Diff for /gforth/Attic/gforth.ds between versions 1.5 and 1.19

version 1.5, 1995/01/12 18:37:51 version 1.19, 1995/10/16 18:33:08
Line 2 Line 2
 @comment The source is gforth.ds, from which gforth.texi is generated  @comment The source is gforth.ds, from which gforth.texi is generated
 @comment %**start of header (This is for running Texinfo on a region.)  @comment %**start of header (This is for running Texinfo on a region.)
 @setfilename gforth.info  @setfilename gforth.info
 @settitle GNU Forth Manual  @settitle Gforth Manual
 @comment @setchapternewpage odd  @comment @setchapternewpage odd
 @comment %**end of header (This is for running Texinfo on a region.)  @comment %**end of header (This is for running Texinfo on a region.)
   
 @ifinfo  @ifinfo
 This file documents GNU Forth 0.0  This file documents Gforth 0.1
   
 Copyright @copyright{} 1994 GNU Forth Development Group  Copyright @copyright{} 1994 Gforth Development Group
   
      Permission is granted to make and distribute verbatim copies of       Permission is granted to make and distribute verbatim copies of
      this manual provided the copyright notice and this permission notice       this manual provided the copyright notice and this permission notice
Line 38  Copyright @copyright{} 1994 GNU Forth De Line 38  Copyright @copyright{} 1994 GNU Forth De
   
 @titlepage  @titlepage
 @sp 10  @sp 10
 @center @titlefont{GNU Forth Manual}  @center @titlefont{Gforth Manual}
 @sp 2  @sp 2
 @center for version 0.0  @center for version 0.1
 @sp 2  @sp 2
 @center Anton Ertl  @center Anton Ertl
   @sp 3
   @center This manual is under construction
   
 @comment  The following two commands start the copyright page.  @comment  The following two commands start the copyright page.
 @page  @page
 @vskip 0pt plus 1filll  @vskip 0pt plus 1filll
 Copyright @copyright{} 1994 GNU Forth Development Group  Copyright @copyright{} 1994 Gforth Development Group
   
 @comment !! Published by ... or You can get a copy of this manual ...  @comment !! Published by ... or You can get a copy of this manual ...
   
Line 72  Copyright @copyright{} 1994 GNU Forth De Line 74  Copyright @copyright{} 1994 GNU Forth De
   
 @node Top, License, (dir), (dir)  @node Top, License, (dir), (dir)
 @ifinfo  @ifinfo
 GNU Forth is a free implementation of ANS Forth available on many  Gforth is a free implementation of ANS Forth available on many
 personal machines. This manual corresponds to version 0.0.  personal machines. This manual corresponds to version 0.0.
 @end ifinfo  @end ifinfo
   
 @menu  @menu
 * License::                       * License::                     
 * Goals::                       About the GNU Forth Project  * Goals::                       About the Gforth Project
 * Other Books::                 Things you might want to read  * Other Books::                 Things you might want to read
 * Invocation::                  Starting GNU Forth  * Invocation::                  Starting Gforth
 * Words::                       Forth words available in GNU Forth  * Words::                       Forth words available in Gforth
 * ANS conformance::             Implementation-defined options etc.  * 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  * Internals::                   Implementation details
 * Bugs::                        How to report them  * Bugs::                        How to report them
 * Pedigree::                    Ancestors of GNU Forth  * Pedigree::                    Ancestors of Gforth
 * Word Index::                  An item for each Forth word  * Word Index::                  An item for each Forth word
 * Node Index::                  An item for each node  * Node Index::                  An item for each node
 @end menu  @end menu
Line 98  personal machines. This manual correspon Line 100  personal machines. This manual correspon
   
 @iftex  @iftex
 @unnumbered Preface  @unnumbered Preface
 This manual documents GNU Forth. The reader is expected to know  This manual documents Gforth. The reader is expected to know
 Forth. This manual is primarily a reference manual. @xref{Other Books}  Forth. This manual is primarily a reference manual. @xref{Other Books}
 for introductory material.  for introductory material.
 @end iftex  @end iftex
   
 @node    Goals, Other Books, License, Top  @node    Goals, Other Books, License, Top
 @comment node-name,     next,           previous, up  @comment node-name,     next,           previous, up
 @chapter Goals of GNU Forth  @chapter Goals of Gforth
 @cindex Goals  @cindex Goals
 The goal of the GNU Forth Project is to develop a standard model for  The goal of the Gforth Project is to develop a standard model for
 ANSI Forth. This can be split into several subgoals:  ANSI Forth. This can be split into several subgoals:
   
 @itemize @bullet  @itemize @bullet
 @item  @item
 GNU Forth should conform to the ANSI Forth standard.  Gforth should conform to the ANSI Forth standard.
 @item  @item
 It should be a model, i.e. it should define all the  It should be a model, i.e. it should define all the
 implementation-dependent things.  implementation-dependent things.
Line 121  It should become standard, i.e. widely a Line 123  It should become standard, i.e. widely a
 is the most difficult one.  is the most difficult one.
 @end itemize  @end itemize
   
 To achieve these goals GNU Forth should be  To achieve these goals Gforth should be
 @itemize @bullet  @itemize @bullet
 @item  @item
 Similar to previous models (fig-Forth, F83)  Similar to previous models (fig-Forth, F83)
Line 137  Free. Line 139  Free.
 Available on many machines/easy to port.  Available on many machines/easy to port.
 @end itemize  @end itemize
   
 Have we achieved these goals? GNU Forth conforms to the ANS Forth  Have we achieved these goals? Gforth conforms to the ANS Forth
 standard; it may be considered a model, but we have not yet documented  standard. It may be considered a model, but we have not yet documented
 which parts of the model are stable and which parts we are likely to  which parts of the model are stable and which parts we are likely to
 change; it certainly has not yet become a de facto standard. It has some  change. It certainly has not yet become a de facto standard. It has some
 similarities and some differences to previous models; It has some  similarities and some differences to previous models. It has some
 powerful features, but not yet everything that we envisioned; on RISCs  powerful features, but not yet everything that we envisioned. We
 it is as fast as interpreters programmed in assembly, on  certainly have achieved our execution speed goals (@pxref{Performance}).
 register-starved machines it is not so fast, but still faster than any  It is free and available on many machines.
 other C-based interpretive implementation; it is free and available on  
 many machines.  
   
 @node Other Books, Invocation, Goals, Top  @node Other Books, Invocation, Goals, Top
 @chapter Other books on ANS Forth  @chapter Other books on ANS Forth
   
 As the standard is relatively new, there are not many books out yet. It  As the standard is relatively new, there are not many books out yet. It
 is not recommended to learn Forth by using GNU Forth and a book that is  is not recommended to learn Forth by using Gforth and a book that is
 not written for ANS Forth, as you will not know your mistakes from the  not written for ANS Forth, as you will not know your mistakes from the
 deviations of the book.  deviations of the book.
   
 There is, of course, the standard, the definite reference if you want to  There is, of course, the standard, the definite reference if you want to
 write ANS Forth programs. It will be available in printed form from  write ANS Forth programs. It is available in printed form from the
 Global Engineering Documents !! somtime in spring or summer 1994. If you  National Standards Institute Sales Department (Tel.: USA (212) 642-4900;
 are lucky, you can still get dpANS6 (the draft that was approved as  Fax.: USA (212) 302-1286) as document @cite{X3.215-1994} for about $200. You
 standard) by aftp from ftp.uu.net:/vendor/minerva/x3j14.  can also get it from Global Engineering Documents (Tel.: USA (800)
   854-7179; Fax.: (303) 843-9880) for about $300.
   
   @cite{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
   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 (!! Publisher) is an
 introductory book based on a draft version of the standard. It does not  introductory book based on a draft version of the standard. It does not
Line 173  other languages should find it ok. Line 180  other languages should find it ok.
 @chapter Invocation  @chapter Invocation
   
 You will usually just say @code{gforth}. In many other cases the default  You will usually just say @code{gforth}. In many other cases the default
 GNU Forth image will be invoked like this:  Gforth image will be invoked like this:
   
 @example  @example
 gforth [files] [-e forth-code]  gforth [files] [-e forth-code]
Line 269  then in @file{~}, then in the normal pat Line 276  then in @file{~}, then in the normal pat
 * Blocks::                        * Blocks::                      
 * Other I/O::                     * Other I/O::                   
 * Programming Tools::             * Programming Tools::           
   * Assembler and Code words::    
 * Threading Words::               * Threading Words::             
 @end menu  @end menu
   
Line 285  that has become a de-facto standard for Line 293  that has become a de-facto standard for
   
 @table @var  @table @var
 @item word  @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  @item Stack effect
 The stack effect is written in the notation @code{@var{before} --  The stack effect is written in the notation @code{@var{before} --
 @var{after}}, where @var{before} and @var{after} describe the top of  @var{after}}, where @var{before} and @var{after} describe the top of
 stack entries before and after the execution of the word. The rest of  stack entries before and after the execution of the word. The rest of
 the stack is not touched by the word. The top of stack is rightmost,  the stack is not touched by the word. The top of stack is rightmost,
 i.e., a stack sequence is written as it is typed in. Note that GNU Forth  i.e., a stack sequence is written as it is typed in. Note that Gforth
 uses a separate floating point stack, but a unified stack  uses a separate floating point stack, but a unified stack
 notation. Also, return stack effects are not shown in @var{stack  notation. Also, return stack effects are not shown in @var{stack
 effect}, but in @var{Description}. The name of a stack item describes  effect}, but in @var{Description}. The name of a stack item describes
 the type and/or the function of the item. See below for a discussion of  the type and/or the function of the item. See below for a discussion of
 the types.  the types.
   
   All words have two stack effects: A compile-time stack effect and a
   run-time stack effect. The compile-time stack-effect of most words is
   @var{ -- }. If the compile-time stack-effect of a word deviates from
   this standard behaviour, or the word does other unusual things at
   compile time, both stack effects are shown; otherwise only the run-time
   stack effect is shown.
   
 @item pronunciation  @item pronunciation
 How the word is pronounced  How the word is pronounced
   
Line 309  system need not support all of them. So, Line 324  system need not support all of them. So,
 uses the more portable it will be in theory. However, we suspect that  uses the more portable it will be in theory. However, we suspect that
 most ANS Forth systems on personal machines will feature all  most ANS Forth systems on personal machines will feature all
 wordsets. Words that are not defined in the ANS standard have  wordsets. Words that are not defined in the ANS standard have
 @code{gforth} as wordset.  @code{gforth} or @code{gforth-internal} as wordset. @code{gforth}
   describes words that will work in future releases of Gforth;
   @code{gforth-internal} words are more volatile. Environmental query
   strings are also displayed like words; you can recognize them by the
   @code{environment} in the wordset field.
   
 @item Description  @item Description
 A description of the behaviour of the word.  A description of the behaviour of the word.
Line 409  doc-sm/rem Line 428  doc-sm/rem
   
 @node Double precision, Floating Point, Mixed precision, Arithmetic  @node Double precision, Floating Point, Mixed precision, Arithmetic
 @subsection Double precision  @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-d-  doc-d-
 doc-dnegate  doc-dnegate
Line 419  doc-dmax Line 443  doc-dmax
 @node Floating Point,  , Double precision, Arithmetic  @node Floating Point,  , Double precision, Arithmetic
 @subsection Floating Point  @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
   10, irrespective of the value of @code{BASE}. If @code{BASE} contains a
   value greater then 14, the @code{E} may be interpreted as digit and the
   number will be interpreted as integer, unless it has a signed exponent
   (both @code{+} and @code{-} are allowed as signs).
   
 Angles in floating point operations are given in radians (a full circle  Angles in floating point operations are given in radians (a full circle
 has 2 pi radians). Note, that gforth has a separate floating point  has 2 pi radians). Note, that Gforth has a separate floating point
 stack, but we use the unified notation.  stack, but we use the unified notation.
   
 Floating point numbers have a number of unpleasant surprises for the  Floating point numbers have a number of unpleasant surprises for the
Line 428  unwary (e.g., floating point addition is Line 465  unwary (e.g., floating point addition is
 for the wary. You should not use them unless you know what you are doing  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  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  want to learn about the problems of floating point numbers (and how to
 avoid them), you might start with @cite{Goldberg, What every computer  avoid them), you might start with @cite{David Goldberg, What Every
 scientist should know about floating-point numbers, Computing Surveys  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-
Line 449  doc-fexpm1 Line 486  doc-fexpm1
 doc-fln  doc-fln
 doc-flnp1  doc-flnp1
 doc-flog  doc-flog
   doc-falog
 doc-fsin  doc-fsin
 doc-fcos  doc-fcos
 doc-fsincos  doc-fsincos
Line 467  doc-fatanh Line 505  doc-fatanh
 @node Stack Manipulation, Memory access, Arithmetic, Words  @node Stack Manipulation, Memory access, Arithmetic, Words
 @section Stack Manipulation  @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  addresses, and double cells, a floating point stack for floating point
 numbers, a return stack for storing the return addresses of colon  numbers, a return stack for storing the return addresses of colon
 definitions and other data, and a locals stack for storing local  definitions and other data, and a locals stack for storing local
Line 593  must only occur at specific addresses; e Line 631  must only occur at specific addresses; e
 accessed at addresses divisible by 4. Even if a machine allows unaligned  accessed at addresses divisible by 4. Even if a machine allows unaligned
 accesses, it can usually perform aligned accesses faster.   accesses, it can usually perform aligned accesses faster. 
   
 For the performance-concious: alignment operations are usually only  For the performance-conscious: alignment operations are usually only
 necessary during the definition of a data structure, not during the  necessary during the definition of a data structure, not during the
 (more frequent) accesses to it.  (more frequent) accesses to it.
   
Line 603  char-aligned have no use in the standard Line 641  char-aligned have no use in the standard
 created.  created.
   
 The standard guarantees that addresses returned by @code{CREATE}d words  The standard guarantees that addresses returned by @code{CREATE}d words
 are cell-aligned; in addition, gforth guarantees that these addresses  are cell-aligned; in addition, Gforth guarantees that these addresses
 are aligned for all purposes.  are aligned for all purposes.
   
   Note that the standard defines a word @code{char}, which has nothing to
   do with address arithmetic.
   
 doc-chars  doc-chars
 doc-char+  doc-char+
 doc-cells  doc-cells
Line 624  doc-dfloats Line 665  doc-dfloats
 doc-dfloat+  doc-dfloat+
 doc-dfalign  doc-dfalign
 doc-dfaligned  doc-dfaligned
   doc-maxalign
   doc-maxaligned
   doc-cfalign
   doc-cfaligned
 doc-address-unit-bits  doc-address-unit-bits
   
 @node Memory block access,  , Address arithmetic, Memory access  @node Memory block access,  , Address arithmetic, Memory access
Line 782  There are several variations on the coun Line 827  There are several variations on the coun
   
 @code{LEAVE} leaves the innermost counted loop immediately.  @code{LEAVE} leaves the innermost counted loop immediately.
   
   If @var{start} is greater than @var{limit}, a @code{?DO} loop is entered
   (and @code{LOOP} iterates until they become equal by wrap-around
   arithmetic). This behaviour is usually not what you want. Therefore,
   Gforth offers @code{+DO} and @code{U+DO} (as replacements for
   @code{?DO}), which do not enter the loop if @var{start} is greater than
   @var{limit}; @code{+DO} is for signed loop parameters, @code{U+DO} for
   unsigned loop parameters. 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  @code{LOOP} can be replaced with @code{@var{n} +LOOP}; this updates the
 index by @var{n} instead of by 1. The loop is terminated when the border  index by @var{n} instead of by 1. The loop is terminated when the border
 between @var{limit-1} and @var{limit} is crossed. E.g.:  between @var{limit-1} and @var{limit} is crossed. E.g.:
   
 @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:  The behaviour of @code{@var{n} +LOOP} is peculiar when @var{n} is negative:
   
Line 796  The behaviour of @code{@var{n} +LOOP} is Line 855  The behaviour of @code{@var{n} +LOOP} is
   
 @code{ 0 0 ?DO  i .  -1 +LOOP}  prints nothing  @code{ 0 0 ?DO  i .  -1 +LOOP}  prints nothing
   
 Therefore we recommend avoiding using @code{@var{n} +LOOP} with negative  Therefore we recommend avoiding @code{@var{n} +LOOP} with negative
 @var{n}. One alternative is @code{@var{n} S+LOOP}, where the negative  @var{n}. One alternative is @code{@var{u} -LOOP}, which reduces the
 case behaves symmetrical to the positive case:  index by @var{u} each iteration. The loop is terminated when the border
   between @var{limit+1} and @var{limit} is crossed. Gforth also provides
   @code{-DO} and @code{U-DO} for down-counting loops. E.g.:
   
 @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:
   
 The loop is terminated when the border between @var{limit@minus{}sgn(n)} and  @code{-2 0 -DO  i .  -1 S+LOOP}  prints @code{0 -1}
 @var{limit} is crossed. However, @code{S+LOOP} is not part of the ANS  
 Forth standard.  The loop is terminated when the border between @var{limit@minus{}sgn(n)}
   and @var{limit} is crossed. Unfortunately, neither @code{-LOOP} nor
 @code{?DO} can be replaced by @code{DO}. @code{DO} enters the loop even  @code{S+LOOP} are part of the ANS Forth standard, and they are not easy
 when the start and the limit value are equal. We do not recommend using  to implement using standard words. If you want to write standard
 @code{DO}. It will just give you maintenance troubles.  programs, just avoid counting down.
   
   @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{UNLOOP} is used to prepare for an abnormal loop exit, e.g., via
 @code{EXIT}. @code{UNLOOP} removes the loop control parameters from the  @code{EXIT}. @code{UNLOOP} removes the loop control parameters from the
Line 826  FOR Line 896  FOR
 NEXT  NEXT
 @end example  @end example
 This is the preferred loop of native code compiler writers who are too  This is the preferred loop of native code compiler writers who are too
 lazy to optimize @code{?DO} loops properly. In GNU Forth, this loop  lazy to optimize @code{?DO} loops properly. In Gforth, this loop
 iterates @var{n+1} times; @code{i} produces values starting with @var{n}  iterates @var{n+1} times; @code{i} produces values starting with @var{n}
 and ending with 0. Other Forth systems may behave differently, even if  and ending with 0. Other Forth systems may behave differently, even if
 they support @code{FOR} loops.  they support @code{FOR} loops.
Line 837  they support @code{FOR} loops. Line 907  they support @code{FOR} loops.
 ANS Forth permits and supports using control structures in a non-nested  ANS Forth permits and supports using control structures in a non-nested
 way. Information about incomplete control structures is stored on the  way. Information about incomplete control structures is stored on the
 control-flow stack. This stack may be implemented on the Forth data  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}  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  entry represents a backward branch target. A few words are the basis for
Line 853  doc-again Line 923  doc-again
 doc-cs-pick  doc-cs-pick
 doc-cs-roll  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  currently take three (this may change in the future). Therefore it is a
 really good idea to manipulate the control flow stack with  really good idea to manipulate the control flow stack with
 @code{cs-pick} and @code{cs-roll}, not with data stack manipulation  @code{cs-pick} and @code{cs-roll}, not with data stack manipulation
Line 868  doc-repeat Line 938  doc-repeat
 Counted loop words constitute a separate group of words:  Counted loop words constitute a separate group of words:
   
 doc-?do  doc-?do
   doc-+do
   doc-u+do
   doc--do
   doc-u-do
 doc-do  doc-do
 doc-for  doc-for
 doc-loop  doc-loop
 doc-s+loop  doc-s+loop
 doc-+loop  doc-+loop
   doc--loop
 doc-next  doc-next
 doc-leave  doc-leave
 doc-?leave  doc-?leave
 doc-unloop  doc-unloop
 doc-undo  doc-done
   
 The standard does not allow using @code{cs-pick} and @code{cs-roll} on  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  @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  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  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  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  Another group of control structure words are
   
Line 943  necessary to define them. Line 1018  necessary to define them.
 @subsection Calls and returns  @subsection Calls and returns
   
 A definition can be called simply be writing the name of the  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  doc-exit
   
Line 969  locals wordset, but also our own, more p Line 1045  locals wordset, but also our own, more p
 implemented the ANS Forth locals wordset through our locals wordset).  implemented the ANS Forth locals wordset through our locals wordset).
   
 @menu  @menu
 * gforth locals::                 * Gforth locals::               
 * ANS Forth locals::              * ANS Forth locals::            
 @end menu  @end menu
   
 @node gforth locals, ANS Forth locals, Locals, Locals  @node Gforth locals, ANS Forth locals, Locals, Locals
 @subsection gforth locals  @subsection Gforth locals
   
 Locals can be defined with  Locals can be defined with
   
Line 1017  The name of the local may be preceded by Line 1093  The name of the local may be preceded by
  Ar Bi f* Ai Br f* f+ ;   Ar Bi f* Ai Br f* f+ ;
 @end example  @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{D:}, @code{D^}), floats (@code{F:}, @code{F^}) and characters
 (@code{C:}, @code{C^}) in two flavours: a value-flavoured local (defined  (@code{C:}, @code{C^}) in two flavours: a value-flavoured local (defined
 with @code{W:}, @code{D:} etc.) produces its value and can be changed  with @code{W:}, @code{D:} etc.) produces its value and can be changed
Line 1037  locals are initialized with values from Line 1113  locals are initialized with values from
 Currently there is no way to define locals with user-defined data  Currently there is no way to define locals with user-defined data
 structures, but we are working on it.  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  @menu
 * Where are locals visible by name?::    * Where are locals visible by name?::  
 * How long do locals live? ::     * How long do locals live?::    
 * Programming Style::             * Programming Style::           
 * Implementation::                * Implementation::              
 @end menu  @end menu
   
 @node Where are locals visible by name?, How long do locals live?, gforth locals, gforth locals  @node Where are locals visible by name?, How long do locals live?, Gforth locals, Gforth locals
 @subsubsection Where are locals visible by name?  @subsubsection Where are locals visible by name?
   
 Basically, the answer is that locals are visible where you would expect  Basically, the answer is that locals are visible where you would expect
Line 1168  If the @code{BEGIN} is not reachable fro Line 1245  If the @code{BEGIN} is not reachable fro
 @code{AHEAD} or @code{EXIT}), the compiler cannot even make an  @code{AHEAD} or @code{EXIT}), the compiler cannot even make an
 optimistic guess, as the locals visible after the @code{BEGIN} may be  optimistic guess, as the locals visible after the @code{BEGIN} may be
 defined later. Therefore, the compiler assumes that no locals are  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  @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  doc-assume-live
   
Line 1204  WHILE Line 1282  WHILE
 REPEAT  REPEAT
 @end example  @end example
   
 @node How long do locals live?, Programming Style, Where are locals visible by name?, gforth locals  @node How long do locals live?, Programming Style, Where are locals visible by name?, Gforth locals
 @subsubsection How long do locals live?  @subsubsection How long do locals live?
   
 The right answer for the lifetime question would be: A local lives at  The right answer for the lifetime question would be: A local lives at
Line 1218  languages (e.g., C): The local lives onl Line 1296  languages (e.g., C): The local lives onl
 afterwards its address is invalid (and programs that access it  afterwards its address is invalid (and programs that access it
 afterwards are erroneous).  afterwards are erroneous).
   
 @node Programming Style, Implementation, How long do locals live?, gforth locals  @node Programming Style, Implementation, How long do locals live?, Gforth locals
 @subsubsection Programming Style  @subsubsection Programming Style
   
 The freedom to define locals anywhere has the potential to change  The freedom to define locals anywhere has the potential to change
Line 1232  write the items in the order you want. Line 1310  write the items in the order you want.
 This seems a little far-fetched and eliminating stack manipulations is  This seems a little far-fetched and eliminating stack manipulations is
 unlikely to become a conscious programming objective. Still, the number  unlikely to become a conscious programming objective. Still, the number
 of stack manipulations will be reduced dramatically if local variables  of stack manipulations will be reduced dramatically if local variables
 are used liberally (e.g., compare @code{max} in @ref{gforth locals} with  are used liberally (e.g., compare @code{max} in @ref{Gforth locals} with
 a traditional implementation of @code{max}).  a traditional implementation of @code{max}).
   
 This shows one potential benefit of locals: making Forth programs more  This shows one potential benefit of locals: making Forth programs more
Line 1287  are initialized with the right value for Line 1365  are initialized with the right value for
 Here it is clear from the start that @code{s1} has a different value  Here it is clear from the start that @code{s1} has a different value
 in every loop iteration.  in every loop iteration.
   
 @node Implementation,  , Programming Style, gforth locals  @node Implementation,  , Programming Style, Gforth locals
 @subsubsection Implementation  @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  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  also eliminates the problems and restrictions of using the return stack
 as locals stack. Like the other stacks, the locals stack grows toward  as locals stack. Like the other stacks, the locals stack grows toward
Line 1311 local0 Line 1389 local0
 compile the right specialized version, or the general version, as  compile the right specialized version, or the general version, as
 appropriate:  appropriate:
   
 doc-compile-@@local  doc-compile-@local
 doc-compile-f@@local  doc-compile-f@local
 doc-compile-lp+!  doc-compile-lp+!
   
 Combinations of conditional branches and @code{lp+!#} like  Combinations of conditional branches and @code{lp+!#} like
Line 1325  area and @code{@}} switches it back and Line 1403  area and @code{@}} switches it back and
 initializing code. @code{W:} etc.@ are normal defining words. This  initializing code. @code{W:} etc.@ are normal defining words. This
 special area is cleared at the start of every colon definition.  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  definition of locals without type specifiers: every wordlist (aka
 vocabulary) has its own methods for searching  vocabulary) has its own methods for searching
 etc. (@pxref{Wordlists}). For the present purpose we defined a wordlist  etc. (@pxref{Wordlists}). For the present purpose we defined a wordlist
Line 1415  this may lead to increased space needs f Line 1493  this may lead to increased space needs f
 usually less than reclaiming this space would cost in code size.  usually less than reclaiming this space would cost in code size.
   
   
 @node ANS Forth locals,  , gforth locals, Locals  @node ANS Forth locals,  , Gforth locals, Locals
 @subsection ANS Forth locals  @subsection ANS Forth locals
   
 The ANS Forth locals wordset does not define a syntax for locals, but  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  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.:  wordset, i.e.:
   
 @example  @example
Line 1436  restrictions are: Line 1514  restrictions are:
   
 @itemize @bullet  @itemize @bullet
 @item  @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  @item
 Locals can be defined only outside control structures.  Locals can be defined only outside control structures.
 @item  @item
 Locals can interfere with explicit usage of the return stack. For the  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  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  purpose of this rule is to make locals implementation on the return
 stack easier.  stack easier.
 @item  @item
Line 1453  Locals defined in this way behave like @ Line 1531  Locals defined in this way behave like @
 (@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}.  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  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  another ANS Forth system, use @file{anslocal.fs} to implement the syntax
 on the other system.  on the other system.
Line 1468  doc-(local) Line 1546  doc-(local)
   
 The ANS Forth locals extension wordset defines a syntax, but it is so  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  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  problem with this syntax is that the locals are defined in an order
 reversed with respect to the standard stack comment notation, making  reversed with respect to the standard stack comment notation, making
 programs harder to read, and easier to misread and miswrite. The only  programs harder to read, and easier to misread and miswrite. The only
Line 1478  locals wordset. Line 1556  locals wordset.
 @node Defining Words, Wordlists, Locals, Words  @node Defining Words, Wordlists, Locals, Words
 @section Defining Words  @section Defining Words
   
   @menu
   * Values::                      
   @end menu
   
 @node Values,  , Defining Words, Defining Words  @node Values,  , Defining Words, Defining Words
 @subsection Values  @subsection Values
   
Line 1493  locals wordset. Line 1575  locals wordset.
 @node Other I/O, Programming Tools, Blocks, Words  @node Other I/O, Programming Tools, Blocks, Words
 @section Other I/O  @section Other I/O
   
 @node Programming Tools, Threading Words, Other I/O, Words  @node Programming Tools, Assembler and Code words, Other I/O, Words
 @section Programming Tools  @section Programming Tools
   
 @menu  @menu
Line 1538  doc-printdebugline Line 1620  doc-printdebugline
   
 It is a good idea to make your programs self-checking, in particular, if  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  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  never zero) that may become wrong during maintenance. Gforth supports
 assertions for this purpose. They are used like this:  assertions for this purpose. They are used like this:
   
 @example  @example
Line 1561  debugging, we want more checking, in pro Line 1643  debugging, we want more checking, in pro
 for speed. Therefore, assertions can be turned off, i.e., the assertion  for speed. Therefore, assertions can be turned off, i.e., the assertion
 becomes a comment. Depending on the importance of an assertion and the  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  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  keep others turned on. Gforth provides several levels of assertions for
 this purpose:  this purpose:
   
 doc-assert0(  doc-assert0(
Line 1592  If there is interest, we will introduce Line 1674  If there is interest, we will introduce
 intend to @code{catch} a specific condition, using @code{throw} is  intend to @code{catch} a specific condition, using @code{throw} is
 probably more appropriate than an assertion).  probably more appropriate than an assertion).
   
 @node Threading Words,  , Programming Tools, Words  @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  @section Threading Words
   
 These words provide access to code addresses and other threading stuff  These words provide access to code addresses and other threading stuff
 in gforth (and, possibly, other interpretive Forths). It more or less  in Gforth (and, possibly, other interpretive Forths). It more or less
 abstracts away the differences between direct and indirect threading  abstracts away the differences between direct and indirect threading
 (and, for direct threading, the machine dependences). However, at  (and, for direct threading, the machine dependences). However, at
 present this wordset is still inclomplete. It is also pretty low-level;  present this wordset is still inclomplete. It is also pretty low-level;
Line 1610  doc-does-code! Line 1728  doc-does-code!
 doc-does-handler!  doc-does-handler!
 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  @node ANS conformance, Model, Words, Top
 @chapter ANS conformance  @chapter ANS conformance
   
 @node Model, Emacs and GForth, ANS conformance, Top  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
   8). 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
   8-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
   36@minus{}41. There is no way to input many of the larger digits.
   
   @item display after input terminates in @code{ACCEPT} and @code{EXPECT}:
   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:
   31
   
   @item maximum string length for @code{ENVIRONMENT?}, in characters:
   31
   
   @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
   2**bits-per-cell for single arithmetic and 4**bits-per-cell for double
   arithmetic (with appropriate mapping for signed types). Division by zero
   typically results in a @code{-55 throw} (floatingpoint unidentified
   fault), although a @code{-10 throw} (divide by zero) would be more
   appropriate.
   
   @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
   2**bits-per-cell for single arithmetic and 4**bits-per-cell for double
   arithmetic (with appropriate mapping for signed types). Division by zero
   typically results in a @code{-55 throw} (floatingpoint unidentified
   fault), although a @code{-10 throw} (divide by zero) would be more
   appropriate. @code{convert} and @code{>number} currently overflow
   silently.
   
   @item reading from an empty data or return stack:
   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{\}:
   64 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
   488} on my system.
   @end table
   
   @c =====================================================================
   @node The optional Facility word set, The optional File-Access word set, The optional Exception word set, ANS conformance
   @section The optional Facility word set
   @c =====================================================================
   
   @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"}:
   1
   
   @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  @chapter Model
   
 @node Emacs and GForth, Internals, Model, Top  @node Emacs and Gforth, Internals, Model, Top
 @chapter Emacs and GForth  @chapter Emacs and Gforth
   
 GForth comes with @file{gforth.el}, an improved version of  Gforth comes with @file{gforth.el}, an improved version of
 @file{forth.el} by Goran Rydqvist (icluded in the TILE package). The  @file{forth.el} by Goran Rydqvist (icluded in the TILE package). The
 improvements are a better (but still not perfect) handling of  improvements are a better (but still not perfect) handling of
 indentation. I have also added comment paragraph filling (@kbd{M-q}),  indentation. I have also added comment paragraph filling (@kbd{M-q}),
 commenting (@kbd{C-x \}) and uncommenting (@kbd{C-x |}) regions and  commenting (@kbd{C-x \}) and uncommenting (@kbd{C-u C-x \}) regions and
 removing debugging tracers (@kbd{C-x ~}). I left the stuff I do not use  removing debugging tracers (@kbd{C-x ~}, @pxref{Debugging}). I left the
 alone, even though some of it only makes sense for TILE. To get a  stuff I do not use alone, even though some of it only makes sense for
 description of these features, enter Forth mode and type @kbd{C-h m}.  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  In addition, Gforth supports Emacs quite well: The source code locations
 given in error messages, debugging output (from @code{~~}) and failed  given in error messages, debugging output (from @code{~~}) and failed
 assertion messages are in the right format for Emacs' compilation mode  assertion messages are in the right format for Emacs' compilation mode
 (@pxref{Compilation, , Running Compilations under Emacs, emacs, Emacs  (@pxref{Compilation, , Running Compilations under Emacs, emacs, Emacs
Line 1640  Also, if you @code{include} @file{etags. Line 2793  Also, if you @code{include} @file{etags.
 (@pxref{Tags, , Tags Tables, emacs, Emacs Manual}) will be produced that  (@pxref{Tags, , Tags Tables, emacs, Emacs Manual}) will be produced that
 contains the definitions of all words defined afterwards. You can then  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  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  several tags files at the same time (e.g., one for the Gforth sources
 and one for your program).  and one for your program).
   
 To get all these benefits, add the following lines to your @file{.emacs}  To get all these benefits, add the following lines to your @file{.emacs}
Line 1651  file: Line 2804  file:
 (setq auto-mode-alist (cons '("\\.fs\\'" . forth-mode) auto-mode-alist))  (setq auto-mode-alist (cons '("\\.fs\\'" . forth-mode) auto-mode-alist))
 @end example  @end example
   
 @node Internals, Bugs, Emacs and GForth, Top  @node Internals, Bugs, Emacs and Gforth, Top
 @chapter Internals  @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.
   
 @menu  @menu
 * Portability::                   * Portability::                 
 * Threading::                     * Threading::                   
 * Primitives::                    * Primitives::                  
 * System Architecture::           * System Architecture::         
   * Performance::                 
 @end menu  @end menu
   
 @node Portability, Threading, Internals, Internals  @node Portability, Threading, Internals, Internals
Line 1693  Double-Word Integers, gcc.info, GNU C Ma Line 2847  Double-Word Integers, gcc.info, GNU C Ma
 double numbers. GNU C is available for free on all important (and many  double numbers. GNU C is available for free on all important (and many
 unimportant) UNIX machines, VMS, 80386s running MS-DOS, the Amiga, and  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  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  Writing in a portable language has the reputation of producing code that
 is slower than assembly. For our Forth engine we repeatedly looked at  is slower than assembly. For our Forth engine we repeatedly looked at
Line 1986  To see what assembly code is produced fo Line 3138  To see what assembly code is produced fo
 with your compiler and your flag settings, type @code{make engine.s} and  with your compiler and your flag settings, type @code{make engine.s} and
 look at the resulting file @file{engine.s}.  look at the resulting file @file{engine.s}.
   
 @node System Architecture,  , Primitives, Internals  @node System Architecture, Performance, Primitives, Internals
 @section System Architecture  @section System Architecture
   
 Our Forth system consists not only of primitives, but also of  Our Forth system consists not only of primitives, but also of
Line 2009  possible, because we do not want to dist Line 3161  possible, because we do not want to dist
 same image file, and to make it easy for the users to use their image  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  files on many machines. We currently need to create a different image
 file for machines with different cell sizes and different byte order  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.}.  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  Forth code that is going to end up in a portable image file has to
Line 2029  at run-time. The loader also has to repl Line 3181  at run-time. The loader also has to repl
 primitive calls with the appropriate code-field addresses (or code  primitive calls with the appropriate code-field addresses (or code
 addresses in the case of direct threading).  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 benchmark 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.
   
 @node Bugs, Pedigree, Internals, Top  @node Bugs, Pedigree, Internals, Top
 @chapter Bugs  @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 !!. 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 (!! a way to find them out), 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  @node Pedigree, Word Index, Bugs, Top
 @chapter Pedigree  @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 child of VolksForth.
   
   VolksForth descends from F83. !! Authors? When?
   
   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
   1979. Dean Sanderson and Bill Ragsdale developed the original
   implementation of fig-Forth based on microForth.
   
   !! microForth pedigree
   
   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  @node Word Index, Node Index, Pedigree, Top
 @chapter Word Index  @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  @node Node Index,  , Word Index, Top
 @chapter Node Index  @chapter Node Index
   
   This index is even less complete than the manual.
   
 @contents  @contents
 @bye  @bye
   

Removed from v.1.5  
changed lines
  Added in v.1.19


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