therefore we recommend avoiding @code{@var{n} +LOOP} with negative |
@var{n}. One alternative is @code{@var{n} S+LOOP}, where the negative |
@var{n}. One alternative is @code{@var{u} -LOOP}, which reduces the |
case behaves symmetrical to the positive case: |
index by @var{u} each iteration. The loop is terminated when the border |
|
between @var{limit+1} and @var{limit} is crossed. Gforth also provides |
|
@code{-DO} and @code{U-DO} for down-counting loops. E.g.: |
|
|
-2 0 ?DO i . -1 +LOOP prints 0 -1 |
@code{-2 0 -DO i . 1 -LOOP} prints @code{0 -1} |
|
|
-1 0 ?DO i . -1 +LOOP prints 0 |
@code{-1 0 -DO i . 1 -LOOP} prints @code{0} |
|
|
0 0 ?DO i . -1 +LOOP prints nothing |
@code{ 0 0 -DO i . 1 -LOOP} prints nothing |
|
|
The loop is terminated when the border between @var{limit-sgn(n)} and |
Unfortunately, @code{+DO}, @code{U+DO}, @code{-DO}, @code{U-DO} and |
@var{limit} is crossed. However, @code{S+LOOP} is not part of the ANS |
@code{-LOOP} are not in the ANS Forth standard. However, an |
Forth standard. |
implementation for these words that uses only standard words is provided |
|
in @file{compat/loops.fs}. |
|
|
@code{?DO} can be replaced by @code{DO}. @code{DO} enters the loop even |
@code{?DO} can also be replaced by @code{DO}. @code{DO} always enters |
when the start and the limit value are equal. We do not recommend using |
the loop, independent of the loop parameters. Do not use @code{DO}, even |
@code{DO}. It will just give you maintenance troubles. |
if you know that the loop is entered in any case. Such knowledge tends |
|
to become invalid during maintenance of a program, and then the |
|
@code{DO} will make trouble. |
|
|
@code{UNLOOP} is used to prepare for an abnormal loop exit, e.g., via |
@code{UNLOOP} is used to prepare for an abnormal loop exit, e.g., via |
@code{EXIT}. @code{UNLOOP} removes the loop control parameters from the |
@code{EXIT}. @code{UNLOOP} removes the loop control parameters from the |
return stack so @code{EXIT} can get to its return address. |
return stack so @code{EXIT} can get to its return address. |
|
|
|
@cindex @code{FOR} loops |
Another counted loop is |
Another counted loop is |
@example |
@example |
@var{n} |
@var{n} |
Line 729 FOR
|
Line 1442 FOR
|
NEXT |
NEXT |
@end example |
@end example |
This is the preferred loop of native code compiler writers who are too |
This is the preferred loop of native code compiler writers who are too |
lazy to optimize @code{?DO} loops properly. In GNU Forth, this loop |
lazy to optimize @code{?DO} loops properly. In Gforth, this loop |
iterates @var{n+1} times; @code{i} produces values starting with @var{n} |
iterates @var{n+1} times; @code{i} produces values starting with @var{n} |
and ending with 0. Other Forth systems may behave differently, even if |
and ending with 0. Other Forth systems may behave differently, even if |
they support @code{FOR} loops. |
they support @code{FOR} loops. To avoid problems, don't use @code{FOR} |
|
loops. |
|
|
@node Locals |
@node Arbitrary control structures, Calls and returns, Counted Loops, Control Structures |
|
@subsection Arbitrary control structures |
|
@cindex control structures, user-defined |
|
|
|
@cindex control-flow stack |
|
ANS Forth permits and supports using control structures in a non-nested |
|
way. Information about incomplete control structures is stored on the |
|
control-flow stack. This stack may be implemented on the Forth data |
|
stack, and this is what we have done in Gforth. |
|
|
|
@cindex @code{orig}, control-flow stack item |
|
@cindex @code{dest}, control-flow stack item |
|
An @i{orig} entry represents an unresolved forward branch, a @i{dest} |
|
entry represents a backward branch target. A few words are the basis for |
|
building any control structure possible (except control structures that |
|
need storage, like calls, coroutines, and backtracking). |
|
|
|
doc-if |
|
doc-ahead |
|
doc-then |
|
doc-begin |
|
doc-until |
|
doc-again |
|
doc-cs-pick |
|
doc-cs-roll |
|
|
|
On many systems control-flow stack items take one word, in Gforth they |
|
currently take three (this may change in the future). Therefore it is a |
|
really good idea to manipulate the control flow stack with |
|
@code{cs-pick} and @code{cs-roll}, not with data stack manipulation |
|
words. |
|
|
|
Some standard control structure words are built from these words: |
|
|
|
doc-else |
|
doc-while |
|
doc-repeat |
|
|
|
Gforth adds some more control-structure words: |
|
|
|
doc-endif |
|
doc-?dup-if |
|
doc-?dup-0=-if |
|
|
|
Counted loop words constitute a separate group of words: |
|
|
|
doc-?do |
|
doc-+do |
|
doc-u+do |
|
doc--do |
|
doc-u-do |
|
doc-do |
|
doc-for |
|
doc-loop |
|
doc-+loop |
|
doc--loop |
|
doc-next |
|
doc-leave |
|
doc-?leave |
|
doc-unloop |
|
doc-done |
|
|
|
The standard does not allow using @code{cs-pick} and @code{cs-roll} on |
|
@i{do-sys}. Our system allows it, but it's your job to ensure that for |
|
every @code{?DO} etc. there is exactly one @code{UNLOOP} on any path |
|
through the definition (@code{LOOP} etc. compile an @code{UNLOOP} on the |
|
fall-through path). Also, you have to ensure that all @code{LEAVE}s are |
|
resolved (by using one of the loop-ending words or @code{DONE}). |
|
|
|
Another group of control structure words are |
|
|
|
doc-case |
|
doc-endcase |
|
doc-of |
|
doc-endof |
|
|
|
@i{case-sys} and @i{of-sys} cannot be processed using @code{cs-pick} and |
|
@code{cs-roll}. |
|
|
|
@subsubsection Programming Style |
|
|
|
In order to ensure readability we recommend that you do not create |
|
arbitrary control structures directly, but define new control structure |
|
words for the control structure you want and use these words in your |
|
program. |
|
|
|
E.g., instead of writing |
|
|
|
@example |
|
begin |
|
... |
|
if [ 1 cs-roll ] |
|
... |
|
again then |
|
@end example |
|
|
|
we recommend defining control structure words, e.g., |
|
|
|
@example |
|
: while ( dest -- orig dest ) |
|
POSTPONE if |
|
1 cs-roll ; immediate |
|
|
|
: repeat ( orig dest -- ) |
|
POSTPONE again |
|
POSTPONE then ; immediate |
|
@end example |
|
|
|
and then using these to create the control structure: |
|
|
|
@example |
|
begin |
|
... |
|
while |
|
... |
|
repeat |
|
@end example |
|
|
|
That's much easier to read, isn't it? Of course, @code{REPEAT} and |
|
@code{WHILE} are predefined, so in this example it would not be |
|
necessary to define them. |
|
|
|
@node Calls and returns, Exception Handling, Arbitrary control structures, Control Structures |
|
@subsection Calls and returns |
|
@cindex calling a definition |
|
@cindex returning from a definition |
|
|
|
A definition can be called simply be writing the name of the |
|
definition. When the end of the definition is reached, it returns. An |
|
earlier return can be forced using |
|
|
|
doc-exit |
|
|
|
Don't forget to clean up the return stack and @code{UNLOOP} any |
|
outstanding @code{?DO}...@code{LOOP}s before @code{EXIT}ing. The |
|
primitive compiled by @code{EXIT} is |
|
|
|
doc-;s |
|
|
|
@node Exception Handling, , Calls and returns, Control Structures |
|
@subsection Exception Handling |
|
@cindex Exceptions |
|
|
|
doc-catch |
|
doc-throw |
|
|
|
@node Locals, Defining Words, Control Structures, Words |
@section Locals |
@section Locals |
|
@cindex locals |
|
|
|
Local variables can make Forth programming more enjoyable and Forth |
|
programs easier to read. Unfortunately, the locals of ANS Forth are |
|
laden with restrictions. Therefore, we provide not only the ANS Forth |
|
locals wordset, but also our own, more powerful locals wordset (we |
|
implemented the ANS Forth locals wordset through our locals wordset). |
|
|
|
The ideas in this section have also been published in the paper |
|
@cite{Automatic Scoping of Local Variables} by M. Anton Ertl, presented |
|
at EuroForth '94; it is available at |
|
@*@file{http://www.complang.tuwien.ac.at/papers/ertl94l.ps.gz}. |
|
|
|
@menu |
|
* Gforth locals:: |
|
* ANS Forth locals:: |
|
@end menu |
|
|
|
@node Gforth locals, ANS Forth locals, Locals, Locals |
|
@subsection Gforth locals |
|
@cindex Gforth locals |
|
@cindex locals, Gforth style |
|
|
|
Locals can be defined with |
|
|
|
@example |
|
@{ local1 local2 ... -- comment @} |
|
@end example |
|
or |
|
@example |
|
@{ local1 local2 ... @} |
|
@end example |
|
|
|
E.g., |
|
@example |
|
: max @{ n1 n2 -- n3 @} |
|
n1 n2 > if |
|
n1 |
|
else |
|
n2 |
|
endif ; |
|
@end example |
|
|
|
The similarity of locals definitions with stack comments is intended. A |
|
locals definition often replaces the stack comment of a word. The order |
|
of the locals corresponds to the order in a stack comment and everything |
|
after the @code{--} is really a comment. |
|
|
|
This similarity has one disadvantage: It is too easy to confuse locals |
|
declarations with stack comments, causing bugs and making them hard to |
|
find. However, this problem can be avoided by appropriate coding |
|
conventions: Do not use both notations in the same program. If you do, |
|
they should be distinguished using additional means, e.g. by position. |
|
|
|
@cindex types of locals |
|
@cindex locals types |
|
The name of the local may be preceded by a type specifier, e.g., |
|
@code{F:} for a floating point value: |
|
|
|
@example |
|
: CX* @{ F: Ar F: Ai F: Br F: Bi -- Cr Ci @} |
|
\ complex multiplication |
|
Ar Br f* Ai Bi f* f- |
|
Ar Bi f* Ai Br f* f+ ; |
|
@end example |
|
|
|
@cindex flavours of locals |
|
@cindex locals flavours |
|
@cindex value-flavoured locals |
|
@cindex variable-flavoured locals |
|
Gforth currently supports cells (@code{W:}, @code{W^}), doubles |
|
(@code{D:}, @code{D^}), floats (@code{F:}, @code{F^}) and characters |
|
(@code{C:}, @code{C^}) in two flavours: a value-flavoured local (defined |
|
with @code{W:}, @code{D:} etc.) produces its value and can be changed |
|
with @code{TO}. A variable-flavoured local (defined with @code{W^} etc.) |
|
produces its address (which becomes invalid when the variable's scope is |
|
left). E.g., the standard word @code{emit} can be defined in terms of |
|
@code{type} like this: |
|
|
|
@example |
|
: emit @{ C^ char* -- @} |
|
char* 1 type ; |
|
@end example |
|
|
|
@cindex default type of locals |
|
@cindex locals, default type |
|
A local without type specifier is a @code{W:} local. Both flavours of |
|
locals are initialized with values from the data or FP stack. |
|
|
|
Currently there is no way to define locals with user-defined data |
|
structures, but we are working on it. |
|
|
|
Gforth allows defining locals everywhere in a colon definition. This |
|
poses the following questions: |
|
|
|
@menu |
|
* Where are locals visible by name?:: |
|
* How long do locals live?:: |
|
* Programming Style:: |
|
* Implementation:: |
|
@end menu |
|
|
|
@node Where are locals visible by name?, How long do locals live?, Gforth locals, Gforth locals |
|
@subsubsection Where are locals visible by name? |
|
@cindex locals visibility |
|
@cindex visibility of locals |
|
@cindex scope of locals |
|
|
|
Basically, the answer is that locals are visible where you would expect |
|
it in block-structured languages, and sometimes a little longer. If you |
|
want to restrict the scope of a local, enclose its definition in |
|
@code{SCOPE}...@code{ENDSCOPE}. |
|
|
|
doc-scope |
|
doc-endscope |
|
|
|
These words behave like control structure words, so you can use them |
|
with @code{CS-PICK} and @code{CS-ROLL} to restrict the scope in |
|
arbitrary ways. |
|
|
|
If you want a more exact answer to the visibility question, here's the |
|
basic principle: A local is visible in all places that can only be |
|
reached through the definition of the local@footnote{In compiler |
|
construction terminology, all places dominated by the definition of the |
|
local.}. In other words, it is not visible in places that can be reached |
|
without going through the definition of the local. E.g., locals defined |
|
in @code{IF}...@code{ENDIF} are visible until the @code{ENDIF}, locals |
|
defined in @code{BEGIN}...@code{UNTIL} are visible after the |
|
@code{UNTIL} (until, e.g., a subsequent @code{ENDSCOPE}). |
|
|
|
The reasoning behind this solution is: We want to have the locals |
|
visible as long as it is meaningful. The user can always make the |
|
visibility shorter by using explicit scoping. In a place that can |
|
only be reached through the definition of a local, the meaning of a |
|
local name is clear. In other places it is not: How is the local |
|
initialized at the control flow path that does not contain the |
|
definition? Which local is meant, if the same name is defined twice in |
|
two independent control flow paths? |
|
|
|
This should be enough detail for nearly all users, so you can skip the |
|
rest of this section. If you really must know all the gory details and |
|
options, read on. |
|
|
|
In order to implement this rule, the compiler has to know which places |
|
are unreachable. It knows this automatically after @code{AHEAD}, |
|
@code{AGAIN}, @code{EXIT} and @code{LEAVE}; in other cases (e.g., after |
|
most @code{THROW}s), you can use the word @code{UNREACHABLE} to tell the |
|
compiler that the control flow never reaches that place. If |
|
@code{UNREACHABLE} is not used where it could, the only consequence is |
|
that the visibility of some locals is more limited than the rule above |
|
says. If @code{UNREACHABLE} is used where it should not (i.e., if you |
|
lie to the compiler), buggy code will be produced. |
|
|
|
doc-unreachable |
|
|
|
Another problem with this rule is that at @code{BEGIN}, the compiler |
|
does not know which locals will be visible on the incoming |
|
back-edge. All problems discussed in the following are due to this |
|
ignorance of the compiler (we discuss the problems using @code{BEGIN} |
|
loops as examples; the discussion also applies to @code{?DO} and other |
|
loops). Perhaps the most insidious example is: |
|
@example |
|
AHEAD |
|
BEGIN |
|
x |
|
[ 1 CS-ROLL ] THEN |
|
@{ x @} |
|
... |
|
UNTIL |
|
@end example |
|
|
|
This should be legal according to the visibility rule. The use of |
|
@code{x} can only be reached through the definition; but that appears |
|
textually below the use. |
|
|
|
From this example it is clear that the visibility rules cannot be fully |
|
implemented without major headaches. Our implementation treats common |
|
cases as advertised and the exceptions are treated in a safe way: The |
|
compiler makes a reasonable guess about the locals visible after a |
|
@code{BEGIN}; if it is too pessimistic, the |
|
user will get a spurious error about the local not being defined; if the |
|
compiler is too optimistic, it will notice this later and issue a |
|
warning. In the case above the compiler would complain about @code{x} |
|
being undefined at its use. You can see from the obscure examples in |
|
this section that it takes quite unusual control structures to get the |
|
compiler into trouble, and even then it will often do fine. |
|
|
|
If the @code{BEGIN} is reachable from above, the most optimistic guess |
|
is that all locals visible before the @code{BEGIN} will also be |
|
visible after the @code{BEGIN}. This guess is valid for all loops that |
|
are entered only through the @code{BEGIN}, in particular, for normal |
|
@code{BEGIN}...@code{WHILE}...@code{REPEAT} and |
|
@code{BEGIN}...@code{UNTIL} loops and it is implemented in our |
|
compiler. When the branch to the @code{BEGIN} is finally generated by |
|
@code{AGAIN} or @code{UNTIL}, the compiler checks the guess and |
|
warns the user if it was too optimistic: |
|
@example |
|
IF |
|
@{ x @} |
|
BEGIN |
|
\ x ? |
|
[ 1 cs-roll ] THEN |
|
... |
|
UNTIL |
|
@end example |
|
|
|
Here, @code{x} lives only until the @code{BEGIN}, but the compiler |
|
optimistically assumes that it lives until the @code{THEN}. It notices |
|
this difference when it compiles the @code{UNTIL} and issues a |
|
warning. The user can avoid the warning, and make sure that @code{x} |
|
is not used in the wrong area by using explicit scoping: |
|
@example |
|
IF |
|
SCOPE |
|
@{ x @} |
|
ENDSCOPE |
|
BEGIN |
|
[ 1 cs-roll ] THEN |
|
... |
|
UNTIL |
|
@end example |
|
|
|
Since the guess is optimistic, there will be no spurious error messages |
|
about undefined locals. |
|
|
|
If the @code{BEGIN} is not reachable from above (e.g., after |
|
@code{AHEAD} or @code{EXIT}), the compiler cannot even make an |
|
optimistic guess, as the locals visible after the @code{BEGIN} may be |
|
defined later. Therefore, the compiler assumes that no locals are |
|
visible after the @code{BEGIN}. However, the user can use |
|
@code{ASSUME-LIVE} to make the compiler assume that the same locals are |
|
visible at the BEGIN as at the point where the top control-flow stack |
|
item was created. |
|
|
|
doc-assume-live |
|
|
|
E.g., |
|
@example |
|
@{ x @} |
|
AHEAD |
|
ASSUME-LIVE |
|
BEGIN |
|
x |
|
[ 1 CS-ROLL ] THEN |
|
... |
|
UNTIL |
|
@end example |
|
|
|
Other cases where the locals are defined before the @code{BEGIN} can be |
|
handled by inserting an appropriate @code{CS-ROLL} before the |
|
@code{ASSUME-LIVE} (and changing the control-flow stack manipulation |
|
behind the @code{ASSUME-LIVE}). |
|
|
|
Cases where locals are defined after the @code{BEGIN} (but should be |
|
visible immediately after the @code{BEGIN}) can only be handled by |
|
rearranging the loop. E.g., the ``most insidious'' example above can be |
|
arranged into: |
|
@example |
|
BEGIN |
|
@{ x @} |
|
... 0= |
|
WHILE |
|
x |
|
REPEAT |
|
@end example |
|
|
|
@node How long do locals live?, Programming Style, Where are locals visible by name?, Gforth locals |
|
@subsubsection How long do locals live? |
|
@cindex locals lifetime |
|
@cindex lifetime of locals |
|
|
|
The right answer for the lifetime question would be: A local lives at |
|
least as long as it can be accessed. For a value-flavoured local this |
|
means: until the end of its visibility. However, a variable-flavoured |
|
local could be accessed through its address far beyond its visibility |
|
scope. Ultimately, this would mean that such locals would have to be |
|
garbage collected. Since this entails un-Forth-like implementation |
|
complexities, I adopted the same cowardly solution as some other |
|
languages (e.g., C): The local lives only as long as it is visible; |
|
afterwards its address is invalid (and programs that access it |
|
afterwards are erroneous). |
|
|
|
@node Programming Style, Implementation, How long do locals live?, Gforth locals |
|
@subsubsection Programming Style |
|
@cindex locals programming style |
|
@cindex programming style, locals |
|
|
|
The freedom to define locals anywhere has the potential to change |
|
programming styles dramatically. In particular, the need to use the |
|
return stack for intermediate storage vanishes. Moreover, all stack |
|
manipulations (except @code{PICK}s and @code{ROLL}s with run-time |
|
determined arguments) can be eliminated: If the stack items are in the |
|
wrong order, just write a locals definition for all of them; then |
|
write the items in the order you want. |
|
|
|
This seems a little far-fetched and eliminating stack manipulations is |
|
unlikely to become a conscious programming objective. Still, the number |
|
of stack manipulations will be reduced dramatically if local variables |
|
are used liberally (e.g., compare @code{max} in @ref{Gforth locals} with |
|
a traditional implementation of @code{max}). |
|
|
|
This shows one potential benefit of locals: making Forth programs more |
|
readable. Of course, this benefit will only be realized if the |
|
programmers continue to honour the principle of factoring instead of |
|
using the added latitude to make the words longer. |
|
|
|
@cindex single-assignment style for locals |
|
Using @code{TO} can and should be avoided. Without @code{TO}, |
|
every value-flavoured local has only a single assignment and many |
|
advantages of functional languages apply to Forth. I.e., programs are |
|
easier to analyse, to optimize and to read: It is clear from the |
|
definition what the local stands for, it does not turn into something |
|
different later. |
|
|
|
E.g., a definition using @code{TO} might look like this: |
|
@example |
|
: strcmp @{ addr1 u1 addr2 u2 -- n @} |
|
u1 u2 min 0 |
|
?do |
|
addr1 c@@ addr2 c@@ - |
|
?dup-if |
|
unloop exit |
|
then |
|
addr1 char+ TO addr1 |
|
addr2 char+ TO addr2 |
|
loop |
|
u1 u2 - ; |
|
@end example |
|
Here, @code{TO} is used to update @code{addr1} and @code{addr2} at |
|
every loop iteration. @code{strcmp} is a typical example of the |
|
readability problems of using @code{TO}. When you start reading |
|
@code{strcmp}, you think that @code{addr1} refers to the start of the |
|
string. Only near the end of the loop you realize that it is something |
|
else. |
|
|
|
This can be avoided by defining two locals at the start of the loop that |
|
are initialized with the right value for the current iteration. |
|
@example |
|
: strcmp @{ addr1 u1 addr2 u2 -- n @} |
|
addr1 addr2 |
|
u1 u2 min 0 |
|
?do @{ s1 s2 @} |
|
s1 c@@ s2 c@@ - |
|
?dup-if |
|
unloop exit |
|
then |
|
s1 char+ s2 char+ |
|
loop |
|
2drop |
|
u1 u2 - ; |
|
@end example |
|
Here it is clear from the start that @code{s1} has a different value |
|
in every loop iteration. |
|
|
|
@node Implementation, , Programming Style, Gforth locals |
|
@subsubsection Implementation |
|
@cindex locals implementation |
|
@cindex implementation of locals |
|
|
|
@cindex locals stack |
|
Gforth uses an extra locals stack. The most compelling reason for |
|
this is that the return stack is not float-aligned; using an extra stack |
|
also eliminates the problems and restrictions of using the return stack |
|
as locals stack. Like the other stacks, the locals stack grows toward |
|
lower addresses. A few primitives allow an efficient implementation: |
|
|
|
doc-@local# |
|
doc-f@local# |
|
doc-laddr# |
|
doc-lp+!# |
|
doc-lp! |
|
doc->l |
|
doc-f>l |
|
|
|
In addition to these primitives, some specializations of these |
|
primitives for commonly occurring inline arguments are provided for |
|
efficiency reasons, e.g., @code{@@local0} as specialization of |
|
@code{@@local#} for the inline argument 0. The following compiling words |
|
compile the right specialized version, or the general version, as |
|
appropriate: |
|
|
|
doc-compile-@local |
|
doc-compile-f@local |
|
doc-compile-lp+! |
|
|
|
Combinations of conditional branches and @code{lp+!#} like |
|
@code{?branch-lp+!#} (the locals pointer is only changed if the branch |
|
is taken) are provided for efficiency and correctness in loops. |
|
|
|
A special area in the dictionary space is reserved for keeping the |
|
local variable names. @code{@{} switches the dictionary pointer to this |
|
area and @code{@}} switches it back and generates the locals |
|
initializing code. @code{W:} etc.@ are normal defining words. This |
|
special area is cleared at the start of every colon definition. |
|
|
|
@cindex wordlist for defining locals |
|
A special feature of Gforth's dictionary is used to implement the |
|
definition of locals without type specifiers: every wordlist (aka |
|
vocabulary) has its own methods for searching |
|
etc. (@pxref{Wordlists}). For the present purpose we defined a wordlist |
|
with a special search method: When it is searched for a word, it |
|
actually creates that word using @code{W:}. @code{@{} changes the search |
|
order to first search the wordlist containing @code{@}}, @code{W:} etc., |
|
and then the wordlist for defining locals without type specifiers. |
|
|
|
The lifetime rules support a stack discipline within a colon |
|
definition: The lifetime of a local is either nested with other locals |
|
lifetimes or it does not overlap them. |
|
|
|
At @code{BEGIN}, @code{IF}, and @code{AHEAD} no code for locals stack |
|
pointer manipulation is generated. Between control structure words |
|
locals definitions can push locals onto the locals stack. @code{AGAIN} |
|
is the simplest of the other three control flow words. It has to |
|
restore the locals stack depth of the corresponding @code{BEGIN} |
|
before branching. The code looks like this: |
|
@format |
|
@code{lp+!#} current-locals-size @minus{} dest-locals-size |
|
@code{branch} <begin> |
|
@end format |
|
|
|
@code{UNTIL} is a little more complicated: If it branches back, it |
|
must adjust the stack just like @code{AGAIN}. But if it falls through, |
|
the locals stack must not be changed. The compiler generates the |
|
following code: |
|
@format |
|
@code{?branch-lp+!#} <begin> current-locals-size @minus{} dest-locals-size |
|
@end format |
|
The locals stack pointer is only adjusted if the branch is taken. |
|
|
|
@code{THEN} can produce somewhat inefficient code: |
|
@format |
|
@code{lp+!#} current-locals-size @minus{} orig-locals-size |
|
<orig target>: |
|
@code{lp+!#} orig-locals-size @minus{} new-locals-size |
|
@end format |
|
The second @code{lp+!#} adjusts the locals stack pointer from the |
|
level at the @var{orig} point to the level after the @code{THEN}. The |
|
first @code{lp+!#} adjusts the locals stack pointer from the current |
|
level to the level at the orig point, so the complete effect is an |
|
adjustment from the current level to the right level after the |
|
@code{THEN}. |
|
|
|
@cindex locals information on the control-flow stack |
|
@cindex control-flow stack items, locals information |
|
In a conventional Forth implementation a dest control-flow stack entry |
|
is just the target address and an orig entry is just the address to be |
|
patched. Our locals implementation adds a wordlist to every orig or dest |
|
item. It is the list of locals visible (or assumed visible) at the point |
|
described by the entry. Our implementation also adds a tag to identify |
|
the kind of entry, in particular to differentiate between live and dead |
|
(reachable and unreachable) orig entries. |
|
|
|
A few unusual operations have to be performed on locals wordlists: |
|
|
|
doc-common-list |
|
doc-sub-list? |
|
doc-list-size |
|
|
|
Several features of our locals wordlist implementation make these |
|
operations easy to implement: The locals wordlists are organised as |
|
linked lists; the tails of these lists are shared, if the lists |
|
contain some of the same locals; and the address of a name is greater |
|
than the address of the names behind it in the list. |
|
|
|
Another important implementation detail is the variable |
|
@code{dead-code}. It is used by @code{BEGIN} and @code{THEN} to |
|
determine if they can be reached directly or only through the branch |
|
that they resolve. @code{dead-code} is set by @code{UNREACHABLE}, |
|
@code{AHEAD}, @code{EXIT} etc., and cleared at the start of a colon |
|
definition, by @code{BEGIN} and usually by @code{THEN}. |
|
|
|
Counted loops are similar to other loops in most respects, but |
|
@code{LEAVE} requires special attention: It performs basically the same |
|
service as @code{AHEAD}, but it does not create a control-flow stack |
|
entry. Therefore the information has to be stored elsewhere; |
|
traditionally, the information was stored in the target fields of the |
|
branches created by the @code{LEAVE}s, by organizing these fields into a |
|
linked list. Unfortunately, this clever trick does not provide enough |
|
space for storing our extended control flow information. Therefore, we |
|
introduce another stack, the leave stack. It contains the control-flow |
|
stack entries for all unresolved @code{LEAVE}s. |
|
|
|
Local names are kept until the end of the colon definition, even if |
|
they are no longer visible in any control-flow path. In a few cases |
|
this may lead to increased space needs for the locals name area, but |
|
usually less than reclaiming this space would cost in code size. |
|
|
|
|
|
@node ANS Forth locals, , Gforth locals, Locals |
|
@subsection ANS Forth locals |
|
@cindex locals, ANS Forth style |
|
|
|
The ANS Forth locals wordset does not define a syntax for locals, but |
|
words that make it possible to define various syntaxes. One of the |
|
possible syntaxes is a subset of the syntax we used in the Gforth locals |
|
wordset, i.e.: |
|
|
|
@example |
|
@{ local1 local2 ... -- comment @} |
|
@end example |
|
or |
|
@example |
|
@{ local1 local2 ... @} |
|
@end example |
|
|
|
The order of the locals corresponds to the order in a stack comment. The |
|
restrictions are: |
|
|
|
@itemize @bullet |
|
@item |
|
Locals can only be cell-sized values (no type specifiers are allowed). |
|
@item |
|
Locals can be defined only outside control structures. |
|
@item |
|
Locals can interfere with explicit usage of the return stack. For the |
|
exact (and long) rules, see the standard. If you don't use return stack |
|
accessing words in a definition using locals, you will be all right. The |
|
purpose of this rule is to make locals implementation on the return |
|
stack easier. |
|
@item |
|
The whole definition must be in one line. |
|
@end itemize |
|
|
|
Locals defined in this way behave like @code{VALUE}s (@xref{Simple |
|
Defining Words}). I.e., they are initialized from the stack. Using their |
|
name produces their value. Their value can be changed using @code{TO}. |
|
|
|
Since this syntax is supported by Gforth directly, you need not do |
|
anything to use it. If you want to port a program using this syntax to |
|
another ANS Forth system, use @file{compat/anslocal.fs} to implement the |
|
syntax on the other system. |
|
|
|
Note that a syntax shown in the standard, section A.13 looks |
|
similar, but is quite different in having the order of locals |
|
reversed. Beware! |
|
|
|
The ANS Forth locals wordset itself consists of the following word |
|
|
|
doc-(local) |
|
|
|
The ANS Forth locals extension wordset defines a syntax, but it is so |
|
awful that we strongly recommend not to use it. We have implemented this |
|
syntax to make porting to Gforth easy, but do not document it here. The |
|
problem with this syntax is that the locals are defined in an order |
|
reversed with respect to the standard stack comment notation, making |
|
programs harder to read, and easier to misread and miswrite. The only |
|
merit of this syntax is that it is easy to implement using the ANS Forth |
|
locals wordset. |
|
|
|
@node Defining Words, Tokens for Words, Locals, Words |
|
@section Defining Words |
|
@cindex defining words |
|
|
|
@menu |
|
* Simple Defining Words:: |
|
* Colon Definitions:: |
|
* User-defined Defining Words:: |
|
* Supplying names:: |
|
* Interpretation and Compilation Semantics:: |
|
@end menu |
|
|
|
@node Simple Defining Words, Colon Definitions, Defining Words, Defining Words |
|
@subsection Simple Defining Words |
|
@cindex simple defining words |
|
@cindex defining words, simple |
|
|
|
doc-constant |
|
doc-2constant |
|
doc-fconstant |
|
doc-variable |
|
doc-2variable |
|
doc-fvariable |
|
doc-create |
|
doc-user |
|
doc-value |
|
doc-to |
|
doc-defer |
|
doc-is |
|
|
|
@node Colon Definitions, User-defined Defining Words, Simple Defining Words, Defining Words |
|
@subsection Colon Definitions |
|
@cindex colon definitions |
|
|
|
@example |
|
: name ( ... -- ... ) |
|
word1 word2 word3 ; |
|
@end example |
|
|
|
creates a word called @code{name}, that, upon execution, executes |
|
@code{word1 word2 word3}. @code{name} is a @dfn{(colon) definition}. |
|
|
|
The explanation above is somewhat superficial. @xref{Interpretation and |
|
Compilation Semantics} for an in-depth discussion of some of the issues |
|
involved. |
|
|
|
doc-: |
|
doc-; |
|
|
|
@node User-defined Defining Words, Supplying names, Colon Definitions, Defining Words |
|
@subsection User-defined Defining Words |
|
@cindex user-defined defining words |
|
@cindex defining words, user-defined |
|
|
|
You can create new defining words simply by wrapping defining-time code |
|
around existing defining words and putting the sequence in a colon |
|
definition. |
|
|
|
@cindex @code{CREATE} ... @code{DOES>} |
|
If you want the words defined with your defining words to behave |
|
differently from words defined with standard defining words, you can |
|
write your defining word like this: |
|
|
|
@example |
|
: def-word ( "name" -- ) |
|
Create @var{code1} |
|
DOES> ( ... -- ... ) |
|
@var{code2} ; |
|
|
|
def-word name |
|
@end example |
|
|
|
Technically, this fragment defines a defining word @code{def-word}, and |
|
a word @code{name}; when you execute @code{name}, the address of the |
|
body of @code{name} is put on the data stack and @var{code2} is executed |
|
(the address of the body of @code{name} is the address @code{HERE} |
|
returns immediately after the @code{CREATE}). |
|
|
|
In other words, if you make the following definitions: |
|
|
|
@example |
|
: def-word1 ( "name" -- ) |
|
Create @var{code1} ; |
|
|
|
: action1 ( ... -- ... ) |
|
@var{code2} ; |
|
|
|
def-word name1 |
|
@end example |
|
|
|
Using @code{name1 action1} is equivalent to using @code{name}. |
|
|
|
E.g., you can implement @code{Constant} in this way: |
|
|
|
@example |
|
: constant ( w "name" -- ) |
|
create , |
|
DOES> ( -- w ) |
|
@@ ; |
|
@end example |
|
|
|
When you create a constant with @code{5 constant five}, first a new word |
|
@code{five} is created, then the value 5 is laid down in the body of |
|
@code{five} with @code{,}. When @code{five} is invoked, the address of |
|
the body is put on the stack, and @code{@@} retrieves the value 5. |
|
|
|
@cindex stack effect of @code{DOES>}-parts |
|
@cindex @code{DOES>}-parts, stack effect |
|
In the example above the stack comment after the @code{DOES>} specifies |
|
the stack effect of the defined words, not the stack effect of the |
|
following code (the following code expects the address of the body on |
|
the top of stack, which is not reflected in the stack comment). This is |
|
the convention that I use and recommend (it clashes a bit with using |
|
locals declarations for stack effect specification, though). |
|
|
|
@subsubsection Applications of @code{CREATE..DOES>} |
|
@cindex @code{CREATE} ... @code{DOES>}, applications |
|
|
|
You may wonder how to use this feature. Here are some usage patterns: |
|
|
|
@cindex factoring similar colon definitions |
|
When you see a sequence of code occurring several times, and you can |
|
identify a meaning, you will factor it out as a colon definition. When |
|
you see similar colon definitions, you can factor them using |
|
@code{CREATE..DOES>}. E.g., an assembler usually defines several words |
|
that look very similar: |
|
@example |
|
: ori, ( reg-target reg-source n -- ) |
|
0 asm-reg-reg-imm ; |
|
: andi, ( reg-target reg-source n -- ) |
|
1 asm-reg-reg-imm ; |
|
@end example |
|
|
|
This could be factored with: |
|
@example |
|
: reg-reg-imm ( op-code -- ) |
|
create , |
|
DOES> ( reg-target reg-source n -- ) |
|
@@ asm-reg-reg-imm ; |
|
|
|
0 reg-reg-imm ori, |
|
1 reg-reg-imm andi, |
|
@end example |
|
|
|
@cindex currying |
|
Another view of @code{CREATE..DOES>} is to consider it as a crude way to |
|
supply a part of the parameters for a word (known as @dfn{currying} in |
|
the functional language community). E.g., @code{+} needs two |
|
parameters. Creating versions of @code{+} with one parameter fixed can |
|
be done like this: |
|
@example |
|
: curry+ ( n1 -- ) |
|
create , |
|
DOES> ( n2 -- n1+n2 ) |
|
@@ + ; |
|
|
|
3 curry+ 3+ |
|
-2 curry+ 2- |
|
@end example |
|
|
|
@subsubsection The gory details of @code{CREATE..DOES>} |
|
@cindex @code{CREATE} ... @code{DOES>}, details |
|
|
|
doc-does> |
|
|
|
@cindex @code{DOES>} in a separate definition |
|
This means that you need not use @code{CREATE} and @code{DOES>} in the |
|
same definition; E.g., you can put the @code{DOES>}-part in a separate |
|
definition. This allows us to, e.g., select among different DOES>-parts: |
|
@example |
|
: does1 |
|
DOES> ( ... -- ... ) |
|
... ; |
|
|
|
: does2 |
|
DOES> ( ... -- ... ) |
|
... ; |
|
|
|
: def-word ( ... -- ... ) |
|
create ... |
|
IF |
|
does1 |
|
ELSE |
|
does2 |
|
ENDIF ; |
|
@end example |
|
|
|
@cindex @code{DOES>} in interpretation state |
|
In a standard program you can apply a @code{DOES>}-part only if the last |
|
word was defined with @code{CREATE}. In Gforth, the @code{DOES>}-part |
|
will override the behaviour of the last word defined in any case. In a |
|
standard program, you can use @code{DOES>} only in a colon |
|
definition. In Gforth, you can also use it in interpretation state, in a |
|
kind of one-shot mode: |
|
@example |
|
CREATE name ( ... -- ... ) |
|
@var{initialization} |
|
DOES> |
|
@var{code} ; |
|
@end example |
|
This is equivalent to the standard |
|
@example |
|
:noname |
|
DOES> |
|
@var{code} ; |
|
CREATE name EXECUTE ( ... -- ... ) |
|
@var{initialization} |
|
@end example |
|
|
|
You can get the address of the body of a word with |
|
|
|
doc->body |
|
|
|
@node Supplying names, Interpretation and Compilation Semantics, User-defined Defining Words, Defining Words |
|
@subsection Supplying names for the defined words |
|
@cindex names for defined words |
|
@cindex defining words, name parameter |
|
|
|
@cindex defining words, name given in a string |
|
By default, defining words take the names for the defined words from the |
|
input stream. Sometimes you want to supply the name from a string. You |
|
can do this with |
|
|
|
doc-nextname |
|
|
|
E.g., |
|
|
|
@example |
|
s" foo" nextname create |
|
@end example |
|
is equivalent to |
|
@example |
|
create foo |
|
@end example |
|
|
|
@cindex defining words without name |
|
Sometimes you want to define a word without a name. You can do this with |
|
|
|
doc-noname |
|
|
|
@cindex execution token of last defined word |
|
To make any use of the newly defined word, you need its execution |
|
token. You can get it with |
|
|
|
doc-lastxt |
|
|
|
E.g., you can initialize a deferred word with an anonymous colon |
|
definition: |
|
@example |
|
Defer deferred |
|
noname : ( ... -- ... ) |
|
... ; |
|
lastxt IS deferred |
|
@end example |
|
|
|
@code{lastxt} also works when the last word was not defined as |
|
@code{noname}. |
|
|
|
The standard has also recognized the need for anonymous words and |
|
provides |
|
|
|
doc-:noname |
|
|
|
This leaves the execution token for the word on the stack after the |
|
closing @code{;}. You can rewrite the last example with @code{:noname}: |
|
@example |
|
Defer deferred |
|
:noname ( ... -- ... ) |
|
... ; |
|
IS deferred |
|
@end example |
|
|
|
@node Interpretation and Compilation Semantics, , Supplying names, Defining Words |
|
@subsection Interpretation and Compilation Semantics |
|
@cindex semantics, interpretation and compilation |
|
|
|
@cindex interpretation semantics |
|
The @dfn{interpretation semantics} of a word are what the text |
|
interpreter does when it encounters the word in interpret state. It also |
|
appears in some other contexts, e.g., the execution token returned by |
|
@code{' @var{word}} identifies the interpretation semantics of |
|
@var{word} (in other words, @code{' @var{word} execute} is equivalent to |
|
interpret-state text interpretation of @code{@var{word}}). |
|
|
|
@cindex compilation semantics |
|
The @dfn{compilation semantics} of a word are what the text interpreter |
|
does when it encounters the word in compile state. It also appears in |
|
other contexts, e.g, @code{POSTPONE @var{word}} compiles@footnote{In |
|
standard terminology, ``appends to the current definition''.} the |
|
compilation semantics of @var{word}. |
|
|
|
@cindex execution semantics |
|
The standard also talks about @dfn{execution semantics}. They are used |
|
only for defining the interpretation and compilation semantics of many |
|
words. By default, the interpretation semantics of a word are to |
|
@code{execute} its execution semantics, and the compilation semantics of |
|
a word are to @code{compile,} its execution semantics.@footnote{In |
|
standard terminology: The default interpretation semantics are its |
|
execution semantics; the default compilation semantics are to append its |
|
execution semantics to the execution semantics of the current |
|
definition.} |
|
|
|
@cindex immediate words |
|
You can change the compilation semantics into @code{execute}ing the |
|
execution semantics with |
|
|
|
doc-immediate |
|
|
|
@cindex compile-only words |
|
You can remove the interpretation semantics of a word with |
|
|
|
doc-compile-only |
|
doc-restrict |
|
|
|
Note that ticking (@code{'}) compile-only words gives an error |
|
(``Interpreting a compile-only word''). |
|
|
|
Gforth also allows you to define words with arbitrary combinations of |
|
interpretation and compilation semantics. |
|
|
|
doc-interpret/compile: |
|
|
|
This feature was introduced for implementing @code{TO} and @code{S"}. I |
|
recommend that you do not define such words, as cute as they may be: |
|
they make it hard to get at both parts of the word in some contexts. |
|
E.g., assume you want to get an execution token for the compilation |
|
part. Instead, define two words, one that embodies the interpretation |
|
part, and one that embodies the compilation part. |
|
|
|
There is, however, a potentially useful application of this feature: |
|
Providing differing implementations for the default semantics. While |
|
this introduces redundancy and is therefore usually a bad idea, a |
|
performance improvement may be worth the trouble. E.g., consider the |
|
word @code{foobar}: |
|
|
|
@example |
|
: foobar |
|
foo bar ; |
|
@end example |
|
|
|
Let us assume that @code{foobar} is called so frequently that the |
|
calling overhead would take a significant amount of the run-time. We can |
|
optimize it with @code{interpret/compile:}: |
|
|
|
@example |
|
:noname |
|
foo bar ; |
|
:noname |
|
POSTPONE foo POSTPONE bar ; |
|
interpret/compile: foobar |
|
@end example |
|
|
|
This definition has the same interpretation semantics and essentially |
|
the same compilation semantics as the simple definition of |
|
@code{foobar}, but the implementation of the compilation semantics is |
|
more efficient with respect to run-time. |
|
|
|
@cindex state-smart words are a bad idea |
|
Some people try to use state-smart words to emulate the feature provided |
|
by @code{interpret/compile:} (words are state-smart if they check |
|
@code{STATE} during execution). E.g., they would try to code |
|
@code{foobar} like this: |
|
|
|
@example |
|
: foobar |
|
STATE @@ |
|
IF ( compilation state ) |
|
POSTPONE foo POSTPONE bar |
|
ELSE |
|
foo bar |
|
ENDIF ; immediate |
|
@end example |
|
|
|
While this works if @code{foobar} is processed only by the text |
|
interpreter, it does not work in other contexts (like @code{'} or |
|
@code{POSTPONE}). E.g., @code{' foobar} will produce an execution token |
|
for a state-smart word, not for the interpretation semantics of the |
|
original @code{foobar}; when you execute this execution token (directly |
|
with @code{EXECUTE} or indirectly through @code{COMPILE,}) in compile |
|
state, the result will not be what you expected (i.e., it will not |
|
perform @code{foo bar}). State-smart words are a bad idea. Simply don't |
|
write them! |
|
|
|
@cindex defining words with arbitrary semantics combinations |
|
It is also possible to write defining words that define words with |
|
arbitrary combinations of interpretation and compilation semantics (or, |
|
preferably, arbitrary combinations of implementations of the default |
|
semantics). In general, this looks like: |
|
|
|
@example |
|
: def-word |
|
create-interpret/compile |
|
@var{code1} |
|
interpretation> |
|
@var{code2} |
|
<interpretation |
|
compilation> |
|
@var{code3} |
|
<compilation ; |
|
@end example |
|
|
|
For a @var{word} defined with @code{def-word}, the interpretation |
|
semantics are to push the address of the body of @var{word} and perform |
|
@var{code2}, and the compilation semantics are to push the address of |
|
the body of @var{word} and perform @var{code3}. E.g., @code{constant} |
|
can also be defined like this: |
|
|
|
@example |
|
: constant ( n "name" -- ) |
|
create-interpret/compile |
|
, |
|
interpretation> ( -- n ) |
|
@@ |
|
<interpretation |
|
compilation> ( compilation. -- ; run-time. -- n ) |
|
@@ postpone literal |
|
<compilation ; |
|
@end example |
|
|
|
doc-create-interpret/compile |
|
doc-interpretation> |
|
doc-<interpretation |
|
doc-compilation> |
|
doc-<compilation |
|
|
|
Note that words defined with @code{interpret/compile:} and |
|
@code{create-interpret/compile} have an extended header structure that |
|
differs from other words; however, unless you try to access them with |
|
plain address arithmetic, you should not notice this. Words for |
|
accessing the header structure usually know how to deal with this; e.g., |
|
@code{' word >body} also gives you the body of a word created with |
|
@code{create-interpret/compile}. |
|
|
|
@node Tokens for Words, Wordlists, Defining Words, Words |
|
@section Tokens for Words |
|
@cindex tokens for words |
|
|
|
This chapter describes the creation and use of tokens that represent |
|
words on the stack (and in data space). |
|
|
|
Named words have interpretation and compilation semantics. Unnamed words |
|
just have execution semantics. |
|
|
|
@cindex execution token |
|
An @dfn{execution token} represents the execution semantics of an |
|
unnamed word. An execution token occupies one cell. As explained in |
|
section @ref{Supplying names}, the execution token of the last words |
|
defined can be produced with |
|
|
|
short-lastxt |
|
|
|
You can perform the semantics represented by an execution token with |
|
doc-execute |
|
You can compile the word with |
|
doc-compile, |
|
|
|
@cindex code field address |
|
@cindex CFA |
|
In Gforth, the abstract data type @emph{execution token} is implemented |
|
as CFA (code field address). |
|
|
|
The interpretation semantics of a named word are also represented by an |
|
execution token. You can get it with |
|
|
|
doc-['] |
|
doc-' |
|
|
|
For literals, you use @code{'} in interpreted code and @code{[']} in |
|
compiled code. Gforth's @code{'} and @code{[']} behave somewhat unusual |
|
by complaining about compile-only words. To get an execution token for a |
|
compiling word @var{X}, use @code{COMP' @var{X} drop} or @code{[COMP'] |
|
@var{X} drop}. |
|
|
|
@cindex compilation token |
|
The compilation semantics are represented by a @dfn{compilation token} |
|
consisting of two cells: @var{w xt}. The top cell @var{xt} is an |
|
execution token. The compilation semantics represented by the |
|
compilation token can be performed with @code{execute}, which consumes |
|
the whole compilation token, with an additional stack effect determined |
|
by the represented compilation semantics. |
|
|
|
doc-[comp'] |
|
doc-comp' |
|
|
|
You can compile the compilation semantics with @code{postpone,}. I.e., |
|
@code{COMP' @var{word} POSTPONE,} is equivalent to @code{POSTPONE |
|
@var{word}}. |
|
|
|
doc-postpone, |
|
|
|
At present, the @var{w} part of a compilation token is an execution |
|
token, and the @var{xt} part represents either @code{execute} or |
|
@code{compile,}. However, don't rely on that knowledge, unless necessary; |
|
we may introduce unusual compilation tokens in the future (e.g., |
|
compilation tokens representing the compilation semantics of literals). |
|
|
|
@cindex name token |
|
@cindex name field address |
|
@cindex NFA |
|
Named words are also represented by the @dfn{name token}. The abstract |
|
data type @emph{name token} is implemented as NFA (name field address). |
|
|
|
doc-find-name |
|
doc-name>int |
|
doc-name?int |
|
doc-name>comp |
|
doc-name>string |
|
|
|
@node Wordlists, Files, Tokens for Words, Words |
|
@section Wordlists |
|
|
|
@node Files, Blocks, Wordlists, Words |
|
@section Files |
|
|
|
@node Blocks, Other I/O, Files, Words |
|
@section Blocks |
|
|
|
@node Other I/O, Programming Tools, Blocks, Words |
|
@section Other I/O |
|
|
|
@node Programming Tools, Assembler and Code words, Other I/O, Words |
|
@section Programming Tools |
|
@cindex programming tools |
|
|
|
@menu |
|
* Debugging:: Simple and quick. |
|
* Assertions:: Making your programs self-checking. |
|
@end menu |
|
|
|
@node Debugging, Assertions, Programming Tools, Programming Tools |
|
@subsection Debugging |
|
@cindex debugging |
|
|
|
The simple debugging aids provided in @file{debugging.fs} |
|
are meant to support a different style of debugging than the |
|
tracing/stepping debuggers used in languages with long turn-around |
|
times. |
|
|
|
A much better (faster) way in fast-compiling languages is to add |
|
printing code at well-selected places, let the program run, look at |
|
the output, see where things went wrong, add more printing code, etc., |
|
until the bug is found. |
|
|
|
The word @code{~~} is easy to insert. It just prints debugging |
|
information (by default the source location and the stack contents). It |
|
is also easy to remove (@kbd{C-x ~} in the Emacs Forth mode to |
|
query-replace them with nothing). The deferred words |
|
@code{printdebugdata} and @code{printdebugline} control the output of |
|
@code{~~}. The default source location output format works well with |
|
Emacs' compilation mode, so you can step through the program at the |
|
source level using @kbd{C-x `} (the advantage over a stepping debugger |
|
is that you can step in any direction and you know where the crash has |
|
happened or where the strange data has occurred). |
|
|
|
Note that the default actions clobber the contents of the pictured |
|
numeric output string, so you should not use @code{~~}, e.g., between |
|
@code{<#} and @code{#>}. |
|
|
|
doc-~~ |
|
doc-printdebugdata |
|
doc-printdebugline |
|
|
|
@node Assertions, , Debugging, Programming Tools |
|
@subsection Assertions |
|
@cindex assertions |
|
|
|
It is a good idea to make your programs self-checking, in particular, if |
|
you use an assumption (e.g., that a certain field of a data structure is |
|
never zero) that may become wrong during maintenance. Gforth supports |
|
assertions for this purpose. They are used like this: |
|
|
|
@example |
|
assert( @var{flag} ) |
|
@end example |
|
|
|
The code between @code{assert(} and @code{)} should compute a flag, that |
|
should be true if everything is alright and false otherwise. It should |
|
not change anything else on the stack. The overall stack effect of the |
|
assertion is @code{( -- )}. E.g. |
|
|
|
@example |
|
assert( 1 1 + 2 = ) \ what we learn in school |
|
assert( dup 0<> ) \ assert that the top of stack is not zero |
|
assert( false ) \ this code should not be reached |
|
@end example |
|
|
|
The need for assertions is different at different times. During |
|
debugging, we want more checking, in production we sometimes care more |
|
for speed. Therefore, assertions can be turned off, i.e., the assertion |
|
becomes a comment. Depending on the importance of an assertion and the |
|
time it takes to check it, you may want to turn off some assertions and |
|
keep others turned on. Gforth provides several levels of assertions for |
|
this purpose: |
|
|
|
doc-assert0( |
|
doc-assert1( |
|
doc-assert2( |
|
doc-assert3( |
|
doc-assert( |
|
doc-) |
|
|
|
@code{Assert(} is the same as @code{assert1(}. The variable |
|
@code{assert-level} specifies the highest assertions that are turned |
|
on. I.e., at the default @code{assert-level} of one, @code{assert0(} and |
|
@code{assert1(} assertions perform checking, while @code{assert2(} and |
|
@code{assert3(} assertions are treated as comments. |
|
|
|
Note that the @code{assert-level} is evaluated at compile-time, not at |
|
run-time. I.e., you cannot turn assertions on or off at run-time, you |
|
have to set the @code{assert-level} appropriately before compiling a |
|
piece of code. You can compile several pieces of code at several |
|
@code{assert-level}s (e.g., a trusted library at level 1 and newly |
|
written code at level 3). |
|
|
|
doc-assert-level |
|
|
|
If an assertion fails, a message compatible with Emacs' compilation mode |
|
is produced and the execution is aborted (currently with @code{ABORT"}. |
|
If there is interest, we will introduce a special throw code. But if you |
|
intend to @code{catch} a specific condition, using @code{throw} is |
|
probably more appropriate than an assertion). |
|
|
|
@node Assembler and Code words, Threading Words, Programming Tools, Words |
|
@section Assembler and Code words |
|
@cindex assembler |
|
@cindex code words |
|
|
|
Gforth provides some words for defining primitives (words written in |
|
machine code), and for defining the the machine-code equivalent of |
|
@code{DOES>}-based defining words. However, the machine-independent |
|
nature of Gforth poses a few problems: First of all, Gforth runs on |
|
several architectures, so it can provide no standard assembler. What's |
|
worse is that the register allocation not only depends on the processor, |
|
but also on the @code{gcc} version and options used. |
|
|
|
The words that Gforth offers encapsulate some system dependences (e.g., the |
|
header structure), so a system-independent assembler may be used in |
|
Gforth. If you do not have an assembler, you can compile machine code |
|
directly with @code{,} and @code{c,}. |
|
|
|
doc-assembler |
|
doc-code |
|
doc-end-code |
|
doc-;code |
|
doc-flush-icache |
|
|
|
If @code{flush-icache} does not work correctly, @code{code} words |
|
etc. will not work (reliably), either. |
|
|
|
These words are rarely used. Therefore they reside in @code{code.fs}, |
|
which is usually not loaded (except @code{flush-icache}, which is always |
|
present). You can load them with @code{require code.fs}. |
|
|
|
@cindex registers of the inner interpreter |
|
In the assembly code you will want to refer to the inner interpreter's |
|
registers (e.g., the data stack pointer) and you may want to use other |
|
registers for temporary storage. Unfortunately, the register allocation |
|
is installation-dependent. |
|
|
|
The easiest solution is to use explicit register declarations |
|
(@pxref{Explicit Reg Vars, , Variables in Specified Registers, gcc.info, |
|
GNU C Manual}) for all of the inner interpreter's registers: You have to |
|
compile Gforth with @code{-DFORCE_REG} (configure option |
|
@code{--enable-force-reg}) and the appropriate declarations must be |
|
present in the @code{machine.h} file (see @code{mips.h} for an example; |
|
you can find a full list of all declarable register symbols with |
|
@code{grep register engine.c}). If you give explicit registers to all |
|
variables that are declared at the beginning of @code{engine()}, you |
|
should be able to use the other caller-saved registers for temporary |
|
storage. Alternatively, you can use the @code{gcc} option |
|
@code{-ffixed-REG} (@pxref{Code Gen Options, , Options for Code |
|
Generation Conventions, gcc.info, GNU C Manual}) to reserve a register |
|
(however, this restriction on register allocation may slow Gforth |
|
significantly). |
|
|
|
If this solution is not viable (e.g., because @code{gcc} does not allow |
|
you to explicitly declare all the registers you need), you have to find |
|
out by looking at the code where the inner interpreter's registers |
|
reside and which registers can be used for temporary storage. You can |
|
get an assembly listing of the engine's code with @code{make engine.s}. |
|
|
|
In any case, it is good practice to abstract your assembly code from the |
|
actual register allocation. E.g., if the data stack pointer resides in |
|
register @code{$17}, create an alias for this register called @code{sp}, |
|
and use that in your assembly code. |
|
|
|
@cindex code words, portable |
|
Another option for implementing normal and defining words efficiently |
|
is: adding the wanted functionality to the source of Gforth. For normal |
|
words you just have to edit @file{primitives} (@pxref{Automatic |
|
Generation}), defining words (equivalent to @code{;CODE} words, for fast |
|
defined words) may require changes in @file{engine.c}, @file{kernal.fs}, |
|
@file{prims2x.fs}, and possibly @file{cross.fs}. |
|
|
|
|
|
@node Threading Words, , Assembler and Code words, Words |
|
@section Threading Words |
|
@cindex threading words |
|
|
|
@cindex code address |
|
These words provide access to code addresses and other threading stuff |
|
in Gforth (and, possibly, other interpretive Forths). It more or less |
|
abstracts away the differences between direct and indirect threading |
|
(and, for direct threading, the machine dependences). However, at |
|
present this wordset is still incomplete. It is also pretty low-level; |
|
some day it will hopefully be made unnecessary by an internals wordset |
|
that abstracts implementation details away completely. |
|
|
|
doc->code-address |
|
doc->does-code |
|
doc-code-address! |
|
doc-does-code! |
|
doc-does-handler! |
|
doc-/does-handler |
|
|
|
The code addresses produced by various defining words are produced by |
|
the following words: |
|
|
|
doc-docol: |
|
doc-docon: |
|
doc-dovar: |
|
doc-douser: |
|
doc-dodefer: |
|
doc-dofield: |
|
|
|
You can recognize words defined by a @code{CREATE}...@code{DOES>} word |
|
with @code{>DOES-CODE}. If the word was defined in that way, the value |
|
returned is different from 0 and identifies the @code{DOES>} used by the |
|
defining word. |
|
|
|
@node Tools, ANS conformance, Words, Top |
|
@chapter Tools |
|
|
|
@menu |
|
* ANS Report:: Report the words used, sorted by wordset. |
|
@end menu |
|
|
|
See also @ref{Emacs and Gforth}. |
|
|
|
@node ANS Report, , Tools, Tools |
|
@section @file{ans-report.fs}: Report the words used, sorted by wordset |
|
@cindex @file{ans-report.fs} |
|
@cindex report the words used in your program |
|
@cindex words used in your program |
|
|
|
If you want to label a Forth program as ANS Forth Program, you must |
|
document which wordsets the program uses; for extension wordsets, it is |
|
helpful to list the words the program requires from these wordsets |
|
(because Forth systems are allowed to provide only some words of them). |
|
|
|
The @file{ans-report.fs} tool makes it easy for you to determine which |
|
words from which wordset and which non-ANS words your application |
|
uses. You simply have to include @file{ans-report.fs} before loading the |
|
program you want to check. After loading your program, you can get the |
|
report with @code{print-ans-report}. A typical use is to run this as |
|
batch job like this: |
|
@example |
|
gforth ans-report.fs myprog.fs -e "print-ans-report bye" |
|
@end example |
|
|
|
The output looks like this (for @file{compat/control.fs}): |
|
@example |
|
The program uses the following words |
|
from CORE : |
|
: POSTPONE THEN ; immediate ?dup IF 0= |
|
from BLOCK-EXT : |
|
\ |
|
from FILE : |
|
( |
|
@end example |
|
|
|
@subsection Caveats |
|
|
|
Note that @file{ans-report.fs} just checks which words are used, not whether |
|
they are used in an ANS Forth conforming way! |
|
|
|
Some words are defined in several wordsets in the |
|
standard. @file{ans-report.fs} reports them for only one of the |
|
wordsets, and not necessarily the one you expect. It depends on usage |
|
which wordset is the right one to specify. E.g., if you only use the |
|
compilation semantics of @code{S"}, it is a Core word; if you also use |
|
its interpretation semantics, it is a File word. |
|
|
|
@c ****************************************************************** |
|
@node ANS conformance, Model, Tools, Top |
|
@chapter ANS conformance |
|
@cindex ANS conformance of Gforth |
|
|
|
To the best of our knowledge, Gforth is an |
|
|
|
ANS Forth System |
|
@itemize @bullet |
|
@item providing the Core Extensions word set |
|
@item providing the Block word set |
|
@item providing the Block Extensions word set |
|
@item providing the Double-Number word set |
|
@item providing the Double-Number Extensions word set |
|
@item providing the Exception word set |
|
@item providing the Exception Extensions word set |
|
@item providing the Facility word set |
|
@item providing @code{MS} and @code{TIME&DATE} from the Facility Extensions word set |
|
@item providing the File Access word set |
|
@item providing the File Access Extensions word set |
|
@item providing the Floating-Point word set |
|
@item providing the Floating-Point Extensions word set |
|
@item providing the Locals word set |
|
@item providing the Locals Extensions word set |
|
@item providing the Memory-Allocation word set |
|
@item providing the Memory-Allocation Extensions word set (that one's easy) |
|
@item providing the Programming-Tools word set |
|
@item providing @code{;CODE}, @code{AHEAD}, @code{ASSEMBLER}, @code{BYE}, @code{CODE}, @code{CS-PICK}, @code{CS-ROLL}, @code{STATE}, @code{[ELSE]}, @code{[IF]}, @code{[THEN]} from the Programming-Tools Extensions word set |
|
@item providing the Search-Order word set |
|
@item providing the Search-Order Extensions word set |
|
@item providing the String word set |
|
@item providing the String Extensions word set (another easy one) |
|
@end itemize |
|
|
|
@cindex system documentation |
|
In addition, ANS Forth systems are required to document certain |
|
implementation choices. This chapter tries to meet these |
|
requirements. In many cases it gives a way to ask the system for the |
|
information instead of providing the information directly, in |
|
particular, if the information depends on the processor, the operating |
|
system or the installation options chosen, or if they are likely to |
|
change during the maintenance of Gforth. |
|
|
|
@comment The framework for the rest has been taken from pfe. |
|
|
|
@menu |
|
* The Core Words:: |
|
* The optional Block word set:: |
|
* The optional Double Number word set:: |
|
* The optional Exception word set:: |
|
* The optional Facility word set:: |
|
* The optional File-Access word set:: |
|
* The optional Floating-Point word set:: |
|
* The optional Locals word set:: |
|
* The optional Memory-Allocation word set:: |
|
* The optional Programming-Tools word set:: |
|
* The optional Search-Order word set:: |
|
@end menu |
|
|
|
|
|
@c ===================================================================== |
|
@node The Core Words, The optional Block word set, ANS conformance, ANS conformance |
|
@comment node-name, next, previous, up |
|
@section The Core Words |
|
@c ===================================================================== |
|
@cindex core words, system documentation |
|
@cindex system documentation, core words |
|
|
|
@menu |
|
* core-idef:: Implementation Defined Options |
|
* core-ambcond:: Ambiguous Conditions |
|
* core-other:: Other System Documentation |
|
@end menu |
|
|
|
@c --------------------------------------------------------------------- |
|
@node core-idef, core-ambcond, The Core Words, The Core Words |
|
@subsection Implementation Defined Options |
|
@c --------------------------------------------------------------------- |
|
@cindex core words, implementation-defined options |
|
@cindex implementation-defined options, core words |
|
|
|
|
|
@table @i |
|
@item (Cell) aligned addresses: |
|
@cindex cell-aligned addresses |
|
@cindex aligned addresses |
|
processor-dependent. Gforth's alignment words perform natural alignment |
|
(e.g., an address aligned for a datum of size 8 is divisible by |
|
8). Unaligned accesses usually result in a @code{-23 THROW}. |
|
|
|
@item @code{EMIT} and non-graphic characters: |
|
@cindex @code{EMIT} and non-graphic characters |
|
@cindex non-graphic characters and @code{EMIT} |
|
The character is output using the C library function (actually, macro) |
|
@code{putc}. |
|
|
|
@item character editing of @code{ACCEPT} and @code{EXPECT}: |
|
@cindex character editing of @code{ACCEPT} and @code{EXPECT} |
|
@cindex editing in @code{ACCEPT} and @code{EXPECT} |
|
@cindex @code{ACCEPT}, editing |
|
@cindex @code{EXPECT}, editing |
|
This is modeled on the GNU readline library (@pxref{Readline |
|
Interaction, , Command Line Editing, readline, The GNU Readline |
|
Library}) with Emacs-like key bindings. @kbd{Tab} deviates a little by |
|
producing a full word completion every time you type it (instead of |
|
producing the common prefix of all completions). |
|
|
|
@item character set: |
|
@cindex character set |
|
The character set of your computer and display device. Gforth is |
|
8-bit-clean (but some other component in your system may make trouble). |
|
|
|
@item Character-aligned address requirements: |
|
@cindex character-aligned address requirements |
|
installation-dependent. Currently a character is represented by a C |
|
@code{unsigned char}; in the future we might switch to @code{wchar_t} |
|
(Comments on that requested). |
|
|
|
@item character-set extensions and matching of names: |
|
@cindex character-set extensions and matching of names |
|
@cindex case sensitivity for name lookup |
|
@cindex name lookup, case sensitivity |
|
@cindex locale and case sensitivity |
|
Any character except the ASCII NUL charcter can be used in a |
|
name. Matching is case-insensitive (except in @code{TABLE}s). The |
|
matching is performed using the C function @code{strncasecmp}, whose |
|
function is probably influenced by the locale. E.g., the @code{C} locale |
|
does not know about accents and umlauts, so they are matched |
|
case-sensitively in that locale. For portability reasons it is best to |
|
write programs such that they work in the @code{C} locale. Then one can |
|
use libraries written by a Polish programmer (who might use words |
|
containing ISO Latin-2 encoded characters) and by a French programmer |
|
(ISO Latin-1) in the same program (of course, @code{WORDS} will produce |
|
funny results for some of the words (which ones, depends on the font you |
|
are using)). Also, the locale you prefer may not be available in other |
|
operating systems. Hopefully, Unicode will solve these problems one day. |
|
|
|
@item conditions under which control characters match a space delimiter: |
|
@cindex space delimiters |
|
@cindex control characters as delimiters |
|
If @code{WORD} is called with the space character as a delimiter, all |
|
white-space characters (as identified by the C macro @code{isspace()}) |
|
are delimiters. @code{PARSE}, on the other hand, treats space like other |
|
delimiters. @code{PARSE-WORD} treats space like @code{WORD}, but behaves |
|
like @code{PARSE} otherwise. @code{(NAME)}, which is used by the outer |
|
interpreter (aka text interpreter) by default, treats all white-space |
|
characters as delimiters. |
|
|
|
@item format of the control flow stack: |
|
@cindex control flow stack, format |
|
The data stack is used as control flow stack. The size of a control flow |
|
stack item in cells is given by the constant @code{cs-item-size}. At the |
|
time of this writing, an item consists of a (pointer to a) locals list |
|
(third), an address in the code (second), and a tag for identifying the |
|
item (TOS). The following tags are used: @code{defstart}, |
|
@code{live-orig}, @code{dead-orig}, @code{dest}, @code{do-dest}, |
|
@code{scopestart}. |
|
|
|
@item conversion of digits > 35 |
|
@cindex digits > 35 |
|
The characters @code{[\]^_'} are the digits with the decimal value |
|
36@minus{}41. There is no way to input many of the larger digits. |
|
|
|
@item display after input terminates in @code{ACCEPT} and @code{EXPECT}: |
|
@cindex @code{EXPECT}, display after end of input |
|
@cindex @code{ACCEPT}, display after end of input |
|
The cursor is moved to the end of the entered string. If the input is |
|
terminated using the @kbd{Return} key, a space is typed. |
|
|
|
@item exception abort sequence of @code{ABORT"}: |
|
@cindex exception abort sequence of @code{ABORT"} |
|
@cindex @code{ABORT"}, exception abort sequence |
|
The error string is stored into the variable @code{"error} and a |
|
@code{-2 throw} is performed. |
|
|
|
@item input line terminator: |
|
@cindex input line terminator |
|
@cindex line terminator on input |
|
@cindex newline charcter on input |
|
For interactive input, @kbd{C-m} (CR) and @kbd{C-j} (LF) terminate |
|
lines. One of these characters is typically produced when you type the |
|
@kbd{Enter} or @kbd{Return} key. |
|
|
|
@item maximum size of a counted string: |
|
@cindex maximum size of a counted string |
|
@cindex counted string, maximum size |
|
@code{s" /counted-string" environment? drop .}. Currently 255 characters |
|
on all ports, but this may change. |
|
|
|
@item maximum size of a parsed string: |
|
@cindex maximum size of a parsed string |
|
@cindex parsed string, maximum size |
|
Given by the constant @code{/line}. Currently 255 characters. |
|
|
|
@item maximum size of a definition name, in characters: |
|
@cindex maximum size of a definition name, in characters |
|
@cindex name, maximum length |
|
31 |
|
|
|
@item maximum string length for @code{ENVIRONMENT?}, in characters: |
|
@cindex maximum string length for @code{ENVIRONMENT?}, in characters |
|
@cindex @code{ENVIRONMENT?} string length, maximum |
|
31 |
|
|
|
@item method of selecting the user input device: |
|
@cindex user input device, method of selecting |
|
The user input device is the standard input. There is currently no way to |
|
change it from within Gforth. However, the input can typically be |
|
redirected in the command line that starts Gforth. |
|
|
|
@item method of selecting the user output device: |
|
@cindex user output device, method of selecting |
|
@code{EMIT} and @code{TYPE} output to the file-id stored in the value |
|
@code{outfile-id} (@code{stdout} by default). Gforth uses buffered |
|
output, so output on a terminal does not become visible before the next |
|
newline or buffer overflow. Output on non-terminals is invisible until |
|
the buffer overflows. |
|
|
|
@item methods of dictionary compilation: |
|
What are we expected to document here? |
|
|
|
@item number of bits in one address unit: |
|
@cindex number of bits in one address unit |
|
@cindex address unit, size in bits |
|
@code{s" address-units-bits" environment? drop .}. 8 in all current |
|
ports. |
|
|
|
@item number representation and arithmetic: |
|
@cindex number representation and arithmetic |
|
Processor-dependent. Binary two's complement on all current ports. |
|
|
|
@item ranges for integer types: |
|
@cindex ranges for integer types |
|
@cindex integer types, ranges |
|
Installation-dependent. Make environmental queries for @code{MAX-N}, |
|
@code{MAX-U}, @code{MAX-D} and @code{MAX-UD}. The lower bounds for |
|
unsigned (and positive) types is 0. The lower bound for signed types on |
|
two's complement and one's complement machines machines can be computed |
|
by adding 1 to the upper bound. |
|
|
|
@item read-only data space regions: |
|
@cindex read-only data space regions |
|
@cindex data-space, read-only regions |
|
The whole Forth data space is writable. |
|
|
|
@item size of buffer at @code{WORD}: |
|
@cindex size of buffer at @code{WORD} |
|
@cindex @code{WORD} buffer size |
|
@code{PAD HERE - .}. 104 characters on 32-bit machines. The buffer is |
|
shared with the pictured numeric output string. If overwriting |
|
@code{PAD} is acceptable, it is as large as the remaining dictionary |
|
space, although only as much can be sensibly used as fits in a counted |
|
string. |
|
|
|
@item size of one cell in address units: |
|
@cindex cell size |
|
@code{1 cells .}. |
|
|
|
@item size of one character in address units: |
|
@cindex char size |
|
@code{1 chars .}. 1 on all current ports. |
|
|
|
@item size of the keyboard terminal buffer: |
|
@cindex size of the keyboard terminal buffer |
|
@cindex terminal buffer, size |
|
Varies. You can determine the size at a specific time using @code{lp@@ |
|
tib - .}. It is shared with the locals stack and TIBs of files that |
|
include the current file. You can change the amount of space for TIBs |
|
and locals stack at Gforth startup with the command line option |
|
@code{-l}. |
|
|
|
@item size of the pictured numeric output buffer: |
|
@cindex size of the pictured numeric output buffer |
|
@cindex pictured numeric output buffer, size |
|
@code{PAD HERE - .}. 104 characters on 32-bit machines. The buffer is |
|
shared with @code{WORD}. |
|
|
|
@item size of the scratch area returned by @code{PAD}: |
|
@cindex size of the scratch area returned by @code{PAD} |
|
@cindex @code{PAD} size |
|
The remainder of dictionary space. @code{unused pad here - - .}. |
|
|
|
@item system case-sensitivity characteristics: |
|
@cindex case-sensitivity characteristics |
|
Dictionary searches are case insensitive (except in |
|
@code{TABLE}s). However, as explained above under @i{character-set |
|
extensions}, the matching for non-ASCII characters is determined by the |
|
locale you are using. In the default @code{C} locale all non-ASCII |
|
characters are matched case-sensitively. |
|
|
|
@item system prompt: |
|
@cindex system prompt |
|
@cindex prompt |
|
@code{ ok} in interpret state, @code{ compiled} in compile state. |
|
|
|
@item division rounding: |
|
@cindex division rounding |
|
installation dependent. @code{s" floored" environment? drop .}. We leave |
|
the choice to @code{gcc} (what to use for @code{/}) and to you (whether |
|
to use @code{fm/mod}, @code{sm/rem} or simply @code{/}). |
|
|
|
@item values of @code{STATE} when true: |
|
@cindex @code{STATE} values |
|
-1. |
|
|
|
@item values returned after arithmetic overflow: |
|
On two's complement machines, arithmetic is performed modulo |
|
2**bits-per-cell for single arithmetic and 4**bits-per-cell for double |
|
arithmetic (with appropriate mapping for signed types). Division by zero |
|
typically results in a @code{-55 throw} (Floating-point unidentified |
|
fault), although a @code{-10 throw} (divide by zero) would be more |
|
appropriate. |
|
|
|
@item whether the current definition can be found after @t{DOES>}: |
|
@cindex @t{DOES>}, visibility of current definition |
|
No. |
|
|
|
@end table |
|
|
|
@c --------------------------------------------------------------------- |
|
@node core-ambcond, core-other, core-idef, The Core Words |
|
@subsection Ambiguous conditions |
|
@c --------------------------------------------------------------------- |
|
@cindex core words, ambiguous conditions |
|
@cindex ambiguous conditions, core words |
|
|
|
@table @i |
|
|
|
@item a name is neither a word nor a number: |
|
@cindex name not found |
|
@cindex Undefined word |
|
@code{-13 throw} (Undefined word). Actually, @code{-13 bounce}, which |
|
preserves the data and FP stack, so you don't lose more work than |
|
necessary. |
|
|
|
@item a definition name exceeds the maximum length allowed: |
|
@cindex Word name too long |
|
@code{-19 throw} (Word name too long) |
|
|
|
@item addressing a region not inside the various data spaces of the forth system: |
|
@cindex Invalid memory address |
|
The stacks, code space and name space are accessible. Machine code space is |
|
typically readable. Accessing other addresses gives results dependent on |
|
the operating system. On decent systems: @code{-9 throw} (Invalid memory |
|
address). |
|
|
|
@item argument type incompatible with parameter: |
|
@cindex Argument type mismatch |
|
This is usually not caught. Some words perform checks, e.g., the control |
|
flow words, and issue a @code{ABORT"} or @code{-12 THROW} (Argument type |
|
mismatch). |
|
|
|
@item attempting to obtain the execution token of a word with undefined execution semantics: |
|
@cindex Interpreting a compile-only word, for @code{'} etc. |
|
@cindex execution token of words with undefined execution semantics |
|
@code{-14 throw} (Interpreting a compile-only word). In some cases, you |
|
get an execution token for @code{compile-only-error} (which performs a |
|
@code{-14 throw} when executed). |
|
|
|
@item dividing by zero: |
|
@cindex dividing by zero |
|
@cindex floating point unidentified fault, integer division |
|
@cindex divide by zero |
|
typically results in a @code{-55 throw} (floating point unidentified |
|
fault), although a @code{-10 throw} (divide by zero) would be more |
|
appropriate. |
|
|
|
@item insufficient data stack or return stack space: |
|
@cindex insufficient data stack or return stack space |
|
@cindex stack overflow |
|
@cindex Address alignment exception, stack overflow |
|
@cindex Invalid memory address, stack overflow |
|
Depending on the operating system, the installation, and the invocation |
|
of Gforth, this is either checked by the memory management hardware, or |
|
it is not checked. If it is checked, you typically get a @code{-9 throw} |
|
(Invalid memory address) as soon as the overflow happens. If it is not |
|
check, overflows typically result in mysterious illegal memory accesses, |
|
producing @code{-9 throw} (Invalid memory address) or @code{-23 throw} |
|
(Address alignment exception); they might also destroy the internal data |
|
structure of @code{ALLOCATE} and friends, resulting in various errors in |
|
these words. |
|
|
|
@item insufficient space for loop control parameters: |
|
@cindex insufficient space for loop control parameters |
|
like other return stack overflows. |
|
|
|
@item insufficient space in the dictionary: |
|
@cindex insufficient space in the dictionary |
|
@cindex dictionary overflow |
|
Depending on the operating system, the installation, and the invocation |
|
of Gforth, this is either checked by the memory management hardware, or |
|
it is not checked. Similar results as stack overflows. However, |
|
typically the error appears at a different place when one inserts or |
|
removes code. Also, the @code{THROW} does not relieve the situation (it |
|
does for stack overflows). |
|
|
|
@item interpreting a word with undefined interpretation semantics: |
|
@cindex interpreting a word with undefined interpretation semantics |
|
@cindex Interpreting a compile-only word |
|
For some words, we have defined interpretation semantics. For the |
|
others: @code{-14 throw} (Interpreting a compile-only word). |
|
|
|
@item modifying the contents of the input buffer or a string literal: |
|
@cindex modifying the contents of the input buffer or a string literal |
|
These are located in writable memory and can be modified. |
|
|
|
@item overflow of the pictured numeric output string: |
|
@cindex overflow of the pictured numeric output string |
|
@cindex pictured numeric output string, overflow |
|
Not checked. Runs into the dictionary and destroys it (at least, |
|
partially). |
|
|
|
@item parsed string overflow: |
|
@cindex parsed string overflow |
|
@code{PARSE} cannot overflow. @code{WORD} does not check for overflow. |
|
|
|
@item producing a result out of range: |
|
@cindex result out of range |
|
On two's complement machines, arithmetic is performed modulo |
|
2**bits-per-cell for single arithmetic and 4**bits-per-cell for double |
|
arithmetic (with appropriate mapping for signed types). Division by zero |
|
typically results in a @code{-55 throw} (floatingpoint unidentified |
|
fault), although a @code{-10 throw} (divide by zero) would be more |
|
appropriate. @code{convert} and @code{>number} currently overflow |
|
silently. |
|
|
|
@item reading from an empty data or return stack: |
|
@cindex stack empty |
|
@cindex stack underflow |
|
The data stack is checked by the outer (aka text) interpreter after |
|
every word executed. If it has underflowed, a @code{-4 throw} (Stack |
|
underflow) is performed. Apart from that, stacks may be checked or not, |
|
depending on operating system, installation, and invocation. The |
|
consequences of stack underflows are similar to the consequences of |
|
stack overflows. Note that even if the system uses checking (through the |
|
MMU), your program may have to underflow by a significant number of |
|
stack items to trigger the reaction (the reason for this is that the |
|
MMU, and therefore the checking, works with a page-size granularity). |
|
|
|
@item unexpected end of the input buffer, resulting in an attempt to use a zero-length string as a name: |
|
@cindex unexpected end of the input buffer |
|
@cindex zero-length string as a name |
|
@cindex Attempt to use zero-length string as a name |
|
@code{Create} and its descendants perform a @code{-16 throw} (Attempt to |
|
use zero-length string as a name). Words like @code{'} probably will not |
|
find what they search. Note that it is possible to create zero-length |
|
names with @code{nextname} (should it not?). |
|
|
|
@item @code{>IN} greater than input buffer: |
|
@cindex @code{>IN} greater than input buffer |
|
The next invocation of a parsing word returns a string with length 0. |
|
|
|
@item @code{RECURSE} appears after @code{DOES>}: |
|
@cindex @code{RECURSE} appears after @code{DOES>} |
|
Compiles a recursive call to the defining word, not to the defined word. |
|
|
|
@item argument input source different than current input source for @code{RESTORE-INPUT}: |
|
@cindex argument input source different than current input source for @code{RESTORE-INPUT} |
|
@cindex Argument type mismatch, @code{RESTORE-INPUT} |
|
@cindex @code{RESTORE-INPUT}, Argument type mismatch |
|
@code{-12 THROW}. Note that, once an input file is closed (e.g., because |
|
the end of the file was reached), its source-id may be |
|
reused. Therefore, restoring an input source specification referencing a |
|
closed file may lead to unpredictable results instead of a @code{-12 |
|
THROW}. |
|
|
|
In the future, Gforth may be able to restore input source specifications |
|
from other than the current input source. |
|
|
|
@item data space containing definitions gets de-allocated: |
|
@cindex data space containing definitions gets de-allocated |
|
Deallocation with @code{allot} is not checked. This typically results in |
|
memory access faults or execution of illegal instructions. |
|
|
|
@item data space read/write with incorrect alignment: |
|
@cindex data space read/write with incorrect alignment |
|
@cindex alignment faults |
|
@cindex Address alignment exception |
|
Processor-dependent. Typically results in a @code{-23 throw} (Address |
|
alignment exception). Under Linux on a 486 or later processor with |
|
alignment turned on, incorrect alignment results in a @code{-9 throw} |
|
(Invalid memory address). There are reportedly some processors with |
|
alignment restrictions that do not report them. |
|
|
|
@item data space pointer not properly aligned, @code{,}, @code{C,}: |
|
@cindex data space pointer not properly aligned, @code{,}, @code{C,} |
|
Like other alignment errors. |
|
|
|
@item less than u+2 stack items (@code{PICK} and @code{ROLL}): |
|
Like other stack underflows. |
|
|
|
@item loop control parameters not available: |
|
@cindex loop control parameters not available |
|
Not checked. The counted loop words simply assume that the top of return |
|
stack items are loop control parameters and behave accordingly. |
|
|
|
@item most recent definition does not have a name (@code{IMMEDIATE}): |
|
@cindex most recent definition does not have a name (@code{IMMEDIATE}) |
|
@cindex last word was headerless |
|
@code{abort" last word was headerless"}. |
|
|
|
@item name not defined by @code{VALUE} used by @code{TO}: |
|
@cindex name not defined by @code{VALUE} used by @code{TO} |
|
@cindex @code{TO} on non-@code{VALUE}s |
|
@cindex Invalid name argument, @code{TO} |
|
@code{-32 throw} (Invalid name argument) (unless name is a local or was |
|
defined by @code{CONSTANT}; in the latter case it just changes the constant). |
|
|
|
@item name not found (@code{'}, @code{POSTPONE}, @code{[']}, @code{[COMPILE]}): |
|
@cindex name not found (@code{'}, @code{POSTPONE}, @code{[']}, @code{[COMPILE]}) |
|
@cindex Undefined word, @code{'}, @code{POSTPONE}, @code{[']}, @code{[COMPILE]} |
|
@code{-13 throw} (Undefined word) |
|
|
|
@item parameters are not of the same type (@code{DO}, @code{?DO}, @code{WITHIN}): |
|
@cindex parameters are not of the same type (@code{DO}, @code{?DO}, @code{WITHIN}) |
|
Gforth behaves as if they were of the same type. I.e., you can predict |
|
the behaviour by interpreting all parameters as, e.g., signed. |
|
|
|
@item @code{POSTPONE} or @code{[COMPILE]} applied to @code{TO}: |
|
@cindex @code{POSTPONE} or @code{[COMPILE]} applied to @code{TO} |
|
Assume @code{: X POSTPONE TO ; IMMEDIATE}. @code{X} performs the |
|
compilation semantics of @code{TO}. |
|
|
|
@item String longer than a counted string returned by @code{WORD}: |
|
@cindex String longer than a counted string returned by @code{WORD} |
|
@cindex @code{WORD}, string overflow |
|
Not checked. The string will be ok, but the count will, of course, |
|
contain only the least significant bits of the length. |
|
|
|
@item u greater than or equal to the number of bits in a cell (@code{LSHIFT}, @code{RSHIFT}): |
|
@cindex @code{LSHIFT}, large shift counts |
|
@cindex @code{RSHIFT}, large shift counts |
|
Processor-dependent. Typical behaviours are returning 0 and using only |
|
the low bits of the shift count. |
|
|
|
@item word not defined via @code{CREATE}: |
|
@cindex @code{>BODY} of non-@code{CREATE}d words |
|
@code{>BODY} produces the PFA of the word no matter how it was defined. |
|
|
|
@cindex @code{DOES>} of non-@code{CREATE}d words |
|
@code{DOES>} changes the execution semantics of the last defined word no |
|
matter how it was defined. E.g., @code{CONSTANT DOES>} is equivalent to |
|
@code{CREATE , DOES>}. |
|
|
|
@item words improperly used outside @code{<#} and @code{#>}: |
|
Not checked. As usual, you can expect memory faults. |
|
|
|
@end table |
|
|
|
|
|
@c --------------------------------------------------------------------- |
|
@node core-other, , core-ambcond, The Core Words |
|
@subsection Other system documentation |
|
@c --------------------------------------------------------------------- |
|
@cindex other system documentation, core words |
|
@cindex core words, other system documentation |
|
|
|
@table @i |
|
@item nonstandard words using @code{PAD}: |
|
@cindex @code{PAD} use by nonstandard words |
|
None. |
|
|
|
@item operator's terminal facilities available: |
|
@cindex operator's terminal facilities available |
|
After processing the command line, Gforth goes into interactive mode, |
|
and you can give commands to Gforth interactively. The actual facilities |
|
available depend on how you invoke Gforth. |
|
|
|
@item program data space available: |
|
@cindex program data space available |
|
@cindex data space available |
|
@code{UNUSED .} gives the remaining dictionary space. The total |
|
dictionary space can be specified with the @code{-m} switch |
|
(@pxref{Invoking Gforth}) when Gforth starts up. |
|
|
|
@item return stack space available: |
|
@cindex return stack space available |
|
You can compute the total return stack space in cells with |
|
@code{s" RETURN-STACK-CELLS" environment? drop .}. You can specify it at |
|
startup time with the @code{-r} switch (@pxref{Invoking Gforth}). |
|
|
|
@item stack space available: |
|
@cindex stack space available |
|
You can compute the total data stack space in cells with |
|
@code{s" STACK-CELLS" environment? drop .}. You can specify it at |
|
startup time with the @code{-d} switch (@pxref{Invoking Gforth}). |
|
|
|
@item system dictionary space required, in address units: |
|
@cindex system dictionary space required, in address units |
|
Type @code{here forthstart - .} after startup. At the time of this |
|
writing, this gives 80080 (bytes) on a 32-bit system. |
|
@end table |
|
|
|
|
|
@c ===================================================================== |
|
@node The optional Block word set, The optional Double Number word set, The Core Words, ANS conformance |
|
@section The optional Block word set |
|
@c ===================================================================== |
|
@cindex system documentation, block words |
|
@cindex block words, system documentation |
|
|
|
@menu |
|
* block-idef:: Implementation Defined Options |
|
* block-ambcond:: Ambiguous Conditions |
|
* block-other:: Other System Documentation |
|
@end menu |
|
|
|
|
|
@c --------------------------------------------------------------------- |
|
@node block-idef, block-ambcond, The optional Block word set, The optional Block word set |
|
@subsection Implementation Defined Options |
|
@c --------------------------------------------------------------------- |
|
@cindex implementation-defined options, block words |
|
@cindex block words, implementation-defined options |
|
|
|
@table @i |
|
@item the format for display by @code{LIST}: |
|
@cindex @code{LIST} display format |
|
First the screen number is displayed, then 16 lines of 64 characters, |
|
each line preceded by the line number. |
|
|
|
@item the length of a line affected by @code{\}: |
|
@cindex length of a line affected by @code{\} |
|
@cindex @code{\}, line length in blocks |
|
64 characters. |
|
@end table |
|
|
|
|
|
@c --------------------------------------------------------------------- |
|
@node block-ambcond, block-other, block-idef, The optional Block word set |
|
@subsection Ambiguous conditions |
|
@c --------------------------------------------------------------------- |
|
@cindex block words, ambiguous conditions |
|
@cindex ambiguous conditions, block words |
|
|
|
@table @i |
|
@item correct block read was not possible: |
|
@cindex block read not possible |
|
Typically results in a @code{throw} of some OS-derived value (between |
|
-512 and -2048). If the blocks file was just not long enough, blanks are |
|
supplied for the missing portion. |
|
|
|
@item I/O exception in block transfer: |
|
@cindex I/O exception in block transfer |
|
@cindex block transfer, I/O exception |
|
Typically results in a @code{throw} of some OS-derived value (between |
|
-512 and -2048). |
|
|
|
@item invalid block number: |
|
@cindex invalid block number |
|
@cindex block number invalid |
|
@code{-35 throw} (Invalid block number) |
|
|
|
@item a program directly alters the contents of @code{BLK}: |
|
@cindex @code{BLK}, altering @code{BLK} |
|
The input stream is switched to that other block, at the same |
|
position. If the storing to @code{BLK} happens when interpreting |
|
non-block input, the system will get quite confused when the block ends. |
|
|
|
@item no current block buffer for @code{UPDATE}: |
|
@cindex @code{UPDATE}, no current block buffer |
|
@code{UPDATE} has no effect. |
|
|
|
@end table |
|
|
|
@c --------------------------------------------------------------------- |
|
@node block-other, , block-ambcond, The optional Block word set |
|
@subsection Other system documentation |
|
@c --------------------------------------------------------------------- |
|
@cindex other system documentation, block words |
|
@cindex block words, other system documentation |
|
|
|
@table @i |
|
@item any restrictions a multiprogramming system places on the use of buffer addresses: |
|
No restrictions (yet). |
|
|
|
@item the number of blocks available for source and data: |
|
depends on your disk space. |
|
|
|
@end table |
|
|
|
|
|
@c ===================================================================== |
|
@node The optional Double Number word set, The optional Exception word set, The optional Block word set, ANS conformance |
|
@section The optional Double Number word set |
|
@c ===================================================================== |
|
@cindex system documentation, double words |
|
@cindex double words, system documentation |
|
|
|
@menu |
|
* double-ambcond:: Ambiguous Conditions |
|
@end menu |
|
|
|
|
|
@c --------------------------------------------------------------------- |
|
@node double-ambcond, , The optional Double Number word set, The optional Double Number word set |
|
@subsection Ambiguous conditions |
|
@c --------------------------------------------------------------------- |
|
@cindex double words, ambiguous conditions |
|
@cindex ambiguous conditions, double words |
|
|
|
@table @i |
|
@item @var{d} outside of range of @var{n} in @code{D>S}: |
|
@cindex @code{D>S}, @var{d} out of range of @var{n} |
|
The least significant cell of @var{d} is produced. |
|
|
|
@end table |
|
|
|
|
|
@c ===================================================================== |
|
@node The optional Exception word set, The optional Facility word set, The optional Double Number word set, ANS conformance |
|
@section The optional Exception word set |
|
@c ===================================================================== |
|
@cindex system documentation, exception words |
|
@cindex exception words, system documentation |
|
|
|
@menu |
|
* exception-idef:: Implementation Defined Options |
|
@end menu |
|
|
|
|
|
@c --------------------------------------------------------------------- |
|
@node exception-idef, , The optional Exception word set, The optional Exception word set |
|
@subsection Implementation Defined Options |
|
@c --------------------------------------------------------------------- |
|
@cindex implementation-defined options, exception words |
|
@cindex exception words, implementation-defined options |
|
|
|
@table @i |
|
@item @code{THROW}-codes used in the system: |
|
@cindex @code{THROW}-codes used in the system |
|
The codes -256@minus{}-511 are used for reporting signals. The mapping |
|
from OS signal numbers to throw codes is -256@minus{}@var{signal}. The |
|
codes -512@minus{}-2047 are used for OS errors (for file and memory |
|
allocation operations). The mapping from OS error numbers to throw codes |
|
is -512@minus{}@code{errno}. One side effect of this mapping is that |
|
undefined OS errors produce a message with a strange number; e.g., |
|
@code{-1000 THROW} results in @code{Unknown error 488} on my system. |
|
@end table |
|
|
|
@c ===================================================================== |
|
@node The optional Facility word set, The optional File-Access word set, The optional Exception word set, ANS conformance |
|
@section The optional Facility word set |
|
@c ===================================================================== |
|
@cindex system documentation, facility words |
|
@cindex facility words, system documentation |
|
|
|
@menu |
|
* facility-idef:: Implementation Defined Options |
|
* facility-ambcond:: Ambiguous Conditions |
|
@end menu |
|
|
|
|
|
@c --------------------------------------------------------------------- |
|
@node facility-idef, facility-ambcond, The optional Facility word set, The optional Facility word set |
|
@subsection Implementation Defined Options |
|
@c --------------------------------------------------------------------- |
|
@cindex implementation-defined options, facility words |
|
@cindex facility words, implementation-defined options |
|
|
|
@table @i |
|
@item encoding of keyboard events (@code{EKEY}): |
|
@cindex keyboard events, encoding in @code{EKEY} |
|
@cindex @code{EKEY}, encoding of keyboard events |
|
Not yet implemented. |
|
|
|
@item duration of a system clock tick: |
|
@cindex duration of a system clock tick |
|
@cindex clock tick duration |
|
System dependent. With respect to @code{MS}, the time is specified in |
|
microseconds. How well the OS and the hardware implement this, is |
|
another question. |
|
|
|
@item repeatability to be expected from the execution of @code{MS}: |
|
@cindex repeatability to be expected from the execution of @code{MS} |
|
@cindex @code{MS}, repeatability to be expected |
|
System dependent. On Unix, a lot depends on load. If the system is |
|
lightly loaded, and the delay is short enough that Gforth does not get |
|
swapped out, the performance should be acceptable. Under MS-DOS and |
|
other single-tasking systems, it should be good. |
|
|
|
@end table |
|
|
|
|
|
@c --------------------------------------------------------------------- |
|
@node facility-ambcond, , facility-idef, The optional Facility word set |
|
@subsection Ambiguous conditions |
|
@c --------------------------------------------------------------------- |
|
@cindex facility words, ambiguous conditions |
|
@cindex ambiguous conditions, facility words |
|
|
|
@table @i |
|
@item @code{AT-XY} can't be performed on user output device: |
|
@cindex @code{AT-XY} can't be performed on user output device |
|
Largely terminal dependent. No range checks are done on the arguments. |
|
No errors are reported. You may see some garbage appearing, you may see |
|
simply nothing happen. |
|
|
|
@end table |
|
|
|
|
|
@c ===================================================================== |
|
@node The optional File-Access word set, The optional Floating-Point word set, The optional Facility word set, ANS conformance |
|
@section The optional File-Access word set |
|
@c ===================================================================== |
|
@cindex system documentation, file words |
|
@cindex file words, system documentation |
|
|
|
@menu |
|
* file-idef:: Implementation Defined Options |
|
* file-ambcond:: Ambiguous Conditions |
|
@end menu |
|
|
|
@c --------------------------------------------------------------------- |
|
@node file-idef, file-ambcond, The optional File-Access word set, The optional File-Access word set |
|
@subsection Implementation Defined Options |
|
@c --------------------------------------------------------------------- |
|
@cindex implementation-defined options, file words |
|
@cindex file words, implementation-defined options |
|
|
|
@table @i |
|
@item file access methods used: |
|
@cindex file access methods used |
|
@code{R/O}, @code{R/W} and @code{BIN} work as you would |
|
expect. @code{W/O} translates into the C file opening mode @code{w} (or |
|
@code{wb}): The file is cleared, if it exists, and created, if it does |
|
not (with both @code{open-file} and @code{create-file}). Under Unix |
|
@code{create-file} creates a file with 666 permissions modified by your |
|
umask. |
|
|
|
@item file exceptions: |
|
@cindex file exceptions |
|
The file words do not raise exceptions (except, perhaps, memory access |
|
faults when you pass illegal addresses or file-ids). |
|
|
|
@item file line terminator: |
|
@cindex file line terminator |
|
System-dependent. Gforth uses C's newline character as line |
|
terminator. What the actual character code(s) of this are is |
|
system-dependent. |
|
|
|
@item file name format: |
|
@cindex file name format |
|
System dependent. Gforth just uses the file name format of your OS. |
|
|
|
@item information returned by @code{FILE-STATUS}: |
|
@cindex @code{FILE-STATUS}, returned information |
|
@code{FILE-STATUS} returns the most powerful file access mode allowed |
|
for the file: Either @code{R/O}, @code{W/O} or @code{R/W}. If the file |
|
cannot be accessed, @code{R/O BIN} is returned. @code{BIN} is applicable |
|
along with the returned mode. |
|
|
|
@item input file state after an exception when including source: |
|
@cindex exception when including source |
|
All files that are left via the exception are closed. |
|
|
|
@item @var{ior} values and meaning: |
|
@cindex @var{ior} values and meaning |
|
The @var{ior}s returned by the file and memory allocation words are |
|
intended as throw codes. They typically are in the range |
|
-512@minus{}-2047 of OS errors. The mapping from OS error numbers to |
|
@var{ior}s is -512@minus{}@var{errno}. |
|
|
|
@item maximum depth of file input nesting: |
|
@cindex maximum depth of file input nesting |
|
@cindex file input nesting, maximum depth |
|
limited by the amount of return stack, locals/TIB stack, and the number |
|
of open files available. This should not give you troubles. |
|
|
|
@item maximum size of input line: |
|
@cindex maximum size of input line |
|
@cindex input line size, maximum |
|
@code{/line}. Currently 255. |
|
|
|
@item methods of mapping block ranges to files: |
|
@cindex mapping block ranges to files |
|
@cindex files containing blocks |
|
@cindex blocks in files |
|
By default, blocks are accessed in the file @file{blocks.fb} in the |
|
current working directory. The file can be switched with @code{USE}. |
|
|
|
@item number of string buffers provided by @code{S"}: |
|
@cindex @code{S"}, number of string buffers |
|
1 |
|
|
|
@item size of string buffer used by @code{S"}: |
|
@cindex @code{S"}, size of string buffer |
|
@code{/line}. currently 255. |
|
|
|
@end table |
|
|
|
@c --------------------------------------------------------------------- |
|
@node file-ambcond, , file-idef, The optional File-Access word set |
|
@subsection Ambiguous conditions |
|
@c --------------------------------------------------------------------- |
|
@cindex file words, ambiguous conditions |
|
@cindex ambiguous conditions, file words |
|
|
|
@table @i |
|
@item attempting to position a file outside its boundaries: |
|
@cindex @code{REPOSITION-FILE}, outside the file's boundaries |
|
@code{REPOSITION-FILE} is performed as usual: Afterwards, |
|
@code{FILE-POSITION} returns the value given to @code{REPOSITION-FILE}. |
|
|
|
@item attempting to read from file positions not yet written: |
|
@cindex reading from file positions not yet written |
|
End-of-file, i.e., zero characters are read and no error is reported. |
|
|
|
@item @var{file-id} is invalid (@code{INCLUDE-FILE}): |
|
@cindex @code{INCLUDE-FILE}, @var{file-id} is invalid |
|
An appropriate exception may be thrown, but a memory fault or other |
|
problem is more probable. |
|
|
|
@item I/O exception reading or closing @var{file-id} (@code{INCLUDE-FILE}, @code{INCLUDED}): |
|
@cindex @code{INCLUDE-FILE}, I/O exception reading or closing @var{file-id} |
|
@cindex @code{INCLUDED}, I/O exception reading or closing @var{file-id} |
|
The @var{ior} produced by the operation, that discovered the problem, is |
|
thrown. |
|
|
|
@item named file cannot be opened (@code{INCLUDED}): |
|
@cindex @code{INCLUDED}, named file cannot be opened |
|
The @var{ior} produced by @code{open-file} is thrown. |
|
|
|
@item requesting an unmapped block number: |
|
@cindex unmapped block numbers |
|
There are no unmapped legal block numbers. On some operating systems, |
|
writing a block with a large number may overflow the file system and |
|
have an error message as consequence. |
|
|
|
@item using @code{source-id} when @code{blk} is non-zero: |
|
@cindex @code{SOURCE-ID}, behaviour when @code{BLK} is non-zero |
|
@code{source-id} performs its function. Typically it will give the id of |
|
the source which loaded the block. (Better ideas?) |
|
|
|
@end table |
|
|
|
|
|
@c ===================================================================== |
|
@node The optional Floating-Point word set, The optional Locals word set, The optional File-Access word set, ANS conformance |
|
@section The optional Floating-Point word set |
|
@c ===================================================================== |
|
@cindex system documentation, floating-point words |
|
@cindex floating-point words, system documentation |
|
|
|
@menu |
|
* floating-idef:: Implementation Defined Options |
|
* floating-ambcond:: Ambiguous Conditions |
|
@end menu |
|
|
|
|
|
@c --------------------------------------------------------------------- |
|
@node floating-idef, floating-ambcond, The optional Floating-Point word set, The optional Floating-Point word set |
|
@subsection Implementation Defined Options |
|
@c --------------------------------------------------------------------- |
|
@cindex implementation-defined options, floating-point words |
|
@cindex floating-point words, implementation-defined options |
|
|
|
@table @i |
|
@item format and range of floating point numbers: |
|
@cindex format and range of floating point numbers |
|
@cindex floating point numbers, format and range |
|
System-dependent; the @code{double} type of C. |
|
|
|
@item results of @code{REPRESENT} when @var{float} is out of range: |
|
@cindex @code{REPRESENT}, results when @var{float} is out of range |
|
System dependent; @code{REPRESENT} is implemented using the C library |
|
function @code{ecvt()} and inherits its behaviour in this respect. |
|
|
|
@item rounding or truncation of floating-point numbers: |
|
@cindex rounding of floating-point numbers |
|
@cindex truncation of floating-point numbers |
|
@cindex floating-point numbers, rounding or truncation |
|
System dependent; the rounding behaviour is inherited from the hosting C |
|
compiler. IEEE-FP-based (i.e., most) systems by default round to |
|
nearest, and break ties by rounding to even (i.e., such that the last |
|
bit of the mantissa is 0). |
|
|
|
@item size of floating-point stack: |
|
@cindex floating-point stack size |
|
@code{s" FLOATING-STACK" environment? drop .} gives the total size of |
|
the floating-point stack (in floats). You can specify this on startup |
|
with the command-line option @code{-f} (@pxref{Invoking Gforth}). |
|
|
|
@item width of floating-point stack: |
|
@cindex floating-point stack width |
|
@code{1 floats}. |
|
|
|
@end table |
|
|
|
|
|
@c --------------------------------------------------------------------- |
|
@node floating-ambcond, , floating-idef, The optional Floating-Point word set |
|
@subsection Ambiguous conditions |
|
@c --------------------------------------------------------------------- |
|
@cindex floating-point words, ambiguous conditions |
|
@cindex ambiguous conditions, floating-point words |
|
|
|
@table @i |
|
@item @code{df@@} or @code{df!} used with an address that is not double-float aligned: |
|
@cindex @code{df@@} or @code{df!} used with an address that is not double-float aligned |
|
System-dependent. Typically results in a @code{-23 THROW} like other |
|
alignment violations. |
|
|
|
@item @code{f@@} or @code{f!} used with an address that is not float aligned: |
|
@cindex @code{f@@} used with an address that is not float aligned |
|
@cindex @code{f!} used with an address that is not float aligned |
|
System-dependent. Typically results in a @code{-23 THROW} like other |
|
alignment violations. |
|
|
|
@item floating-point result out of range: |
|
@cindex floating-point result out of range |
|
System-dependent. Can result in a @code{-55 THROW} (Floating-point |
|
unidentified fault), or can produce a special value representing, e.g., |
|
Infinity. |
|
|
|
@item @code{sf@@} or @code{sf!} used with an address that is not single-float aligned: |
|
@cindex @code{sf@@} or @code{sf!} used with an address that is not single-float aligned |
|
System-dependent. Typically results in an alignment fault like other |
|
alignment violations. |
|
|
|
@item @code{BASE} is not decimal (@code{REPRESENT}, @code{F.}, @code{FE.}, @code{FS.}): |
|
@cindex @code{BASE} is not decimal (@code{REPRESENT}, @code{F.}, @code{FE.}, @code{FS.}) |
|
The floating-point number is converted into decimal nonetheless. |
|
|
|
@item Both arguments are equal to zero (@code{FATAN2}): |
|
@cindex @code{FATAN2}, both arguments are equal to zero |
|
System-dependent. @code{FATAN2} is implemented using the C library |
|
function @code{atan2()}. |
|
|
|
@item Using @code{FTAN} on an argument @var{r1} where cos(@var{r1}) is zero: |
|
@cindex @code{FTAN} on an argument @var{r1} where cos(@var{r1}) is zero |
|
System-dependent. Anyway, typically the cos of @var{r1} will not be zero |
|
because of small errors and the tan will be a very large (or very small) |
|
but finite number. |
|
|
|
@item @var{d} cannot be presented precisely as a float in @code{D>F}: |
|
@cindex @code{D>F}, @var{d} cannot be presented precisely as a float |
|
The result is rounded to the nearest float. |
|
|
|
@item dividing by zero: |
|
@cindex dividing by zero, floating-point |
|
@cindex floating-point dividing by zero |
|
@cindex floating-point unidentified fault, FP divide-by-zero |
|
@code{-55 throw} (Floating-point unidentified fault) |
|
|
|
@item exponent too big for conversion (@code{DF!}, @code{DF@@}, @code{SF!}, @code{SF@@}): |
|
@cindex exponent too big for conversion (@code{DF!}, @code{DF@@}, @code{SF!}, @code{SF@@}) |
|
System dependent. On IEEE-FP based systems the number is converted into |
|
an infinity. |
|
|
|
@item @var{float}<1 (@code{FACOSH}): |
|
@cindex @code{FACOSH}, @var{float}<1 |
|
@cindex floating-point unidentified fault, @code{FACOSH} |
|
@code{-55 throw} (Floating-point unidentified fault) |
|
|
|
@item @var{float}=<-1 (@code{FLNP1}): |
|
@cindex @code{FLNP1}, @var{float}=<-1 |
|
@cindex floating-point unidentified fault, @code{FLNP1} |
|
@code{-55 throw} (Floating-point unidentified fault). On IEEE-FP systems |
|
negative infinity is typically produced for @var{float}=-1. |
|
|
|
@item @var{float}=<0 (@code{FLN}, @code{FLOG}): |
|
@cindex @code{FLN}, @var{float}=<0 |
|
@cindex @code{FLOG}, @var{float}=<0 |
|
@cindex floating-point unidentified fault, @code{FLN} or @code{FLOG} |
|
@code{-55 throw} (Floating-point unidentified fault). On IEEE-FP systems |
|
negative infinity is typically produced for @var{float}=0. |
|
|
|
@item @var{float}<0 (@code{FASINH}, @code{FSQRT}): |
|
@cindex @code{FASINH}, @var{float}<0 |
|
@cindex @code{FSQRT}, @var{float}<0 |
|
@cindex floating-point unidentified fault, @code{FASINH} or @code{FSQRT} |
|
@code{-55 throw} (Floating-point unidentified fault). @code{fasinh} |
|
produces values for these inputs on my Linux box (Bug in the C library?) |
|
|
|
@item |@var{float}|>1 (@code{FACOS}, @code{FASIN}, @code{FATANH}): |
|
@cindex @code{FACOS}, |@var{float}|>1 |
|
@cindex @code{FASIN}, |@var{float}|>1 |
|
@cindex @code{FATANH}, |@var{float}|>1 |
|
@cindex floating-point unidentified fault, @code{FACOS}, @code{FASIN} or @code{FATANH} |
|
@code{-55 throw} (Floating-point unidentified fault). |
|
|
|
@item integer part of float cannot be represented by @var{d} in @code{F>D}: |
|
@cindex @code{F>D}, integer part of float cannot be represented by @var{d} |
|
@cindex floating-point unidentified fault, @code{F>D} |
|
@code{-55 throw} (Floating-point unidentified fault). |
|
|
|
@item string larger than pictured numeric output area (@code{f.}, @code{fe.}, @code{fs.}): |
|
@cindex string larger than pictured numeric output area (@code{f.}, @code{fe.}, @code{fs.}) |
|
This does not happen. |
|
@end table |
|
|
|
@c ===================================================================== |
|
@node The optional Locals word set, The optional Memory-Allocation word set, The optional Floating-Point word set, ANS conformance |
|
@section The optional Locals word set |
|
@c ===================================================================== |
|
@cindex system documentation, locals words |
|
@cindex locals words, system documentation |
|
|
|
@menu |
|
* locals-idef:: Implementation Defined Options |
|
* locals-ambcond:: Ambiguous Conditions |
|
@end menu |
|
|
|
|
|
@c --------------------------------------------------------------------- |
|
@node locals-idef, locals-ambcond, The optional Locals word set, The optional Locals word set |
|
@subsection Implementation Defined Options |
|
@c --------------------------------------------------------------------- |
|
@cindex implementation-defined options, locals words |
|
@cindex locals words, implementation-defined options |
|
|
|
@table @i |
|
@item maximum number of locals in a definition: |
|
@cindex maximum number of locals in a definition |
|
@cindex locals, maximum number in a definition |
|
@code{s" #locals" environment? drop .}. Currently 15. This is a lower |
|
bound, e.g., on a 32-bit machine there can be 41 locals of up to 8 |
|
characters. The number of locals in a definition is bounded by the size |
|
of locals-buffer, which contains the names of the locals. |
|
|
|
@end table |
|
|
|
|
|
@c --------------------------------------------------------------------- |
|
@node locals-ambcond, , locals-idef, The optional Locals word set |
|
@subsection Ambiguous conditions |
|
@c --------------------------------------------------------------------- |
|
@cindex locals words, ambiguous conditions |
|
@cindex ambiguous conditions, locals words |
|
|
|
@table @i |
|
@item executing a named local in interpretation state: |
|
@cindex local in interpretation state |
|
@cindex Interpreting a compile-only word, for a local |
|
Locals have no interpretation semantics. If you try to perform the |
|
interpretation semantics, you will get a @code{-14 throw} somewhere |
|
(Interpreting a compile-only word). If you perform the compilation |
|
semantics, the locals access will be compiled (irrespective of state). |
|
|
|
@item @var{name} not defined by @code{VALUE} or @code{(LOCAL)} (@code{TO}): |
|
@cindex name not defined by @code{VALUE} or @code{(LOCAL)} used by @code{TO} |
|
@cindex @code{TO} on non-@code{VALUE}s and non-locals |
|
@cindex Invalid name argument, @code{TO} |
|
@code{-32 throw} (Invalid name argument) |
|
|
|
@end table |
|
|
|
|
|
@c ===================================================================== |
|
@node The optional Memory-Allocation word set, The optional Programming-Tools word set, The optional Locals word set, ANS conformance |
|
@section The optional Memory-Allocation word set |
|
@c ===================================================================== |
|
@cindex system documentation, memory-allocation words |
|
@cindex memory-allocation words, system documentation |
|
|
|
@menu |
|
* memory-idef:: Implementation Defined Options |
|
@end menu |
|
|
|
|
|
@c --------------------------------------------------------------------- |
|
@node memory-idef, , The optional Memory-Allocation word set, The optional Memory-Allocation word set |
|
@subsection Implementation Defined Options |
|
@c --------------------------------------------------------------------- |
|
@cindex implementation-defined options, memory-allocation words |
|
@cindex memory-allocation words, implementation-defined options |
|
|
|
@table @i |
|
@item values and meaning of @var{ior}: |
|
@cindex @var{ior} values and meaning |
|
The @var{ior}s returned by the file and memory allocation words are |
|
intended as throw codes. They typically are in the range |
|
-512@minus{}-2047 of OS errors. The mapping from OS error numbers to |
|
@var{ior}s is -512@minus{}@var{errno}. |
|
|
|
@end table |
|
|
|
@c ===================================================================== |
|
@node The optional Programming-Tools word set, The optional Search-Order word set, The optional Memory-Allocation word set, ANS conformance |
|
@section The optional Programming-Tools word set |
|
@c ===================================================================== |
|
@cindex system documentation, programming-tools words |
|
@cindex programming-tools words, system documentation |
|
|
|
@menu |
|
* programming-idef:: Implementation Defined Options |
|
* programming-ambcond:: Ambiguous Conditions |
|
@end menu |
|
|
|
|
|
@c --------------------------------------------------------------------- |
|
@node programming-idef, programming-ambcond, The optional Programming-Tools word set, The optional Programming-Tools word set |
|
@subsection Implementation Defined Options |
|
@c --------------------------------------------------------------------- |
|
@cindex implementation-defined options, programming-tools words |
|
@cindex programming-tools words, implementation-defined options |
|
|
|
@table @i |
|
@item ending sequence for input following @code{;CODE} and @code{CODE}: |
|
@cindex @code{;CODE} ending sequence |
|
@cindex @code{CODE} ending sequence |
|
@code{END-CODE} |
|
|
|
@item manner of processing input following @code{;CODE} and @code{CODE}: |
|
@cindex @code{;CODE}, processing input |
|
@cindex @code{CODE}, processing input |
|
The @code{ASSEMBLER} vocabulary is pushed on the search order stack, and |
|
the input is processed by the text interpreter, (starting) in interpret |
|
state. |
|
|
|
@item search order capability for @code{EDITOR} and @code{ASSEMBLER}: |
|
@cindex @code{ASSEMBLER}, search order capability |
|
The ANS Forth search order word set. |
|
|
|
@item source and format of display by @code{SEE}: |
|
@cindex @code{SEE}, source and format of output |
|
The source for @code{see} is the intermediate code used by the inner |
|
interpreter. The current @code{see} tries to output Forth source code |
|
as well as possible. |
|
|
|
@end table |
|
|
|
@c --------------------------------------------------------------------- |
|
@node programming-ambcond, , programming-idef, The optional Programming-Tools word set |
|
@subsection Ambiguous conditions |
|
@c --------------------------------------------------------------------- |
|
@cindex programming-tools words, ambiguous conditions |
|
@cindex ambiguous conditions, programming-tools words |
|
|
|
@table @i |
|
|
|
@item deleting the compilation wordlist (@code{FORGET}): |
|
@cindex @code{FORGET}, deleting the compilation wordlist |
|
Not implemented (yet). |
|
|
|
@item fewer than @var{u}+1 items on the control flow stack (@code{CS-PICK}, @code{CS-ROLL}): |
|
@cindex @code{CS-PICK}, fewer than @var{u}+1 items on the control flow stack |
|
@cindex @code{CS-ROLL}, fewer than @var{u}+1 items on the control flow stack |
|
@cindex control-flow stack underflow |
|
This typically results in an @code{abort"} with a descriptive error |
|
message (may change into a @code{-22 throw} (Control structure mismatch) |
|
in the future). You may also get a memory access error. If you are |
|
unlucky, this ambiguous condition is not caught. |
|
|
|
@item @var{name} can't be found (@code{FORGET}): |
|
@cindex @code{FORGET}, @var{name} can't be found |
|
Not implemented (yet). |
|
|
|
@item @var{name} not defined via @code{CREATE}: |
|
@cindex @code{;CODE}, @var{name} not defined via @code{CREATE} |
|
@code{;CODE} behaves like @code{DOES>} in this respect, i.e., it changes |
|
the execution semantics of the last defined word no matter how it was |
|
defined. |
|
|
|
@item @code{POSTPONE} applied to @code{[IF]}: |
|
@cindex @code{POSTPONE} applied to @code{[IF]} |
|
@cindex @code{[IF]} and @code{POSTPONE} |
|
After defining @code{: X POSTPONE [IF] ; IMMEDIATE}. @code{X} is |
|
equivalent to @code{[IF]}. |
|
|
|
@item reaching the end of the input source before matching @code{[ELSE]} or @code{[THEN]}: |
|
@cindex @code{[IF]}, end of the input source before matching @code{[ELSE]} or @code{[THEN]} |
|
Continue in the same state of conditional compilation in the next outer |
|
input source. Currently there is no warning to the user about this. |
|
|
|
@item removing a needed definition (@code{FORGET}): |
|
@cindex @code{FORGET}, removing a needed definition |
|
Not implemented (yet). |
|
|
|
@end table |
|
|
|
|
|
@c ===================================================================== |
|
@node The optional Search-Order word set, , The optional Programming-Tools word set, ANS conformance |
|
@section The optional Search-Order word set |
|
@c ===================================================================== |
|
@cindex system documentation, search-order words |
|
@cindex search-order words, system documentation |
|
|
|
@menu |
|
* search-idef:: Implementation Defined Options |
|
* search-ambcond:: Ambiguous Conditions |
|
@end menu |
|
|
|
|
|
@c --------------------------------------------------------------------- |
|
@node search-idef, search-ambcond, The optional Search-Order word set, The optional Search-Order word set |
|
@subsection Implementation Defined Options |
|
@c --------------------------------------------------------------------- |
|
@cindex implementation-defined options, search-order words |
|
@cindex search-order words, implementation-defined options |
|
|
|
@table @i |
|
@item maximum number of word lists in search order: |
|
@cindex maximum number of word lists in search order |
|
@cindex search order, maximum depth |
|
@code{s" wordlists" environment? drop .}. Currently 16. |
|
|
|
@item minimum search order: |
|
@cindex minimum search order |
|
@cindex search order, minimum |
|
@code{root root}. |
|
|
|
@end table |
|
|
|
@c --------------------------------------------------------------------- |
|
@node search-ambcond, , search-idef, The optional Search-Order word set |
|
@subsection Ambiguous conditions |
|
@c --------------------------------------------------------------------- |
|
@cindex search-order words, ambiguous conditions |
|
@cindex ambiguous conditions, search-order words |
|
|
|
@table @i |
|
@item changing the compilation wordlist (during compilation): |
|
@cindex changing the compilation wordlist (during compilation) |
|
@cindex compilation wordlist, change before definition ends |
|
The word is entered into the wordlist that was the compilation wordlist |
|
at the start of the definition. Any changes to the name field (e.g., |
|
@code{immediate}) or the code field (e.g., when executing @code{DOES>}) |
|
are applied to the latest defined word (as reported by @code{last} or |
|
@code{lastxt}), if possible, irrespective of the compilation wordlist. |
|
|
|
@item search order empty (@code{previous}): |
|
@cindex @code{previous}, search order empty |
|
@cindex Vocstack empty, @code{previous} |
|
@code{abort" Vocstack empty"}. |
|
|
|
@item too many word lists in search order (@code{also}): |
|
@cindex @code{also}, too many word lists in search order |
|
@cindex Vocstack full, @code{also} |
|
@code{abort" Vocstack full"}. |
|
|
|
@end table |
|
|
|
@c *************************************************************** |
|
@node Model, Integrating Gforth, ANS conformance, Top |
|
@chapter Model |
|
|
|
This chapter has yet to be written. It will contain information, on |
|
which internal structures you can rely. |
|
|
|
@c *************************************************************** |
|
@node Integrating Gforth, Emacs and Gforth, Model, Top |
|
@chapter Integrating Gforth into C programs |
|
|
|
This is not yet implemented. |
|
|
|
Several people like to use Forth as scripting language for applications |
|
that are otherwise written in C, C++, or some other language. |
|
|
|
The Forth system ATLAST provides facilities for embedding it into |
|
applications; unfortunately it has several disadvantages: most |
|
importantly, it is not based on ANS Forth, and it is apparently dead |
|
(i.e., not developed further and not supported). The facilities |
|
provided by Gforth in this area are inspired by ATLASTs facilities, so |
|
making the switch should not be hard. |
|
|
|
We also tried to design the interface such that it can easily be |
|
implemented by other Forth systems, so that we may one day arrive at a |
|
standardized interface. Such a standard interface would allow you to |
|
replace the Forth system without having to rewrite C code. |
|
|
|
You embed the Gforth interpreter by linking with the library |
|
@code{libgforth.a} (give the compiler the option @code{-lgforth}). All |
|
global symbols in this library that belong to the interface, have the |
|
prefix @code{forth_}. (Global symbols that are used internally have the |
|
prefix @code{gforth_}). |
|
|
|
You can include the declarations of Forth types and the functions and |
|
variables of the interface with @code{#include <forth.h>}. |
|
|
|
Types. |
|
|
|
Variables. |
|
|
|
Data and FP Stack pointer. Area sizes. |
|
|
|
functions. |
|
|
|
forth_init(imagefile) |
|
forth_evaluate(string) exceptions? |
|
forth_goto(address) (or forth_execute(xt)?) |
|
forth_continue() (a corountining mechanism) |
|
|
|
Adding primitives. |
|
|
|
No checking. |
|
|
|
Signals? |
|
|
|
Accessing the Stacks |
|
|
|
@node Emacs and Gforth, Image Files, Integrating Gforth, Top |
|
@chapter Emacs and Gforth |
|
@cindex Emacs and Gforth |
|
|
|
@cindex @file{gforth.el} |
|
@cindex @file{forth.el} |
|
@cindex Rydqvist, Goran |
|
@cindex comment editing commands |
|
@cindex @code{\}, editing with Emacs |
|
@cindex debug tracer editing commands |
|
@cindex @code{~~}, removal with Emacs |
|
@cindex Forth mode in Emacs |
|
Gforth comes with @file{gforth.el}, an improved version of |
|
@file{forth.el} by Goran Rydqvist (included in the TILE package). The |
|
improvements are a better (but still not perfect) handling of |
|
indentation. I have also added comment paragraph filling (@kbd{M-q}), |
|
commenting (@kbd{C-x \}) and uncommenting (@kbd{C-u C-x \}) regions and |
|
removing debugging tracers (@kbd{C-x ~}, @pxref{Debugging}). I left the |
|
stuff I do not use alone, even though some of it only makes sense for |
|
TILE. To get a description of these features, enter Forth mode and type |
|
@kbd{C-h m}. |
|
|
|
@cindex source location of error or debugging output in Emacs |
|
@cindex error output, finding the source location in Emacs |
|
@cindex debugging output, finding the source location in Emacs |
|
In addition, Gforth supports Emacs quite well: The source code locations |
|
given in error messages, debugging output (from @code{~~}) and failed |
|
assertion messages are in the right format for Emacs' compilation mode |
|
(@pxref{Compilation, , Running Compilations under Emacs, emacs, Emacs |
|
Manual}) so the source location corresponding to an error or other |
|
message is only a few keystrokes away (@kbd{C-x `} for the next error, |
|
@kbd{C-c C-c} for the error under the cursor). |
|
|
|
@cindex @file{TAGS} file |
|
@cindex @file{etags.fs} |
|
@cindex viewing the source of a word in Emacs |
|
Also, if you @code{include} @file{etags.fs}, a new @file{TAGS} file |
|
(@pxref{Tags, , Tags Tables, emacs, Emacs Manual}) will be produced that |
|
contains the definitions of all words defined afterwards. You can then |
|
find the source for a word using @kbd{M-.}. Note that emacs can use |
|
several tags files at the same time (e.g., one for the Gforth sources |
|
and one for your program, @pxref{Select Tags Table,,Selecting a Tags |
|
Table,emacs, Emacs Manual}). The TAGS file for the preloaded words is |
|
@file{$(datadir)/gforth/$(VERSION)/TAGS} (e.g., |
|
@file{/usr/local/share/gforth/0.2.0/TAGS}). |
|
|
|
@cindex @file{.emacs} |
|
To get all these benefits, add the following lines to your @file{.emacs} |
|
file: |
|
|
|
@example |
|
(autoload 'forth-mode "gforth.el") |
|
(setq auto-mode-alist (cons '("\\.fs\\'" . forth-mode) auto-mode-alist)) |
|
@end example |
|
|
|
@node Image Files, Engine, Emacs and Gforth, Top |
|
@chapter Image Files |
|
@cindex image files |
|
@cindex @code{.fi} files |
|
@cindex precompiled Forth code |
|
@cindex dictionary in persistent form |
|
@cindex persistent form of dictionary |
|
|
|
An image file is a file containing an image of the Forth dictionary, |
|
i.e., compiled Forth code and data residing in the dictionary. By |
|
convention, we use the extension @code{.fi} for image files. |
|
|
|
@menu |
|
* Image File Background:: Why have image files? |
|
* Non-Relocatable Image Files:: don't always work. |
|
* Data-Relocatable Image Files:: are better. |
|
* Fully Relocatable Image Files:: are hard to create. |
|
* Stack and Dictionary Sizes:: Setting the default sizes for an image. |
|
* Running Image Files:: @code{gforth -i @var{file}} or @var{file}. |
|
* Modifying the Startup Sequence:: and turnkey applications. |
|
@end menu |
|
|
|
@node Image File Background, Non-Relocatable Image Files, Image Files, Image Files |
|
@section Image File Background |
|
@cindex image file background |
|
|
|
Our Forth system consists not only of primitives, but also of |
|
definitions written in Forth. Since the Forth compiler itself belongs |
|
to those definitions, it is not possible to start the system with the |
|
primitives and the Forth source alone. Therefore we provide the Forth |
|
code as an image file in nearly executable form. At the start of the |
|
system a C routine loads the image file into memory, sets up the |
|
memory (stacks etc.) according to information in the image file, and |
|
starts executing Forth code. |
|
|
|
The image file variants represent different compromises between the |
|
goals of making it easy to generate image files and making them |
|
portable. |
|
|
|
@cindex relocation at run-time |
|
Win32Forth 3.4 and Mitch Bradleys @code{cforth} use relocation at |
|
run-time. This avoids many of the complications discussed below (image |
|
files are data relocatable without further ado), but costs performance |
|
(one addition per memory access). |
|
|
|
@cindex relocation at load-time |
|
Our loader performs relocation at image load time. The loader also has |
|
to replace tokens standing for primitive calls with the appropriate |
|
code-field addresses (or code addresses in the case of direct |
|
threading). |
|
|
|
There are three kinds of image files, with different degrees of |
|
relocatability: non-relocatable, data-relocatable, and fully relocatable |
|
image files. |
|
|
|
@cindex image file loader |
|
@cindex relocating loader |
|
@cindex loader for image files |
|
These image file variants have several restrictions in common; they are |
|
caused by the design of the image file loader: |
|
|
|
@itemize @bullet |
|
@item |
|
There is only one segment; in particular, this means, that an image file |
|
cannot represent @code{ALLOCATE}d memory chunks (and pointers to |
|
them). And the contents of the stacks are not represented, either. |
|
|
|
@item |
|
The only kinds of relocation supported are: adding the same offset to |
|
all cells that represent data addresses; and replacing special tokens |
|
with code addresses or with pieces of machine code. |
|
|
|
If any complex computations involving addresses are performed, the |
|
results cannot be represented in the image file. Several applications that |
|
use such computations come to mind: |
|
@itemize @minus |
|
@item |
|
Hashing addresses (or data structures which contain addresses) for table |
|
lookup. If you use Gforth's @code{table}s or @code{wordlist}s for this |
|
purpose, you will have no problem, because the hash tables are |
|
recomputed automatically when the system is started. If you use your own |
|
hash tables, you will have to do something similar. |
|
|
|
@item |
|
There's a cute implementation of doubly-linked lists that uses |
|
@code{XOR}ed addresses. You could represent such lists as singly-linked |
|
in the image file, and restore the doubly-linked representation on |
|
startup.@footnote{In my opinion, though, you should think thrice before |
|
using a doubly-linked list (whatever implementation).} |
|
|
|
@item |
|
The code addresses of run-time routines like @code{docol:} cannot be |
|
represented in the image file (because their tokens would be replaced by |
|
machine code in direct threaded implementations). As a workaround, |
|
compute these addresses at run-time with @code{>code-address} from the |
|
executions tokens of selected words (see the definitions of |
|
@code{docol:} and friends in @file{kernel.fs}). |
|
|
|
@item |
|
On many architectures addresses are represented in machine code in some |
|
shifted or mangled form. You cannot put @code{CODE} words that contain |
|
absolute addresses in this form in a relocatable image file. Workarounds |
|
are representing the address in some relative form (e.g., relative to |
|
the CFA, which is present in some register), or loading the address from |
|
a place where it is stored in a non-mangled form. |
|
@end itemize |
|
@end itemize |
|
|
|
@node Non-Relocatable Image Files, Data-Relocatable Image Files, Image File Background, Image Files |
|
@section Non-Relocatable Image Files |
|
@cindex non-relocatable image files |
|
@cindex image files, non-relocatable |
|
|
|
These files are simple memory dumps of the dictionary. They are specific |
|
to the executable (i.e., @file{gforth} file) they were created |
|
with. What's worse, they are specific to the place on which the |
|
dictionary resided when the image was created. Now, there is no |
|
guarantee that the dictionary will reside at the same place the next |
|
time you start Gforth, so there's no guarantee that a non-relocatable |
|
image will work the next time (Gforth will complain instead of crashing, |
|
though). |
|
|
|
You can create a non-relocatable image file with |
|
|
|
doc-savesystem |
|
|
|
@node Data-Relocatable Image Files, Fully Relocatable Image Files, Non-Relocatable Image Files, Image Files |
|
@section Data-Relocatable Image Files |
|
@cindex data-relocatable image files |
|
@cindex image files, data-relocatable |
|
|
|
@cindex @file{gforth.fi}, relocatability |
|
These files contain relocatable data addresses, but fixed code addresses |
|
(instead of tokens). They are specific to the executable (i.e., |
|
@file{gforth} file) they were created with. E.g., the image |
|
@code{gforth.fi} is a data-relocatable image file. |
|
|
|
@cindex @file{comp-image.fs} |
|
You can create a data-relocatable image file by creating two |
|
non-relocatable image files for different base addresses and processing |
|
them with @file{comp-image.fs}, which generates the relocation |
|
information by comparing the images. |
|
|
|
After loading @file{comp-image.fs}, you can invoke the word |
|
@code{comp-image}, which reads the names of the two input files and the |
|
name of the output file from the input stream. This program also |
|
produces some output on the standard output: It displays the offset |
|
(i.e., the difference between the base addresses of the images); |
|
moreover, for each cell that cannot be represented correctly in the |
|
image files, it displays a line like the following one: |
|
|
|
@example |
|
78DC BFFFFA50 BFFFFA40 |
|
@end example |
|
|
|
This means that at offset $78dc from @code{forthstart}, one input image |
|
contains $bffffa50, and the other contains $bffffa40. Since these cells |
|
cannot be represented correctly in the output image, you should examine |
|
these places in the dictionary and verify that these cells are dead |
|
(i.e., not read before they are written). |
|
|
|
E.g., if you want to create an image @file{asm.fi} that has the file |
|
@file{asm.fs} loaded in addition to the usual stuff, you could do it |
|
like this: |
|
|
|
@example |
|
gforth --clear-dictionary asm.fs "savesystem asm.fi1 bye" |
|
gforth --clear-dictionary --offset-image asm.fs "savesystem asm.fi2 bye" |
|
gforth -m 100000 comp-image.fs -e "comp-image asm.fi1 asm.fi2 asm.fi bye" |
|
@end example |
|
|
|
@cindex --clear-dictionary, creating image files |
|
@cindex --offset-image, creating image files |
|
The flag @code{--clear-dictionary} ensures that the dictionary memory is |
|
cleared at the start (so you won't see @code{comp-image} messages about |
|
spurious differences). The flag @code{--offset-image} loads the image at |
|
a small offset from its normal position, ensuring that the resulting |
|
nonrelocatable images have different bases (otherwise @code{comp-image} |
|
cannot work). |
|
|
|
@node Fully Relocatable Image Files, Stack and Dictionary Sizes, Data-Relocatable Image Files, Image Files |
|
@section Fully Relocatable Image Files |
|
@cindex fully relocatable image files |
|
@cindex image files, fully relocatable |
|
|
|
@cindex @file{kern*.fi}, relocatability |
|
These image files have relocatable data addresses, and tokens for code |
|
addresses. They are still a bit machine dependent with respect to the |
|
size and format (byte order, floating point format) of their data. The |
|
@file{kernlxxx.fi} files are fully relocatable. |
|
|
|
@cindex cross-compiler |
|
@cindex metacompiler |
|
At present a fully relocatable image file can only be produced by |
|
@code{cross}, a batch compiler that accepts a Forth-like programming |
|
language. This @code{cross} language has to be documented |
|
yet. |
|
|
|
@cindex target compiler |
|
@code{cross} not only allows the programmer to create fully relocatable |
|
image files, but also to create image files for machines with different |
|
data sizes and data formats than the one used for generating the image |
|
file. This convenience is bought with restrictions and inconveniences in |
|
programming. E.g., addresses have to be stored in memory with special |
|
words (@code{A!}, @code{A,}, etc.) in order to make the code |
|
relocatable. |
|
|
|
@node Stack and Dictionary Sizes, Running Image Files, Fully Relocatable Image Files, Image Files |
|
@section Stack and Dictionary Sizes |
|
@cindex image file, stack and dictionary sizes |
|
@cindex dictionary size default |
|
@cindex stack size default |
|
|
|
If you invoke Gforth with a command line flag for the size |
|
(@pxref{Invoking Gforth}), the size you specify is stored in the |
|
dictionary. If you save the dictionary with @code{savesystem}, this size |
|
will become the default for the resulting image file. E.g., the |
|
following will create a non-relocatable version of gforth.fi with a 1MB |
|
dictionary: |
|
|
|
@example |
|
gforth -m 1M -e "savesystem gforth1M.fi bye" |
|
@end example |
|
|
|
In other words, if you want to set the default size for the dictionary |
|
and the stacks of an image, just invoke Gforth with the appropriate |
|
options when creating the image. When creating a data-relocatable image, |
|
you have to use the same size options for both @code{savesystem}s. |
|
|
|
@cindex stack size, cache-friendly |
|
Note: For cache-friendly behaviour (i.e., good performance), you should |
|
make the sizes of the stacks modulo, say, 2K, somewhat different. E.g., |
|
the default stack sizes are: data: 16k (mod 2k=0); fp: 15.5k (mod |
|
2k=1.5k); return: 15k(mod 2k=1k); locals: 14.5k (mod 2k=0.5k). |
|
|
|
@node Running Image Files, Modifying the Startup Sequence, Stack and Dictionary Sizes, Image Files |
|
@section Running Image Files |
|
@cindex running image files |
|
@cindex invoking image files |
|
@cindex image file invocation |
|
|
|
@cindex -i, invoke image file |
|
@cindex --image file, invoke image file |
|
You can invoke Gforth with an image file @var{image} instead of the |
|
default @file{gforth.fi} with the @code{-i} flag (@pxref{Invoking Gforth}): |
|
@example |
|
gforth -i @var{image} |
|
@end example |
|
|
|
@cindex executable image file |
|
@cindex image files, executable |
|
If your operating system supports starting scripts with a line of the |
|
form @code{#! ...}, you can make your image file executable, and you'll |
|
just have to type the image file name to start Gforth with this image |
|
file (note that the file extension @code{.fi} is just a convention). |
|
|
|
I.e., in most Unix systems, you just have to make the image file |
|
@var{image} executable with |
|
|
|
@example |
|
chmod +x @var{image} |
|
@end example |
|
|
|
and then you can invoke it by simply typing @var{image} instead of |
|
@code{gforth -i @var{image}}. |
|
|
|
@node Modifying the Startup Sequence, , Running Image Files, Image Files |
|
@section Modifying the Startup Sequence |
|
@cindex startup sequence for image file |
|
@cindex image file initialization sequence |
|
@cindex initialization sequence of image file |
|
|
|
You can add your own initialization to the startup sequence through the |
|
deferred word |
|
|
|
doc-'cold |
|
|
|
@code{'cold} is invoked just before the image-specific command line |
|
processing (by default, loading files and evaluating (@code{-e}) strings |
|
starts. |
|
|
|
A sequence for adding your initialization usually looks like this: |
|
|
|
@example |
|
:noname |
|
Defers 'cold \ do other initialization stuff (e.g., rehashing wordlists) |
|
... \ your stuff |
|
; IS 'cold |
|
@end example |
|
|
|
@cindex turnkey image files |
|
@cindex image files, turnkey applications |
|
You can make a turnkey image by letting @code{'cold} execute a word |
|
(your turnkey application) that never returns; instead, it exits Gforth |
|
via @code{bye} or @code{throw}. |
|
|
|
@c ****************************************************************** |
|
@node Engine, Bugs, Image Files, Top |
|
@chapter Engine |
|
@cindex engine |
|
@cindex virtual machine |
|
|
|
Reading this section is not necessary for programming with Gforth. It |
|
may be helpful for finding your way in the Gforth sources. |
|
|
|
The ideas in this section have also been published in the papers |
|
@cite{ANS fig/GNU/??? Forth} (in German) by Bernd Paysan, presented at |
|
the Forth-Tagung '93 and @cite{A Portable Forth Engine} by M. Anton |
|
Ertl, presented at EuroForth '93; the latter is available at |
|
@*@file{http://www.complang.tuwien.ac.at/papers/ertl93.ps.Z}. |
|
|
|
@menu |
|
* Portability:: |
|
* Threading:: |
|
* Primitives:: |
|
* Performance:: |
|
@end menu |
|
|
|
@node Portability, Threading, Engine, Engine |
|
@section Portability |
|
@cindex engine portability |
|
|
|
One of the main goals of the effort is availability across a wide range |
|
of personal machines. fig-Forth, and, to a lesser extent, F83, achieved |
|
this goal by manually coding the engine in assembly language for several |
|
then-popular processors. This approach is very labor-intensive and the |
|
results are short-lived due to progress in computer architecture. |
|
|
|
@cindex C, using C for the engine |
|
Others have avoided this problem by coding in C, e.g., Mitch Bradley |
|
(cforth), Mikael Patel (TILE) and Dirk Zoller (pfe). This approach is |
|
particularly popular for UNIX-based Forths due to the large variety of |
|
architectures of UNIX machines. Unfortunately an implementation in C |
|
does not mix well with the goals of efficiency and with using |
|
traditional techniques: Indirect or direct threading cannot be expressed |
|
in C, and switch threading, the fastest technique available in C, is |
|
significantly slower. Another problem with C is that it is very |
|
cumbersome to express double integer arithmetic. |
|
|
|
@cindex GNU C for the engine |
|
@cindex long long |
|
Fortunately, there is a portable language that does not have these |
|
limitations: GNU C, the version of C processed by the GNU C compiler |
|
(@pxref{C Extensions, , Extensions to the C Language Family, gcc.info, |
|
GNU C Manual}). Its labels as values feature (@pxref{Labels as Values, , |
|
Labels as Values, gcc.info, GNU C Manual}) makes direct and indirect |
|
threading possible, its @code{long long} type (@pxref{Long Long, , |
|
Double-Word Integers, gcc.info, GNU C Manual}) corresponds to Forth's |
|
double numbers@footnote{Unfortunately, long longs are not implemented |
|
properly on all machines (e.g., on alpha-osf1, long longs are only 64 |
|
bits, the same size as longs (and pointers), but they should be twice as |
|
long according to @ref{Long Long, , Double-Word Integers, gcc.info, GNU |
|
C Manual}). So, we had to implement doubles in C after all. Still, on |
|
most machines we can use long longs and achieve better performance than |
|
with the emulation package.}. GNU C is available for free on all |
|
important (and many unimportant) UNIX machines, VMS, 80386s running |
|
MS-DOS, the Amiga, and the Atari ST, so a Forth written in GNU C can run |
|
on all these machines. |
|
|
|
Writing in a portable language has the reputation of producing code that |
|
is slower than assembly. For our Forth engine we repeatedly looked at |
|
the code produced by the compiler and eliminated most compiler-induced |
|
inefficiencies by appropriate changes in the source code. |
|
|
|
@cindex explicit register declarations |
|
@cindex --enable-force-reg, configuration flag |
|
@cindex -DFORCE_REG |
|
However, register allocation cannot be portably influenced by the |
|
programmer, leading to some inefficiencies on register-starved |
|
machines. We use explicit register declarations (@pxref{Explicit Reg |
|
Vars, , Variables in Specified Registers, gcc.info, GNU C Manual}) to |
|
improve the speed on some machines. They are turned on by using the |
|
configuration flag @code{--enable-force-reg} (@code{gcc} switch |
|
@code{-DFORCE_REG}). Unfortunately, this feature not only depends on the |
|
machine, but also on the compiler version: On some machines some |
|
compiler versions produce incorrect code when certain explicit register |
|
declarations are used. So by default @code{-DFORCE_REG} is not used. |
|
|
|
@node Threading, Primitives, Portability, Engine |
|
@section Threading |
|
@cindex inner interpreter implementation |
|
@cindex threaded code implementation |
|
|
|
@cindex labels as values |
|
GNU C's labels as values extension (available since @code{gcc-2.0}, |
|
@pxref{Labels as Values, , Labels as Values, gcc.info, GNU C Manual}) |
|
makes it possible to take the address of @var{label} by writing |
|
@code{&&@var{label}}. This address can then be used in a statement like |
|
@code{goto *@var{address}}. I.e., @code{goto *&&x} is the same as |
|
@code{goto x}. |
|
|
|
@cindex NEXT, indirect threaded |
|
@cindex indirect threaded inner interpreter |
|
@cindex inner interpreter, indirect threaded |
|
With this feature an indirect threaded NEXT looks like: |
|
@example |
|
cfa = *ip++; |
|
ca = *cfa; |
|
goto *ca; |
|
@end example |
|
@cindex instruction pointer |
|
For those unfamiliar with the names: @code{ip} is the Forth instruction |
|
pointer; the @code{cfa} (code-field address) corresponds to ANS Forths |
|
execution token and points to the code field of the next word to be |
|
executed; The @code{ca} (code address) fetched from there points to some |
|
executable code, e.g., a primitive or the colon definition handler |
|
@code{docol}. |
|
|
|
@cindex NEXT, direct threaded |
|
@cindex direct threaded inner interpreter |
|
@cindex inner interpreter, direct threaded |
|
Direct threading is even simpler: |
|
@example |
|
ca = *ip++; |
|
goto *ca; |
|
@end example |
|
|
|
Of course we have packaged the whole thing neatly in macros called |
|
@code{NEXT} and @code{NEXT1} (the part of NEXT after fetching the cfa). |
|
|
|
@menu |
|
* Scheduling:: |
|
* Direct or Indirect Threaded?:: |
|
* DOES>:: |
|
@end menu |
|
|
|
@node Scheduling, Direct or Indirect Threaded?, Threading, Threading |
|
@subsection Scheduling |
|
@cindex inner interpreter optimization |
|
|
|
There is a little complication: Pipelined and superscalar processors, |
|
i.e., RISC and some modern CISC machines can process independent |
|
instructions while waiting for the results of an instruction. The |
|
compiler usually reorders (schedules) the instructions in a way that |
|
achieves good usage of these delay slots. However, on our first tries |
|
the compiler did not do well on scheduling primitives. E.g., for |
|
@code{+} implemented as |
|
@example |
|
n=sp[0]+sp[1]; |
|
sp++; |
|
sp[0]=n; |
|
NEXT; |
|
@end example |
|
the NEXT comes strictly after the other code, i.e., there is nearly no |
|
scheduling. After a little thought the problem becomes clear: The |
|
compiler cannot know that sp and ip point to different addresses (and |
|
the version of @code{gcc} we used would not know it even if it was |
|
possible), so it could not move the load of the cfa above the store to |
|
the TOS. Indeed the pointers could be the same, if code on or very near |
|
the top of stack were executed. In the interest of speed we chose to |
|
forbid this probably unused ``feature'' and helped the compiler in |
|
scheduling: NEXT is divided into the loading part (@code{NEXT_P1}) and |
|
the goto part (@code{NEXT_P2}). @code{+} now looks like: |
|
@example |
|
n=sp[0]+sp[1]; |
|
sp++; |
|
NEXT_P1; |
|
sp[0]=n; |
|
NEXT_P2; |
|
@end example |
|
This can be scheduled optimally by the compiler. |
|
|
|
This division can be turned off with the switch @code{-DCISC_NEXT}. This |
|
switch is on by default on machines that do not profit from scheduling |
|
(e.g., the 80386), in order to preserve registers. |
|
|
|
@node Direct or Indirect Threaded?, DOES>, Scheduling, Threading |
|
@subsection Direct or Indirect Threaded? |
|
@cindex threading, direct or indirect? |
|
|
|
@cindex -DDIRECT_THREADED |
|
Both! After packaging the nasty details in macro definitions we |
|
realized that we could switch between direct and indirect threading by |
|
simply setting a compilation flag (@code{-DDIRECT_THREADED}) and |
|
defining a few machine-specific macros for the direct-threading case. |
|
On the Forth level we also offer access words that hide the |
|
differences between the threading methods (@pxref{Threading Words}). |
|
|
|
Indirect threading is implemented completely machine-independently. |
|
Direct threading needs routines for creating jumps to the executable |
|
code (e.g. to docol or dodoes). These routines are inherently |
|
machine-dependent, but they do not amount to many source lines. I.e., |
|
even porting direct threading to a new machine is a small effort. |
|
|
|
@cindex --enable-indirect-threaded, configuration flag |
|
@cindex --enable-direct-threaded, configuration flag |
|
The default threading method is machine-dependent. You can enforce a |
|
specific threading method when building Gforth with the configuration |
|
flag @code{--enable-direct-threaded} or |
|
@code{--enable-indirect-threaded}. Note that direct threading is not |
|
supported on all machines. |
|
|
|
@node DOES>, , Direct or Indirect Threaded?, Threading |
|
@subsection DOES> |
|
@cindex @code{DOES>} implementation |
|
|
|
@cindex dodoes routine |
|
@cindex DOES-code |
|
One of the most complex parts of a Forth engine is @code{dodoes}, i.e., |
|
the chunk of code executed by every word defined by a |
|
@code{CREATE}...@code{DOES>} pair. The main problem here is: How to find |
|
the Forth code to be executed, i.e. the code after the |
|
@code{DOES>} (the DOES-code)? There are two solutions: |
|
|
|
In fig-Forth the code field points directly to the dodoes and the |
|
DOES-code address is stored in the cell after the code address (i.e. at |
|
@code{@var{cfa} cell+}). It may seem that this solution is illegal in |
|
the Forth-79 and all later standards, because in fig-Forth this address |
|
lies in the body (which is illegal in these standards). However, by |
|
making the code field larger for all words this solution becomes legal |
|
again. We use this approach for the indirect threaded version and for |
|
direct threading on some machines. Leaving a cell unused in most words |
|
is a bit wasteful, but on the machines we are targeting this is hardly a |
|
problem. The other reason for having a code field size of two cells is |
|
to avoid having different image files for direct and indirect threaded |
|
systems (direct threaded systems require two-cell code fields on many |
|
machines). |
|
|
|
@cindex DOES-handler |
|
The other approach is that the code field points or jumps to the cell |
|
after @code{DOES}. In this variant there is a jump to @code{dodoes} at |
|
this address (the DOES-handler). @code{dodoes} can then get the |
|
DOES-code address by computing the code address, i.e., the address of |
|
the jump to dodoes, and add the length of that jump field. A variant of |
|
this is to have a call to @code{dodoes} after the @code{DOES>}; then the |
|
return address (which can be found in the return register on RISCs) is |
|
the DOES-code address. Since the two cells available in the code field |
|
are used up by the jump to the code address in direct threading on many |
|
architectures, we use this approach for direct threading on these |
|
architectures. We did not want to add another cell to the code field. |
|
|
|
@node Primitives, Performance, Threading, Engine |
|
@section Primitives |
|
@cindex primitives, implementation |
|
@cindex virtual machine instructions, implementation |
|
|
|
@menu |
|
* Automatic Generation:: |
|
* TOS Optimization:: |
|
* Produced code:: |
|
@end menu |
|
|
|
@node Automatic Generation, TOS Optimization, Primitives, Primitives |
|
@subsection Automatic Generation |
|
@cindex primitives, automatic generation |
|
|
|
@cindex @file{prims2x.fs} |
|
Since the primitives are implemented in a portable language, there is no |
|
longer any need to minimize the number of primitives. On the contrary, |
|
having many primitives has an advantage: speed. In order to reduce the |
|
number of errors in primitives and to make programming them easier, we |
|
provide a tool, the primitive generator (@file{prims2x.fs}), that |
|
automatically generates most (and sometimes all) of the C code for a |
|
primitive from the stack effect notation. The source for a primitive |
|
has the following form: |
|
|
|
@cindex primitive source format |
|
@format |
|
@var{Forth-name} @var{stack-effect} @var{category} [@var{pronounc.}] |
|
[@code{""}@var{glossary entry}@code{""}] |
|
@var{C code} |
|
[@code{:} |
|
@var{Forth code}] |
|
@end format |
|
|
|
The items in brackets are optional. The category and glossary fields |
|
are there for generating the documentation, the Forth code is there |
|
for manual implementations on machines without GNU C. E.g., the source |
|
for the primitive @code{+} is: |
|
@example |
|
+ n1 n2 -- n core plus |
|
n = n1+n2; |
|
@end example |
|
|
|
This looks like a specification, but in fact @code{n = n1+n2} is C |
|
code. Our primitive generation tool extracts a lot of information from |
|
the stack effect notations@footnote{We use a one-stack notation, even |
|
though we have separate data and floating-point stacks; The separate |
|
notation can be generated easily from the unified notation.}: The number |
|
of items popped from and pushed on the stack, their type, and by what |
|
name they are referred to in the C code. It then generates a C code |
|
prelude and postlude for each primitive. The final C code for @code{+} |
|
looks like this: |
|
|
|
@example |
|
I_plus: /* + ( n1 n2 -- n ) */ /* label, stack effect */ |
|
/* */ /* documentation */ |
|
@{ |
|
DEF_CA /* definition of variable ca (indirect threading) */ |
|
Cell n1; /* definitions of variables */ |
|
Cell n2; |
|
Cell n; |
|
n1 = (Cell) sp[1]; /* input */ |
|
n2 = (Cell) TOS; |
|
sp += 1; /* stack adjustment */ |
|
NAME("+") /* debugging output (with -DDEBUG) */ |
|
@{ |
|
n = n1+n2; /* C code taken from the source */ |
|
@} |
|
NEXT_P1; /* NEXT part 1 */ |
|
TOS = (Cell)n; /* output */ |
|
NEXT_P2; /* NEXT part 2 */ |
|
@} |
|
@end example |
|
|
|
This looks long and inefficient, but the GNU C compiler optimizes quite |
|
well and produces optimal code for @code{+} on, e.g., the R3000 and the |
|
HP RISC machines: Defining the @code{n}s does not produce any code, and |
|
using them as intermediate storage also adds no cost. |
|
|
|
There are also other optimizations, that are not illustrated by this |
|
example: Assignments between simple variables are usually for free (copy |
|
propagation). If one of the stack items is not used by the primitive |
|
(e.g. in @code{drop}), the compiler eliminates the load from the stack |
|
(dead code elimination). On the other hand, there are some things that |
|
the compiler does not do, therefore they are performed by |
|
@file{prims2x.fs}: The compiler does not optimize code away that stores |
|
a stack item to the place where it just came from (e.g., @code{over}). |
|
|
|
While programming a primitive is usually easy, there are a few cases |
|
where the programmer has to take the actions of the generator into |
|
account, most notably @code{?dup}, but also words that do not (always) |
|
fall through to NEXT. |
|
|
|
@node TOS Optimization, Produced code, Automatic Generation, Primitives |
|
@subsection TOS Optimization |
|
@cindex TOS optimization for primitives |
|
@cindex primitives, keeping the TOS in a register |
|
|
|
An important optimization for stack machine emulators, e.g., Forth |
|
engines, is keeping one or more of the top stack items in |
|
registers. If a word has the stack effect @var{in1}...@var{inx} @code{--} |
|
@var{out1}...@var{outy}, keeping the top @var{n} items in registers |
|
@itemize @bullet |
|
@item |
|
is better than keeping @var{n-1} items, if @var{x>=n} and @var{y>=n}, |
|
due to fewer loads from and stores to the stack. |
|
@item is slower than keeping @var{n-1} items, if @var{x<>y} and @var{x<n} and |
|
@var{y<n}, due to additional moves between registers. |
|
@end itemize |
|
|
|
@cindex -DUSE_TOS |
|
@cindex -DUSE_NO_TOS |
|
In particular, keeping one item in a register is never a disadvantage, |
|
if there are enough registers. Keeping two items in registers is a |
|
disadvantage for frequent words like @code{?branch}, constants, |
|
variables, literals and @code{i}. Therefore our generator only produces |
|
code that keeps zero or one items in registers. The generated C code |
|
covers both cases; the selection between these alternatives is made at |
|
C-compile time using the switch @code{-DUSE_TOS}. @code{TOS} in the C |
|
code for @code{+} is just a simple variable name in the one-item case, |
|
otherwise it is a macro that expands into @code{sp[0]}. Note that the |
|
GNU C compiler tries to keep simple variables like @code{TOS} in |
|
registers, and it usually succeeds, if there are enough registers. |
|
|
|
@cindex -DUSE_FTOS |
|
@cindex -DUSE_NO_FTOS |
|
The primitive generator performs the TOS optimization for the |
|
floating-point stack, too (@code{-DUSE_FTOS}). For floating-point |
|
operations the benefit of this optimization is even larger: |
|
floating-point operations take quite long on most processors, but can be |
|
performed in parallel with other operations as long as their results are |
|
not used. If the FP-TOS is kept in a register, this works. If |
|
it is kept on the stack, i.e., in memory, the store into memory has to |
|
wait for the result of the floating-point operation, lengthening the |
|
execution time of the primitive considerably. |
|
|
|
The TOS optimization makes the automatic generation of primitives a |
|
bit more complicated. Just replacing all occurrences of @code{sp[0]} by |
|
@code{TOS} is not sufficient. There are some special cases to |
|
consider: |
|
@itemize @bullet |
|
@item In the case of @code{dup ( w -- w w )} the generator must not |
|
eliminate the store to the original location of the item on the stack, |
|
if the TOS optimization is turned on. |
|
@item Primitives with stack effects of the form @code{--} |
|
@var{out1}...@var{outy} must store the TOS to the stack at the start. |
|
Likewise, primitives with the stack effect @var{in1}...@var{inx} @code{--} |
|
must load the TOS from the stack at the end. But for the null stack |
|
effect @code{--} no stores or loads should be generated. |
|
@end itemize |
|
|
|
@node Produced code, , TOS Optimization, Primitives |
|
@subsection Produced code |
|
@cindex primitives, assembly code listing |
|
|
|
@cindex @file{engine.s} |
|
To see what assembly code is produced for the primitives on your machine |
|
with your compiler and your flag settings, type @code{make engine.s} and |
|
look at the resulting file @file{engine.s}. |
|
|
|
@node Performance, , Primitives, Engine |
|
@section Performance |
|
@cindex performance of some Forth interpreters |
|
@cindex engine performance |
|
@cindex benchmarking Forth systems |
|
@cindex Gforth performance |
|
|
|
On RISCs the Gforth engine is very close to optimal; i.e., it is usually |
|
impossible to write a significantly faster engine. |
|
|
|
On register-starved machines like the 386 architecture processors |
|
improvements are possible, because @code{gcc} does not utilize the |
|
registers as well as a human, even with explicit register declarations; |
|
e.g., Bernd Beuster wrote a Forth system fragment in assembly language |
|
and hand-tuned it for the 486; this system is 1.19 times faster on the |
|
Sieve benchmark on a 486DX2/66 than Gforth compiled with |
|
@code{gcc-2.6.3} with @code{-DFORCE_REG}. |
|
|
|
@cindex Win32Forth performance |
|
@cindex NT Forth performance |
|
@cindex eforth performance |
|
@cindex ThisForth performance |
|
@cindex PFE performance |
|
@cindex TILE performance |
|
However, this potential advantage of assembly language implementations |
|
is not necessarily realized in complete Forth systems: We compared |
|
Gforth (direct threaded, compiled with @code{gcc-2.6.3} and |
|
@code{-DFORCE_REG}) with Win32Forth 1.2093, LMI's NT Forth (Beta, May |
|
1994) and Eforth (with and without peephole (aka pinhole) optimization |
|
of the threaded code); all these systems were written in assembly |
|
language. We also compared Gforth with three systems written in C: |
|
PFE-0.9.14 (compiled with @code{gcc-2.6.3} with the default |
|
configuration for Linux: @code{-O2 -fomit-frame-pointer -DUSE_REGS |
|
-DUNROLL_NEXT}), ThisForth Beta (compiled with gcc-2.6.3 -O3 |
|
-fomit-frame-pointer; ThisForth employs peephole optimization of the |
|
threaded code) and TILE (compiled with @code{make opt}). We benchmarked |
|
Gforth, PFE, ThisForth and TILE on a 486DX2/66 under Linux. Kenneth |
|
O'Heskin kindly provided the results for Win32Forth and NT Forth on a |
|
486DX2/66 with similar memory performance under Windows NT. Marcel |
|
Hendrix ported Eforth to Linux, then extended it to run the benchmarks, |
|
added the peephole optimizer, ran the benchmarks and reported the |
|
results. |
|
|
|
We used four small benchmarks: the ubiquitous Sieve; bubble-sorting and |
|
matrix multiplication come from the Stanford integer benchmarks and have |
|
been translated into Forth by Martin Fraeman; we used the versions |
|
included in the TILE Forth package, but with bigger data set sizes; and |
|
a recursive Fibonacci number computation for benchmarking calling |
|
performance. The following table shows the time taken for the benchmarks |
|
scaled by the time taken by Gforth (in other words, it shows the speedup |
|
factor that Gforth achieved over the other systems). |
|
|
|
@example |
|
relative Win32- NT eforth This- |
|
time Gforth Forth Forth eforth +opt PFE Forth TILE |
|
sieve 1.00 1.39 1.14 1.39 0.85 1.58 3.18 8.58 |
|
bubble 1.00 1.31 1.41 1.48 0.88 1.50 3.88 |
|
matmul 1.00 1.47 1.35 1.46 0.74 1.58 4.09 |
|
fib 1.00 1.52 1.34 1.22 0.86 1.74 2.99 4.30 |
|
@end example |
|
|
|
You may find the good performance of Gforth compared with the systems |
|
written in assembly language quite surprising. One important reason for |
|
the disappointing performance of these systems is probably that they are |
|
not written optimally for the 486 (e.g., they use the @code{lods} |
|
instruction). In addition, Win32Forth uses a comfortable, but costly |
|
method for relocating the Forth image: like @code{cforth}, it computes |
|
the actual addresses at run time, resulting in two address computations |
|
per NEXT (@pxref{Image File Background}). |
|
|
|
Only Eforth with the peephole optimizer performs comparable to |
|
Gforth. The speedups achieved with peephole optimization of threaded |
|
code are quite remarkable. Adding a peephole optimizer to Gforth should |
|
cause similar speedups. |
|
|
|
The speedup of Gforth over PFE, ThisForth and TILE can be easily |
|
explained with the self-imposed restriction of the latter systems to |
|
standard C, which makes efficient threading impossible (however, the |
|
measured implementation of PFE uses a GNU C extension: @ref{Global Reg |
|
Vars, , Defining Global Register Variables, gcc.info, GNU C Manual}). |
|
Moreover, current C compilers have a hard time optimizing other aspects |
|
of the ThisForth and the TILE source. |
|
|
|
Note that the performance of Gforth on 386 architecture processors |
|
varies widely with the version of @code{gcc} used. E.g., @code{gcc-2.5.8} |
|
failed to allocate any of the virtual machine registers into real |
|
machine registers by itself and would not work correctly with explicit |
|
register declarations, giving a 1.3 times slower engine (on a 486DX2/66 |
|
running the Sieve) than the one measured above. |
|
|
|
Note also that there have been several releases of Win32Forth since the |
|
release presented here, so the results presented here may have little |
|
predictive value for the performance of Win32Forth today. |
|
|
|
@cindex @file{Benchres} |
|
In @cite{Translating Forth to Efficient C} by M. Anton Ertl and Martin |
|
Maierhofer (presented at EuroForth '95), an indirect threaded version of |
|
Gforth is compared with Win32Forth, NT Forth, PFE, and ThisForth; that |
|
version of Gforth is 2\%@minus{}8\% slower on a 486 than the version |
|
used here. The paper available at |
|
@*@file{http://www.complang.tuwien.ac.at/papers/ertl&maierhofer95.ps.gz}; |
|
it also contains numbers for some native code systems. You can find a |
|
newer version of these measurements at |
|
@file{http://www.complang.tuwien.ac.at/forth/performance.html}. You can |
|
find numbers for Gforth on various machines in @file{Benchres}. |
|
|
|
@node Bugs, Origin, Engine, Top |
|
@chapter Bugs |
|
@cindex bug reporting |
|
|
|
Known bugs are described in the file BUGS in the Gforth distribution. |
|
|
|
If you find a bug, please send a bug report to |
|
@code{bug-gforth@@gnu.ai.mit.edu}. A bug report should |
|
describe the Gforth version used (it is announced at the start of an |
|
interactive Gforth session), the machine and operating system (on Unix |
|
systems you can use @code{uname -a} to produce this information), the |
|
installation options (send the @file{config.status} file), and a |
|
complete list of changes you (or your installer) have made to the Gforth |
|
sources (if any); it should contain a program (or a sequence of keyboard |
|
commands) that reproduces the bug and a description of what you think |
|
constitutes the buggy behaviour. |
|
|
|
For a thorough guide on reporting bugs read @ref{Bug Reporting, , How |
|
to Report Bugs, gcc.info, GNU C Manual}. |
|
|
|
|
|
@node Origin, Word Index, Bugs, Top |
|
@chapter Authors and Ancestors of Gforth |
|
|
|
@section Authors and Contributors |
|
@cindex authors of Gforth |
|
@cindex contributors to Gforth |
|
|
|
The Gforth project was started in mid-1992 by Bernd Paysan and Anton |
|
Ertl. The third major author was Jens Wilke. Lennart Benschop (who was |
|
one of Gforth's first users, in mid-1993) and Stuart Ramsden inspired us |
|
with their continuous feedback. Lennart Benshop contributed |
|
@file{glosgen.fs}, while Stuart Ramsden has been working on automatic |
|
support for calling C libraries. Helpful comments also came from Paul |
|
Kleinrubatscher, Christian Pirker, Dirk Zoller, Marcel Hendrix, John |
|
Wavrik, Barrie Stott and Marc de Groot. |
|
|
|
Gforth also owes a lot to the authors of the tools we used (GCC, CVS, |
|
and autoconf, among others), and to the creators of the Internet: Gforth |
|
was developed across the Internet, and its authors have not met |
|
physically yet. |
|
|
|
@section Pedigree |
|
@cindex Pedigree of Gforth |
|
|
|
Gforth descends from BigForth (1993) and fig-Forth. Gforth and PFE (by |
|
Dirk Zoller) will cross-fertilize each other. Of course, a significant |
|
part of the design of Gforth was prescribed by ANS Forth. |
|
|
|
Bernd Paysan wrote BigForth, a descendent from TurboForth, an unreleased |
|
32 bit native code version of VolksForth for the Atari ST, written |
|
mostly by Dietrich Weineck. |
|
|
|
VolksForth descends from F83. It was written by Klaus Schleisiek, Bernd |
|
Pennemann, Georg Rehfeld and Dietrich Weineck for the C64 (called |
|
UltraForth there) in the mid-80s and ported to the Atari ST in 1986. |
|
|
|
Henry Laxen and Mike Perry wrote F83 as a model implementation of the |
|
Forth-83 standard. !! Pedigree? When? |
|
|
|
A team led by Bill Ragsdale implemented fig-Forth on many processors in |
|
1979. Robert Selzer and Bill Ragsdale developed the original |
|
implementation of fig-Forth for the 6502 based on microForth. |
|
|
|
The principal architect of microForth was Dean Sanderson. microForth was |
|
FORTH, Inc.'s first off-the-shelf product. It was developed in 1976 for |
|
the 1802, and subsequently implemented on the 8080, the 6800 and the |
|
Z80. |
|
|
|
All earlier Forth systems were custom-made, usually by Charles Moore, |
|
who discovered (as he puts it) Forth during the late 60s. The first full |
|
Forth existed in 1971. |
|
|
|
A part of the information in this section comes from @cite{The Evolution |
|
of Forth} by Elizabeth D. Rather, Donald R. Colburn and Charles |
|
H. Moore, presented at the HOPL-II conference and preprinted in SIGPLAN |
|
Notices 28(3), 1993. You can find more historical and genealogical |
|
information about Forth there. |
|
|
|
@node Word Index, Concept Index, Origin, Top |
|
@unnumbered Word Index |
|
|
|
This index is as incomplete as the manual. Each word is listed with |
|
stack effect and wordset. |
|
|
|
@printindex fn |
|
|
|
@node Concept Index, , Word Index, Top |
|
@unnumbered Concept and Word Index |
|
|
|
This index is as incomplete as the manual. Not all entries listed are |
|
present verbatim in the text. Only the names are listed for the words |
|
here. |
|
|
|
@printindex cp |
|
|
@contents |
@contents |
@bye |
@bye |