gforth: gforth/Attic/gforth.ds

Diff for /gforth/Attic/gforth.ds between version 1.3 and 1.24

-version 1.3, Wed Nov 23 16:54:39 1994 UTC
+version 1.24, Wed Nov 15 17:29:07 1995 UTC
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  \input texinfo   @c -*-texinfo-*-
  @comment The source is gforth.ds, from which gforth.texi is generated
  @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.)
  @ifinfo
- This file documents GNU Forth 0.0
+ This file documents Gforth 0.1
- Copyright @copyright{} 1994 GNU Forth Development Group
+ Copyright @copyright{} 1995 Free Software Foundation, Inc.
       Permission is granted to make and distribute verbatim copies of
       this manual provided the copyright notice and this permission notice
  Line 36
  Line 36
  Line 36
       of in the original English.
  @end ifinfo
+ @finalout
  @titlepage
  @sp 10
- @center @titlefont{GNU Forth Manual}
+ @center @titlefont{Gforth Manual}
  @sp 2
- @center for version 0.0
+ @center for version 0.1
  @sp 2
  @center Anton Ertl
+ @sp 3
+ @center This manual is under construction
  @comment  The following two commands start the copyright page.
  @page
  @vskip 0pt plus 1filll
- Copyright @copyright{} 1994 GNU Forth Development Group
+ Copyright @copyright{} 1995 Free Software Foundation, Inc.
  @comment !! Published by ... or You can get a copy of this manual ...
- Line 72
+ Line 75
  Line 72
  Line 75
  @node Top, License, (dir), (dir)
  @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 0.1.
  @end ifinfo
  @menu
  * License::
- * Goals::               About the GNU Forth Project
+ * Goals::                       About the Gforth Project
  * Other Books::         Things you might want to read
- * Invocation::          Starting GNU Forth
+ * Invocation::                  Starting Gforth
- * Words::               Forth words available in GNU Forth
+ * Words::                       Forth words available in Gforth
  * ANS conformance::     Implementation-defined options etc.
- * Model::               The abstract machine of GNU Forth
+ * Model::                       The abstract machine of Gforth
- * Emacs and GForth::    The GForth Mode
+ * Emacs and Gforth::            The Gforth Mode
  * Internals::           Implementation details
  * Bugs::                How to report them
- * Pedigree::            Ancestors of GNU Forth
+ * Pedigree::                    Ancestors of Gforth
  * Word Index::          An item for each Forth word
  * Node Index::          An item for each node
  @end menu
  @node License, Goals, Top, Top
- @unnumbered License
+ @unnumbered GNU GENERAL PUBLIC LICENSE
- !! Insert GPL here
+ @center Version 2, June 1991
+ @display
+ Copyright @copyright{} 1989, 1991 Free Software Foundation, Inc.
+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
+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
+ @node    Preface
+ @comment node-name,     next,           previous, up
  @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}
  for introductory material.
  @end iftex
  @node    Goals, Other Books, License, Top
  @comment node-name,     next,           previous, up
- @chapter Goals of GNU Forth
+ @chapter Goals of Gforth
  @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:
  @itemize @bullet
  @item
- GNU Forth should conform to the ANSI Forth standard.
+ Gforth should conform to the ANSI Forth standard.
  @item
  It should be a model, i.e. it should define all the
  implementation-dependent things.
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+ Line 515
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  is the most difficult one.
  @end itemize
- To achieve these goals GNU Forth should be
+ To achieve these goals Gforth should be
  @itemize @bullet
  @item
  Similar to previous models (fig-Forth, F83)
- Line 137
+ Line 531
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  Line 531
  Available on many machines/easy to port.
  @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
- 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
  @chapter Other books on ANS Forth
  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
  deviations of the book.
  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)
+-7179; Fax.: (303) 843-9880) for about $300.
+ @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}.
- @cite{Forth: The new model} by Jack Woehr (!! Publisher) is an
+ @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
  cover the whole standard. It also contains interesting background
  information (Jack Woehr was in the ANS Forth Technical Committe). It is
- Line 173
+ Line 572
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  Line 572
  @chapter Invocation
  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
  gforth [files] [-e forth-code]
- Line 193
+ Line 592
  Line 193
  Line 592
  @table @code
  @item --image-file @var{file}
+ @item -i @var{file}
  Loads the Forth image @var{file} instead of the default
  @file{gforth.fi}.
  @item --path @var{path}
+ @item -p @var{path}
  Uses @var{path} for searching the image file and Forth source code
  files instead of the default in the environment variable
  @code{GFORTHPATH} or the path specified at installation time (typically
- Line 245
+ Line 646
  Line 245
  Line 646
  after processing the command line (instead of entering interactive mode)
  append @code{-e bye} to the command line.
+ 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:
  On startup the system first executes the system initialization file
  (unless the option @code{--no-init-file} is given; note that the system
- Line 253
+ Line 660
  Line 253
  Line 660
  option @code{--no-rc} is given; this file is first searched in @file{.},
  then in @file{~}, then in the normal path (see above).
- @node Words,  , Invocation, Top
+ @node Words, ANS conformance, Invocation, Top
  @chapter Forth Words
  @menu
- Line 262
+ Line 669
  Line 262
  Line 669
  * Stack Manipulation::
  * Memory access::
  * Control Structures::
- * Local Variables::
+ * Locals::
  * Defining Words::
- * Vocabularies::
+ * Wordlists::
  * Files::
  * Blocks::
  * Other I/O::
  * Programming Tools::
+ * Assembler and Code words::
+ * Threading Words::
  @end menu
  @node Notation, Arithmetic, Words, Words
- Line 277
+ Line 686
  Line 277
  Line 686
  The Forth words are described in this section in the glossary notation
  that has become a de-facto standard for Forth texts, i.e.
- @quotation
+ @format
  @var{word}     @var{Stack effect}   @var{wordset}   @var{pronunciation}
+ @end format
  @var{Description}
- @end quotation
  @table @var
  @item word
- The name of the word. BTW, GNU Forth is case insensitive, so you can
+ The name of the word. BTW, Gforth is case insensitive, so you can
- type the words in in lower case.
+ type the words in in lower case (However, @pxref{core-idef}).
  @item Stack effect
  The stack effect is written in the notation @code{@var{before} --
  @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
  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
  notation. Also, return stack effects are not shown in @var{stack
  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 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.
  @item pronunciation
  How the word is pronounced
- Line 308
+ Line 724
  Line 308
  Line 724
  uses the more portable it will be in theory. However, we suspect that
  most ANS Forth systems on personal machines will feature all
  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
  A description of the behaviour of the word.
  @end table
- The name of a stack item corresponds in the following way with its type:
+ The type of a stack item is specified by the character(s) the name
+ starts with:
  @table @code
- @item name starts with
- Type
  @item f
  Bool, i.e. @code{false} or @code{true}.
  @item c
- Line 353
+ Line 772
  Line 353
  Line 772
  Pointer to a name structure
  @end table
- @node Arithmetic,  , Notation, Words
+ @node Arithmetic, Stack Manipulation, Notation, Words
  @section Arithmetic
  Forth arithmetic is not checked, i.e., you will not hear about integer
  overflow on addition or multiplication, you may hear about division by
- Line 363
+ Line 782
  Line 363
  Line 782
  operators. If you perform division with potentially negative operands,
  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
- 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
  doc-+
  doc--
- Line 377
+ Line 805
  Line 377
  Line 805
  doc-min
  doc-max
+ @node Bitwise operations, Mixed precision, Single precision, Arithmetic
  @subsection Bitwise operations
  doc-and
  doc-or
- Line 385
+ Line 814
  Line 385
  Line 814
  doc-2*
  doc-2/
+ @node Mixed precision, Double precision, Bitwise operations, Arithmetic
  @subsection Mixed precision
  doc-m+
  doc-*/
- Line 396
+ Line 826
  Line 396
  Line 826
  doc-fm/mod
  doc-sm/rem
+ @node Double precision, Floating Point, Mixed precision, Arithmetic
  @subsection Double precision
+ 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-dnegate
- Line 404
+ Line 840
  Line 404
  Line 840
  doc-dmin
  doc-dmax
- @node Stack Manipulation,,,
+ @node Floating Point,  , Double precision, Arithmetic
+ @subsection Floating Point
+ 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} ist the same as
+ @code{+1.0e+1}. 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
+, 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).
+ 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.
+ 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 access, Arithmetic, Words
  @section Stack Manipulation
- gforth has a data stack (aka parameter stack) for characters, cells,
+ Gforth has a data stack (aka parameter stack) for characters, cells,
  addresses, and double cells, a floating point stack for floating point
  numbers, a return stack for storing the return addresses of colon
  definitions and other data, and a locals stack for storing local
- Line 417
+ Line 915
  Line 417
  Line 915
  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
  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.
+ Also, a Forth system is allowed to keep the local variables on the
  return stack. This is reasonable, as local variables usually eliminate
  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
  word, forget about return stack manipulations in that word (see the
  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
  doc-drop
  doc-nip
- Line 444
+ Line 954
  Line 444
  Line 954
  doc-2swap
  doc-2rot
+ @node Floating point stack, Return stack, Data stack, Stack Manipulation
  @subsection Floating point stack
  doc-fdrop
  doc-fnip
- Line 453
+ Line 964
  Line 453
  Line 964
  doc-fswap
  doc-frot
+ @node Return stack, Locals stack, Floating point stack, Stack Manipulation
  @subsection Return stack
  doc->r
  doc-r>
- Line 463
+ Line 975
  Line 463
  Line 975
  doc-2r@
  doc-2rdrop
+ @node Locals stack, Stack pointer manipulation, Return stack, Stack Manipulation
  @subsection Locals stack
+ @node Stack pointer manipulation,  , Locals stack, Stack Manipulation
  @subsection Stack pointer manipulation
  doc-sp@
  doc-sp!
- Line 475
+ Line 989
  Line 475
  Line 989
  doc-lp@
  doc-lp!
- @node Memory access
+ @node Memory access, Control Structures, Stack Manipulation, Words
  @section Memory access
+ @menu
+ * Stack-Memory transfers::
+ * Address arithmetic::
+ * Memory block access::
+ @end menu
+ @node Stack-Memory transfers, Address arithmetic, Memory access, Memory access
  @subsection Stack-Memory transfers
  doc-@
- Line 494
+ Line 1015
  Line 494
  Line 1015
  doc-df@
  doc-df!
+ @node Address arithmetic, Memory block access, Stack-Memory transfers, Memory access
  @subsection Address arithmetic
  ANS Forth does not specify the sizes of the data types. Instead, it
- Line 509
+ Line 1031
  Line 509
  Line 1031
  accessed at addresses divisible by 4. Even if a machine allows unaligned
  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
  (more frequent) accesses to it.
- Line 519
+ Line 1041
  Line 519
  Line 1041
  created.
  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.
+ Note that the standard defines a word @code{char}, which has nothing to
+ do with address arithmetic.
  doc-chars
  doc-char+
  doc-cells
- Line 540
+ Line 1065
  Line 540
  Line 1065
  doc-dfloat+
  doc-dfalign
  doc-dfaligned
+ doc-maxalign
+ doc-maxaligned
+ doc-cfalign
+ doc-cfaligned
  doc-address-unit-bits
+ @node Memory block access,  , Address arithmetic, Memory access
  @subsection Memory block access
  doc-move
- Line 555
+ Line 1085
  Line 555
  Line 1085
  doc-fill
  doc-blank
- @node Control Structures
+ @node Control Structures, Locals, Memory access, Words
  @section Control Structures
  Control structures in Forth cannot be used in interpret state, only in
- Line 563
+ Line 1093
  Line 563
  Line 1093
  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
  @example
- Line 581
+ Line 1121
  Line 581
  Line 1121
  ENDIF
  @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
  recommend using @code{ENDIF}, because it is less confusing for people
  who also know other languages (and is not prone to reinforcing negative
- Line 608
+ Line 1148
  Line 608
  Line 1148
  CASE
    @var{n1} OF @var{code1} ENDOF
    @var{n2} OF @var{code2} ENDOF
-   @dots
+   @dots{}
  ENDCASE
  @end example
- Line 617
+ Line 1157
  Line 617
  Line 1157
  the last @code{ENDOF}. It may use @var{n}, which is on top of the stack,
  but must not consume it.
+ @node Simple Loops, Counted Loops, Selection, Control Structures
  @subsection Simple Loops
  @example
- Line 648
+ Line 1189
  Line 648
  Line 1189
  This is an endless loop.
+ @node Counted Loops, Arbitrary control structures, Simple Loops, Control Structures
  @subsection Counted Loops
  The basic counted loop is:
- Line 685
+ Line 1227
  Line 685
  Line 1227
  @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. These words can be implemented easily on
+ standard systems, so using them does not make your programs hard to
+ port; e.g.:
+ @example
+ : +DO ( compile-time: -- do-sys; run-time: n1 n2 -- )
+     POSTPONE over POSTPONE min POSTPONE ?DO ; immediate
+ @end example
  @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
  between @var{limit-1} and @var{limit} is crossed. E.g.:
- @code{4 0 ?DO  i .  2 +LOOP}   prints @code{0 2}
+ @code{4 0 +DO  i .  2 +LOOP}   prints @code{0 2}
- @code{4 1 ?DO  i .  2 +LOOP}   prints @code{1 3}
+ @code{4 1 +DO  i .  2 +LOOP}   prints @code{1 3}
  The behaviour of @code{@var{n} +LOOP} is peculiar when @var{n} is negative:
- Line 699
+ Line 1255
  Line 699
  Line 1255
  @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.:
- @code{-2 0 ?DO  i .  -1 +LOOP}  prints @code{0 -1}
+ @code{-2 0 -DO  i .  1 -LOOP}  prints @code{0 -1}
- @code{-1 0 ?DO  i .  -1 +LOOP}  prints @code{0}
+ @code{-1 0 -DO  i .  1 -LOOP}  prints @code{0}
- @code{ 0 0 ?DO  i .  -1 +LOOP}  prints nothing
+ @code{ 0 0 -DO  i .  1 -LOOP}  prints nothing
+ Another alternative is @code{@var{n} S+LOOP}, where the negative
+ case behaves symmetrical to the positive case:
+ @code{-2 0 -DO  i .  -1 S+LOOP}  prints @code{0 -1}
- The loop is terminated when the border between @var{limit@minus{}sgn(n)} and
+ The loop is terminated when the border between @var{limit@minus{}sgn(n)}
- @var{limit} is crossed. However, @code{S+LOOP} is not part of the ANS
+ and @var{limit} is crossed. Unfortunately, neither @code{-LOOP} nor
- Forth standard.
+ @code{S+LOOP} are part of the ANS Forth standard, and they are not easy
+ to implement using standard words. If you want to write standard
- @code{?DO} can be replaced by @code{DO}. @code{DO} enters the loop even
+ programs, just avoid counting down.
- when the start and the limit value are equal. We do not recommend using
- @code{DO}. It will just give you maintenance troubles.
+ @code{?DO} can also be replaced by @code{DO}. @code{DO} always enters
+ the loop, independent of the loop parameters. Do not use @code{DO}, even
+ 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{EXIT}. @code{UNLOOP} removes the loop control parameters from the
- Line 729
+ Line 1296
  Line 729
  Line 1296
  NEXT
  @end example
  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}
  and ending with 0. Other Forth systems may behave differently, even if
  they support @code{FOR} loops.
+ @node Arbitrary control structures, Calls and returns, Counted Loops, Control Structures
  @subsection Arbitrary control structures
  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.
+ stack, and this is what we have done in Gforth.
  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
- Line 755
+ Line 1323
  Line 755
  Line 1323
  doc-cs-pick
  doc-cs-roll
- On many systems control-flow stack items take one word, in gforth they
+ 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
- Line 770
+ Line 1338
  Line 770
  Line 1338
  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-s+loop
  doc-+loop
+ doc--loop
  doc-next
  doc-leave
  doc-?leave
  doc-unloop
- doc-undo
+ 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{UNDO}).
+ resolved (by using one of the loop-ending words or @code{DONE}).
  Another group of control structure words are
- Line 841
+ Line 1414
  Line 841
  Line 1414
  @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
  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
+ definition. When the end of the definition is reached, it returns. An
+ earlier return can be forced using
  doc-exit
- Line 854
+ Line 1429
  Line 854
  Line 1429
  doc-;s
+ @node Exception Handling,  , Calls and returns, Control Structures
  @subsection Exception Handling
  doc-catch
  doc-throw
- @node Locals
+ @node Locals, Defining Words, Control Structures, Words
  @section Locals
  Local variables can make Forth programming more enjoyable and Forth
- Line 868
+ Line 1444
  Line 868
  Line 1444
  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
- @subsection gforth locals
+ @node Gforth locals, ANS Forth locals, Locals, Locals
+ @subsection Gforth locals
  Locals can be defined with
- Line 914
+ Line 1498
  Line 914
  Line 1498
   Ar Bi f* Ai Br f* f+ ;
  @end example
- GNU Forth currently supports cells (@code{W:}, @code{W^}), doubles
+ 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
- Line 934
+ Line 1518
  Line 934
  Line 1518
  Currently there is no way to define locals with user-defined data
  structures, but we are working on it.
- GNU Forth allows defining locals everywhere in a colon definition. This poses the following questions:
+ 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?
  Basically, the answer is that locals are visible where you would expect
- Line 994
+ Line 1587
  Line 994
  Line 1587
  BEGIN
    x
  [ 1 CS-ROLL ] THEN
-   { x }
+   @{ x @}
    ...
  UNTIL
  @end example
- Line 1026
+ Line 1619
  Line 1026
  Line 1619
  warns the user if it was too optimisitic:
  @example
  IF
-   { x }
+   @{ x @}
  BEGIN
    \ x ?
  [ 1 cs-roll ] THEN
- Line 1042
+ Line 1635
  Line 1042
  Line 1635
  @example
  IF
    SCOPE
-   { x }
+   @{ x @}
    ENDSCOPE
  BEGIN
  [ 1 cs-roll ] THEN
- Line 1057
+ Line 1650
  Line 1057
  Line 1650
  @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 useer can use
+ 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 item was created.
+ visible at the BEGIN as at the point where the top control-flow stack
+ item was created.
  doc-assume-live
  E.g.,
  @example
- { x }
+ @{ x @}
  AHEAD
  ASSUME-LIVE
  BEGIN
- Line 1086
+ Line 1680
  Line 1086
  Line 1680
  arranged into:
  @example
  BEGIN
-   { x }
+   @{ 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?
  The right answer for the lifetime question would be: A local lives at
- Line 1106
+ Line 1701
  Line 1106
  Line 1701
  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
  The freedom to define locals anywhere has the potential to change
- Line 1117
+ Line 1713
  Line 1117
  Line 1713
  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
+ unlikely to become a conscious programming objective. Still, the number
- number of stack manipulations will be reduced dramatically if local
+ of stack manipulations will be reduced dramatically if local variables
- variables are used liberally (e.g., compare @code{max} in \sect{misc}
+ are used liberally (e.g., compare @code{max} in @ref{Gforth locals} with
- with a traditional implementation of @code{max}).
+ 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
- Line 1174
+ Line 1770
  Line 1174
  Line 1770
  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
- GNU Forth uses an extra locals stack. The most compelling reason for
+ 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
- Line 1197
+ Line 1794
  Line 1197
  Line 1794
  compile the right specialized version, or the general version, as
  appropriate:
- doc-compile-@@local
+ doc-compile-@local
- doc-compile-f@@local
+ doc-compile-f@local
  doc-compile-lp+!
  Combinations of conditional branches and @code{lp+!#} like
- Line 1211
+ Line 1808
  Line 1211
  Line 1808
  initializing code. @code{W:} etc.@ are normal defining words. This
  special area is cleared at the start of every colon definition.
- A special feature of GNU Forths dictionary is used to implement the
+ 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. (@xref{dictionary}). For the present purpose we defined a wordlist
+ 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.,
- Line 1251
+ Line 1848
  Line 1251
  Line 1848
  @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 {\em orig} point to the level after the @code{THEN}. 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
- Line 1301
+ Line 1898
  Line 1301
  Line 1898
  usually less than reclaiming this space would cost in code size.
+ @node ANS Forth locals,  , Gforth locals, Locals
  @subsection ANS Forth locals
  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
+ possible syntaxes is a subset of the syntax we used in the Gforth locals
  wordset, i.e.:
  @example
- Line 1321
+ Line 1919
  Line 1321
  Line 1919
  @itemize @bullet
  @item
- Locals can only be cell-sized values (no type specifers are allowed).
+ 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 we all right. The
+ 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
- Line 1335
+ Line 1933
  Line 1335
  Line 1933
  @end itemize
  Locals defined in this way behave like @code{VALUE}s
- (@xref{values}). I.e., they are initialized from the stack. Using their
+ (@xref{Values}). 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
+ 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{anslocal.fs} to implement the syntax
  on the other system.
- Line 1353
+ Line 1951
  Line 1353
  Line 1951
  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
+ 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 Internals
+ @node Defining Words, Wordlists, Locals, Words
+ @section Defining Words
+ @menu
+ * Values::
+ @end menu
+ @node Values,  , Defining Words, Defining Words
+ @subsection Values
+ @node Wordlists, Files, Defining 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
+ @menu
+ * Debugging::                   Simple and quick.
+ * Assertions::                  Making your programs self-checking.
+ @end menu
+ @node Debugging, Assertions, Programming Tools, Programming Tools
+ @subsection 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-compilig 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
+ 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
+ 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 gcc version and options used.
+ The words 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}.
+ 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}, defining words (for fast
+ defined words) probably 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
+ 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 inclomplete. It is also pretty low-level;
+ some day it will hopefully be made unnecessary by an internals words set
+ 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:
+ Currently there is no installation-independent way for recogizing words
+ defined by a @code{CREATE}...@code{DOES>} word; however, once you know
+ that a word is defined by a @code{CREATE}...@code{DOES>} word, you can
+ use @code{>DOES-CODE}.
+ @node ANS conformance, Model, Words, Top
+ @chapter ANS conformance
+ To the best of our knowledge, Gforth is an
+ ANS Forth System
+ @itemize
+ @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
+ 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 =====================================================================
+ @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 ---------------------------------------------------------------------
+ @table @i
+ @item (Cell) 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
+). Unaligned accesses usually result in a @code{-23 THROW}.
+ @item @code{EMIT} and non-graphic characters:
+ The character is output using the C library function (actually, macro)
+ @code{putchar}.
+ @item character editing of @code{ACCEPT} and @code{EXPECT}:
+ 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:
+ The character set of your computer and display device. Gforth is
+-bit-clean (but some other component in your system may make trouble).
+ @item 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:
+ Any character except the ASCII NUL charcter can be used in a
+ name. Matching is case-insensitive. 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:
+ 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:
+ 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
+ The characters @code{[\]^_'} are the digits with the decimal value
+@minus{}41. There is no way to input many of the larger digits.
+ @item display after input terminates in @code{ACCEPT} and @code{EXPECT}:
+ 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"}:
+ The error string is stored into the variable @code{"error} and a
+ @code{-2 throw} is performed.
+ @item input line terminator:
+ For interactive input, @kbd{C-m} and @kbd{C-j} 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:
+ @code{s" /counted-string" environment? drop .}. Currently 255 characters
+ on all ports, but this may change.
+ @item maximum size of a parsed string:
+ Given by the constant @code{/line}. Currently 255 characters.
+ @item maximum size of a definition name, in characters:
+ @item maximum string length for @code{ENVIRONMENT?}, in characters:
+ @item method of selecting the user input device:
+ 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:
+ The user output device is the standard output. It cannot be redirected
+ from within Gforth, but typically from the command line that starts
+ Gforth. 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:
+ @code{s" address-units-bits" environment? drop .}. 8 in all current
+ ports.
+ @item number representation and arithmetic:
+ Processor-dependent. Binary two's complement on all current ports.
+ @item ranges for integer types:
+ 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:
+ The whole Forth data space is writable.
+ @item size of buffer at @code{WORD}:
+ @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:
+ @code{1 cells .}.
+ @item size of one character in address units:
+ @code{1 chars .}. 1 on all current ports.
+ @item size of the keyboard terminal buffer:
+ 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:
+ @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}:
+ The remainder of dictionary space. You can even use the unused part of
+ the data stack space. The current size can be computed with @code{sp@
+ pad - .}.
+ @item system case-sensitivity characteristics:
+ Dictionary searches are case insensitive. 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:
+ @code{ ok} in interpret state, @code{ compiled} in compile state.
+ @item division rounding:
+ installation dependent. @code{s" floored" environment? drop .}. We leave
+ the choice to 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:
+ -1.
+ @item values returned after arithmetic overflow:
+ On two's complement machines, arithmetic is performed modulo
+**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.
+ @item whether the current definition can be found after @t{DOES>}:
+ No.
+ @end table
+ @c ---------------------------------------------------------------------
+ @node core-ambcond, core-other, core-idef, The Core Words
+ @subsection Ambiguous conditions
+ @c ---------------------------------------------------------------------
+ @table @i
+ @item a name is neither a word nor a number:
+ @code{-13 throw} (Undefined word)
+ @item a definition name exceeds the maximum length allowed:
+ @code{-19 throw} (Word name too long)
+ @item addressing a region not inside the various data spaces of the forth system:
+ 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:
+ 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:
+ You get an execution token representing the compilation semantics
+ instead.
+ @item dividing 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:
+ Not checked. This typically results in mysterious illegal memory
+ accesses, producing @code{-9 throw} (Invalid memory address) or
+ @code{-23 throw} (Address alignment exception).
+ @item insufficient space for loop control parameters:
+ like other return stack overflows.
+ @item insufficient space in the dictionary:
+ Not checked. Similar results as stack overflows. However, typically the
+ error appears at a different place when one inserts or removes code.
+ @item interpreting a word with undefined interpretation semantics:
+ For some words, we defined interpretation semantics. For the others:
+ @code{-14 throw} (Interpreting a compile-only word). Note that this is
+ checked only by the outer (aka text) interpreter; if the word is
+ @code{execute}d in some other way, it will typically perform it's
+ compilation semantics even in interpret state. (We could change @code{'}
+ and relatives not to give the xt of such words, but we think that would
+ be too restrictive).
+ @item 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:
+ Not checked.
+ @item parsed string overflow:
+ @code{PARSE} cannot overflow. @code{WORD} does not check for overflow.
+ @item producing a result out of range:
+ On two's complement machines, arithmetic is performed modulo
+**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:
+ 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, the stacks are not checked and
+ underflows can result in similar behaviour as overflows (of adjacent
+ stacks).
+ @item unexepected end of the input buffer, resulting in an attempt to use a 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:
+ The next invocation of a parsing word returns a string wih length 0.
+ @item @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}:
+ !!???If the argument input source is a valid input source then it gets
+ restored. Otherwise causes @code{-12 THROW}, which, unless caught, issues
+ the message "argument type mismatch" and aborts.
+ @item data space containing definitions gets de-allocated:
+ Deallocation with @code{allot} is not checked. This typically resuls in
+ memory access faults or execution of illegal instructions.
+ @item data space read/write with incorrect alignment:
+ 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,}:
+ Like other alignment errors.
+ @item less than u+2 stack items (@code{PICK} and @code{ROLL}):
+ Not checked. May cause an illegal memory access.
+ @item 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}):
+ @code{abort" last word was headerless"}.
+ @item name not defined by @code{VALUE} used by @code{TO}:
+ @code{-32 throw} (Invalid name argument)
+ @item name not found (@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}):
+ 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}:
+ Assume @code{: X POSTPONE TO ; IMMEDIATE}. @code{X} is equivalent to
+ @code{TO}.
+ @item String longer than a counted string returned by @code{WORD}:
+ 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}):
+ Processor-dependent. Typical behaviours are returning 0 and using only
+ the low bits of the shift count.
+ @item word not defined via @code{CREATE}:
+ @code{>BODY} produces the PFA of the word no matter how it was defined.
+ @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 ---------------------------------------------------------------------
+ @table @i
+ @item nonstandard words using @code{PAD}:
+ None.
+ @item operator's terminal facilities available:
+ !!??
+ @item program data space available:
+ @code{sp@ here - .} gives the space remaining for dictionary and data
+ stack together.
+ @item return stack space available:
+ !!??
+ @item stack space available:
+ @code{sp@ here - .} gives the space remaining for dictionary and data
+ stack together.
+ @item system dictionary space required, in address units:
+ Type @code{here forthstart - .} after startup. At the time of this
+ writing, this gives 70108 (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 =====================================================================
+ @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 ---------------------------------------------------------------------
+ @table @i
+ @item the format for display by @code{LIST}:
+ 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{\}:
+characters.
+ @end table
+ @c ---------------------------------------------------------------------
+ @node block-ambcond, block-other, block-idef, The optional Block word set
+ @subsection Ambiguous conditions
+ @c ---------------------------------------------------------------------
+ @table @i
+ @item correct block read was 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:
+ Typically results in a @code{throw} of some OS-derived value (between
+ -512 and -2048).
+ @item invalid block number:
+ @code{-35 throw} (Invalid block number)
+ @item a program directly alters the contents of @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}:
+ @code{UPDATE} has no effect.
+ @end table
+ @c ---------------------------------------------------------------------
+ @node block-other,  , block-ambcond, The optional Block word set
+ @subsection Other system documentation
+ @c ---------------------------------------------------------------------
+ @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 =====================================================================
+ @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 ---------------------------------------------------------------------
+ @table @i
+ @item @var{d} outside of range of @var{n} in @code{D>S}:
+ 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 =====================================================================
+ @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 ---------------------------------------------------------------------
+ @table @i
+ @item @code{THROW}-codes used in the system:
+ The codes -256@minus{}-511 are used for reporting signals (see
+ @file{errore.fs}). The codes -512@minus{}-2047 are used for OS errors
+ (for file and memory allocation operations). The mapping from OS error
+ numbers to throw code is -512@minus{}@var{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
+} 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 =====================================================================
+ @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 ---------------------------------------------------------------------
+ @table @i
+ @item encoding of keyboard events (@code{EKEY}):
+ Not yet implemeted.
+ @item duration of a system clock tick
+ 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}:
+ 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 ---------------------------------------------------------------------
+ @table @i
+ @item @code{AT-XY} can't be performed on user output device:
+ Largely terminal dependant. 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 =====================================================================
+ @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 ---------------------------------------------------------------------
+ @table @i
+ @item 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 (both with @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:
+ The file words do not raise exceptions (except, perhaps, memory access
+ faults when you pass illegal addresses or file-ids).
+ @item 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
+ System dependent. Gforth just uses the file name format of your OS.
+ @item information returned by @code{FILE-STATUS}:
+ @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 retured mode.
+ @item input file state after an exception when including source:
+ All files that are left via the exception are closed.
+ @item @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:
+ 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:
+ @code{/line}. Currently 255.
+ @item methods of mapping block ranges to files:
+ Currently, the block words automatically access the file
+ @file{blocks.fb} in the currend working directory. More sophisticated
+ methods could be implemented if there is demand (and a volunteer).
+ @item number of string buffers provided by @code{S"}:
+ @item size of string buffer used by @code{S"}:
+ @code{/line}. currently 255.
+ @end table
+ @c ---------------------------------------------------------------------
+ @node file-ambcond,  , file-idef, The optional File-Access word set
+ @subsection Ambiguous conditions
+ @c ---------------------------------------------------------------------
+ @table @i
+ @item attempting to position a file outside it'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:
+ End-of-file, i.e., zero characters are read and no error is reported.
+ @item @var{file-id} is invalid (@code{INCLUDE-FILE}):
+ 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}):
+ The @var{ior} produced by the operation, that discovered the problem, is
+ thrown.
+ @item named file cannot be opened (@code{included}):
+ The @var{ior} produced by @code{open-file} is thrown.
+ @item requesting an unmapped block number:
+ 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:
+ @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 =====================================================================
+ @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 ---------------------------------------------------------------------
+ @table @i
+ @item format and range of floating point numbers:
+ System-dependent; the @code{double} type of C.
+ @item results of @code{REPRESENT} 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:
+ What's the question?!!
+ @item size of floating-point stack:
+ @code{s" FLOATING-STACK" environment? drop .}. Can be changed at startup
+ with the command-line option @code{-f}.
+ @item width of floating-point stack:
+ @code{1 floats}.
+ @end table
+ @c ---------------------------------------------------------------------
+ @node floating-ambcond,  , floating-idef, The optional Floating-Point word set
+ @subsection Ambiguous conditions
+ @c ---------------------------------------------------------------------
+ @table @i
+ @item @code{df@@} or @code{df!} used with an address that is not double-float  aligned:
+ System-dependent. Typically results in an alignment fault like other
+ alignment violations.
+ @item @code{f@@} or @code{f!} used with an address that is not float  aligned:
+ System-dependent. Typically results in an alignment fault like other
+ alignment violations.
+ @item 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:
+ System-dependent. Typically results in an alignment fault like other
+ alignment violations.
+ @item 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}):
+ System-dependent. @code{FATAN2} is implemented using the C library
+ function @code{atan2()}.
+ @item Using 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}:
+ The result is rounded to the nearest float.
+ @item dividing by zero:
+ @code{-55 throw} (Floating-point unidentified fault)
+ @item 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}):
+ @code{-55 throw} (Floating-point unidentified fault)
+ @item @var{float}=<-1 (@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}):
+ @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}):
+ @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}):
+ @code{-55 throw} (Floating-point unidentified fault).
+ @item integer part of float cannot be represented by @var{d} in @code{f>d}:
+ @code{-55 throw} (Floating-point unidentified fault).
+ @item 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 =====================================================================
+ @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 ---------------------------------------------------------------------
+ @table @i
+ @item maximum number of locals 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 ---------------------------------------------------------------------
+ @table @i
+ @item executing a named local in interpretation state:
+ @code{-14 throw} (Interpreting a compile-only word).
+ @item @var{name} not defined by @code{VALUE} or @code{(LOCAL)} (@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 =====================================================================
+ @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 ---------------------------------------------------------------------
+ @table @i
+ @item values and meaning of @var{ior}:
+ 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 =====================================================================
+ @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 ---------------------------------------------------------------------
+ @table @i
+ @item ending sequence for input following @code{;code} and @code{code}:
+ Not implemented (yet).
+ @item manner of processing input following @code{;code} and @code{code}:
+ Not implemented (yet).
+ @item search order capability for @code{EDITOR} and @code{ASSEMBLER}:
+ Not implemented (yet). If they were implemented, they would use the
+ search order wordset.
+ @item source and format of display by @code{SEE}:
+ 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 ---------------------------------------------------------------------
+ @table @i
+ @item deleting the compilation wordlist (@code{FORGET}):
+ Not implemented (yet).
+ @item fewer than @var{u}+1 items on the control flow stack (@code{CS-PICK}, @code{CS-ROLL}):
+ 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}):
+ Not implemented (yet).
+ @item @var{name} not defined via @code{CREATE}:
+ @code{;code} is not implemented (yet). If it were, it would behave like
+ @code{DOES>} in this respect, i.e., change the execution semantics of
+ the last defined word no matter how it was defined.
+ @item @code{POSTPONE} applied to @code{[IF]}:
+ 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]}:
+ 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}):
+ 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 =====================================================================
+ @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 ---------------------------------------------------------------------
+ @table @i
+ @item maximum number of word lists in search order:
+ @code{s" wordlists" environment? drop .}. Currently 16.
+ @item minimum search order:
+ @code{root root}.
+ @end table
+ @c ---------------------------------------------------------------------
+ @node search-ambcond,  , search-idef, The optional Search-Order word set
+ @subsection Ambiguous conditions
+ @c ---------------------------------------------------------------------
+ @table @i
+ @item changing the compilation wordlist (during compilation):
+ The definition is put into the wordlist that is the compilation wordlist
+ when @code{REVEAL} is executed (by @code{;}, @code{DOES>},
+ @code{RECURSIVE}, etc.).
+ @item search order empty (@code{previous}):
+ @code{abort" Vocstack empty"}.
+ @item too many word lists in search order (@code{also}):
+ @code{abort" Vocstack full"}.
+ @end table
+ @node Model, Emacs and Gforth, ANS conformance, Top
+ @chapter Model
+ @node Emacs and Gforth, Internals, Model, Top
+ @chapter Emacs and Gforth
+ Gforth comes with @file{gforth.el}, an improved version of
+ @file{forth.el} by Goran Rydqvist (icluded 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}.
+ 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).
+ 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).
+ 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 Internals, Bugs, Emacs and Gforth, Top
  @chapter Internals
- Reading this section is not necessary for programming with gforth. It
+ Reading this section is not necessary for programming with Gforth. It
- should be helpful for finding your way in the gforth sources.
+ should 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::
+ * System Architecture::
+ * Performance::
+ @end menu
+ @node Portability, Threading, Internals, Internals
  @section Portability
  One of the main goals of the effort is availability across a wide range
- Line 1394
+ Line 3258
  Line 1394
  Line 3258
  double numbers. 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@footnote{Due to Apple's look-and-feel lawsuit it is not
+ machines.
- available on the Mac (@pxref{Boycott, , Protect Your Freedom--Fight
- ``Look And Feel'', gcc.info, GNU C Manual}).}.
  Writing in a portable language has the reputation of producing code that
  is slower than assembly. For our Forth engine we repeatedly looked at
- Line 1414
+ Line 3276
  Line 1414
  Line 3276
  explicit register declarations are used. So by default
  @code{-DFORCE_REG} is not used.
+ @node Threading, Primitives, Portability, Internals
  @section Threading
  GNU C's labels as values extension (available since @code{gcc-2.0},
- Line 1445
+ Line 3308
  Line 1445
  Line 3308
  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
  There is a little complication: Pipelined and superscalar processors,
- Line 1463
+ Line 3333
  Line 1463
  Line 3333
  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 could),
+ the version of @code{gcc} we used would not know it even if it was
- so it could not move the load of the cfa above the store to the
+ possible), so it could not move the load of the cfa above the store to
- TOS. Indeed the pointers could be the same, if code on or very near the
+ the TOS. Indeed the pointers could be the same, if code on or very near
- top of stack were executed. In the interest of speed we chose to forbid
+ the top of stack were executed. In the interest of speed we chose to
- this probably unused ``feature'' and helped the compiler in scheduling:
+ forbid this probably unused ``feature'' and helped the compiler in
- NEXT is divided into the loading part (@code{NEXT_P1}) and the goto part
+ scheduling: NEXT is divided into the loading part (@code{NEXT_P1}) and
- (@code{NEXT_P2}). @code{+} now looks like:
+ the goto part (@code{NEXT_P2}). @code{+} now looks like:
  @example
  n=sp[0]+sp[1];
  sp++;
- Line 1477
+ Line 3347
  Line 1477
  Line 3347
  sp[0]=n;
  NEXT_P2;
  @end example
- This can be scheduled optimally by the compiler (see \sect{TOS}).
+ 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?
  Both! After packaging the nasty details in macro definitions we
- Line 1499
+ Line 3370
  Line 1499
  Line 3370
  lines. I.e., even porting direct threading to a new machine is a small
  effort.
+ @node DOES>,  , Direct or Indirect Threaded?, Threading
  @subsection DOES>
  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
- Line 1516
+ Line 3388
  Line 1516
  Line 3388
  a cell unused in most words is a bit wasteful, but on the machines we
  are targetting 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 (@pxref{image-format}).
+ for direct and indirect threaded systems (@pxref{System Architecture}).
  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
- Line 1530
+ Line 3402
  Line 1530
  Line 3402
  this approach for direct threading. We did not want to add another
  cell to the code field.
+ @node Primitives, System Architecture, Threading, Internals
  @section Primitives
+ @menu
+ * Automatic Generation::
+ * TOS Optimization::
+ * Produced code::
+ @end menu
+ @node Automatic Generation, TOS Optimization, Primitives, Primitives
  @subsection Automatic Generation
  Since the primitives are implemented in a portable language, there is no
- Line 1573
+ Line 3453
  Line 1573
  Line 3453
  @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;
- Line 1582
+ Line 3462
  Line 1582
  Line 3462
  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
- Line 1610
+ Line 3490
  Line 1610
  Line 3490
  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
  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{--}
+ 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
+ @var{out1}...@var{outy}, keeping the top @var{n} items in registers
  @itemize
  @item
  is better than keeping @var{n-1} items, if @var{x>=n} and @var{y>=n},
- Line 1654
+ Line 3535
  Line 1654
  Line 3535
  @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{--}
+ @item Primitives with stack effects of the form @code{--}
- @var{out1}...@var{outy}} must store the TOS to the stack at the start.
+ @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{--}}
+ 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
  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.c}.
+ look at the resulting file @file{engine.s}.
+ @node System Architecture, Performance, Primitives, Internals
  @section System Architecture
  Our Forth system consists not only of primitives, but also of
- Line 1689
+ Line 3572
  Line 1689
  Line 3572
  same image file, and to make it easy for the users to use their image
  files on many machines. We currently need to create a different image
  file for machines with different cell sizes and different byte order
- (little- or big-endian)@footnote{We consider adding information to the
+ (little- or big-endian)@footnote{We are considering adding information to the
  image file that enables the loader to change the byte order.}.
  Forth code that is going to end up in a portable image file has to
- comply to some restrictions: addresses have to be stored in memory
+ comply to some restrictions: addresses have to be stored in memory with
- with special words (@code{A!}, @code{A,}, etc.) in order to make the
+ special words (@code{A!}, @code{A,}, etc.) in order to make the code
- code relocatable. Cells, floats, etc., have to be stored at the
+ relocatable. Cells, floats, etc., have to be stored at the natural
- natural alignment boundaries@footnote{E.g., store floats (8 bytes) at
+ alignment boundaries@footnote{E.g., store floats (8 bytes) at an address
- an address dividable by~8. This happens automatically in our system
+ dividable by~8. This happens automatically in our system when you use
- when you use the ANSI alignment words.}, in order to avoid alignment
+ the ANS Forth alignment words.}, in order to avoid alignment faults on
- faults on machines with stricter alignment. The image file is produced
+ machines with stricter alignment. The image file is produced by a
- by a metacompiler (@file{cross.fs}).
+ metacompiler (@file{cross.fs}).
  So, unlike the image file of Mitch Bradleys @code{cforth}, our image
  file is not directly executable, but has to undergo some manipulations
- Line 1709
+ Line 3592
  Line 1709
  Line 3592
  primitive calls with the appropriate code-field addresses (or code
  addresses in the case of direct threading).
+ @node  Performance,  , System Architecture, Internals
+ @section 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}.
+ However, this potential advantage of assembly language implementations
+ is not necessarily realized in complete Forth systems: We compared
+ Gforth (compiled with @code{gcc-2.6.3} and @code{-DFORCE_REG}) with
+ Win32Forth 1.2093 and LMI's NT Forth (Beta, May 1994), two systems
+ written in assembly, and with two systems written in C: PFE-0.9.11
+ (compiled with @code{gcc-2.6.3} with the default configuration for
+ Linux: @code{-O2 -fomit-frame-pointer -DUSE_REGS}) and ThisForth Beta
+ (compiled with gcc-2.6.3 -O3 -fomit-frame-pointer). We benchmarked
+ Gforth, PFE and ThisForth 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.
+ 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; 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               This-
+   time     Gforth     Forth     Forth       PFE     Forth
+ sieve        1.00      1.30      1.07      1.67      2.98
+ bubble       1.00      1.30      1.40      1.66
+ matmul       1.00      1.40      1.29      2.24
+ fib          1.00      1.44      1.26      1.82      2.82
+ @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{System Architecture}).
+ The speedup of Gforth over PFE and ThisForth can be easily explained
+ with the self-imposed restriction to standard C (although the measured
+ implementation of PFE uses a GNU C extension: global register
+ variables), which makes efficient threading impossible.  Moreover,
+ current C compilers have a hard time optimizing other aspects of the
+ ThisForth 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.
+ The numbers in this section have also been published in the paper
+ @cite{Translating Forth to Efficient C} by M. Anton Ertl and Martin
+ Maierhofer, presented at EuroForth '95. It is 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
+ numbers for Gforth on various machines in @file{Benchres}.
+ @node Bugs, Pedigree, Internals, Top
+ @chapter Bugs
+ Known bugs are described in the file BUGS in the Gforth distribution.
+ If you find a bug, please send a bug report to
+ @code{gforth-bugs@@mips.complang.tuwien.ac.at}. 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 @code{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 Pedigree, Word Index, Bugs, Top
+ @chapter Pedigree
+ 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
+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.
+ Laxen and 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
+. 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 developped 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 in the late 60s.
+ 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, Node Index, Pedigree, Top
+ @chapter Word Index
+ This index is as incomplete as the manual. Each word is listed with
+ stack effect and wordset.
+ @printindex fn
+ @node Node Index,  , Word Index, Top
+ @chapter Node Index
+ This index is even less complete than the manual.
  @contents
  @bye

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