--- gforth/Attic/gforth.ds 1995/01/10 18:57:43 1.4 +++ gforth/Attic/gforth.ds 1995/10/07 17:38:14 1.18 @@ -2,14 +2,14 @@ @comment The source is gforth.ds, from which gforth.texi is generated @comment %**start of header (This is for running Texinfo on a region.) @setfilename gforth.info -@settitle GNU Forth Manual +@settitle Gforth Manual @comment @setchapternewpage odd @comment %**end of header (This is for running Texinfo on a region.) @ifinfo -This file documents GNU Forth 0.0 +This file documents Gforth 0.1 -Copyright @copyright{} 1994 GNU Forth Development Group +Copyright @copyright{} 1994 Gforth Development Group Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice @@ -38,16 +38,18 @@ Copyright @copyright{} 1994 GNU Forth De @titlepage @sp 10 -@center @titlefont{GNU Forth Manual} +@center @titlefont{Gforth Manual} @sp 2 -@center for version 0.0 +@center for version 0.1 @sp 2 @center Anton Ertl +@sp 3 +@center This manual is under construction @comment The following two commands start the copyright page. @page @vskip 0pt plus 1filll -Copyright @copyright{} 1994 GNU Forth Development Group +Copyright @copyright{} 1994 Gforth Development Group @comment !! Published by ... or You can get a copy of this manual ... @@ -72,22 +74,22 @@ Copyright @copyright{} 1994 GNU Forth De @node Top, License, (dir), (dir) @ifinfo -GNU Forth is a free implementation of ANS Forth available on many +Gforth is a free implementation of ANS Forth available on many personal machines. This manual corresponds to version 0.0. @end ifinfo @menu * License:: -* Goals:: About the GNU Forth Project +* Goals:: About the Gforth Project * Other Books:: Things you might want to read -* Invocation:: Starting GNU Forth -* Words:: Forth words available in GNU Forth +* Invocation:: Starting Gforth +* Words:: Forth words available in Gforth * ANS conformance:: Implementation-defined options etc. -* Model:: The abstract machine of GNU Forth -* Emacs and GForth:: The GForth Mode +* Model:: The abstract machine of Gforth +* Emacs and Gforth:: The Gforth Mode * Internals:: Implementation details * Bugs:: How to report them -* Pedigree:: Ancestors of GNU Forth +* Pedigree:: Ancestors of Gforth * Word Index:: An item for each Forth word * Node Index:: An item for each node @end menu @@ -98,21 +100,21 @@ personal machines. This manual correspon @iftex @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} for introductory material. @end iftex @node Goals, Other Books, License, Top @comment node-name, next, previous, up -@chapter Goals of GNU Forth +@chapter Goals of Gforth @cindex Goals -The goal of the GNU Forth Project is to develop a standard model for +The goal of the Gforth Project is to develop a standard model for ANSI Forth. This can be split into several subgoals: @itemize @bullet @item -GNU Forth should conform to the ANSI Forth standard. +Gforth should conform to the ANSI Forth standard. @item It should be a model, i.e. it should define all the implementation-dependent things. @@ -121,7 +123,7 @@ It should become standard, i.e. widely a is the most difficult one. @end itemize -To achieve these goals GNU Forth should be +To achieve these goals Gforth should be @itemize @bullet @item Similar to previous models (fig-Forth, F83) @@ -137,22 +139,20 @@ Free. Available on many machines/easy to port. @end itemize -Have we achieved these goals? GNU Forth conforms to the ANS Forth -standard; it may be considered a model, but we have not yet documented +Have we achieved these goals? Gforth conforms to the ANS Forth +standard. It may be considered a model, but we have not yet documented which parts of the model are stable and which parts we are likely to -change; it certainly has not yet become a de facto standard. It has some -similarities and some differences to previous models; It has some -powerful features, but not yet everything that we envisioned; on RISCs -it is as fast as interpreters programmed in assembly, on -register-starved machines it is not so fast, but still faster than any -other C-based interpretive implementation; it is free and available on -many machines. +change. It certainly has not yet become a de facto standard. It has some +similarities and some differences to previous models. It has some +powerful features, but not yet everything that we envisioned. We +certainly have achieved our execution speed goals (@pxref{Performance}). +It is free and available on many machines. @node Other Books, Invocation, Goals, Top @chapter Other books on ANS Forth As the standard is relatively new, there are not many books out yet. It -is not recommended to learn Forth by using GNU Forth and a book that is +is not recommended to learn Forth by using Gforth and a book that is not written for ANS Forth, as you will not know your mistakes from the deviations of the book. @@ -173,7 +173,7 @@ other languages should find it ok. @chapter Invocation You will usually just say @code{gforth}. In many other cases the default -GNU Forth image will be invoked like this: +Gforth image will be invoked like this: @example gforth [files] [-e forth-code] @@ -269,6 +269,7 @@ then in @file{~}, then in the normal pat * Blocks:: * Other I/O:: * Programming Tools:: +* Assembler and Code words:: * Threading Words:: @end menu @@ -285,15 +286,15 @@ that has become a de-facto standard for @table @var @item word -The name of the word. BTW, GNU Forth is case insensitive, so you can -type the words in in lower case. +The name of the word. BTW, Gforth is case insensitive, so you can +type the words in in lower case (However, @pxref{core-idef}). @item Stack effect The stack effect is written in the notation @code{@var{before} -- @var{after}}, where @var{before} and @var{after} describe the top of stack entries before and after the execution of the word. The rest of the stack is not touched by the word. The top of stack is rightmost, -i.e., a stack sequence is written as it is typed in. Note that GNU Forth +i.e., a stack sequence is written as it is typed in. Note that Gforth uses a separate floating point stack, but a unified stack notation. Also, return stack effects are not shown in @var{stack effect}, but in @var{Description}. The name of a stack item describes @@ -409,6 +410,11 @@ doc-sm/rem @node Double precision, Floating Point, Mixed precision, Arithmetic @subsection Double precision + +The outer (aka text) interpreter converts numbers containing a dot into +a double precision number. Note that only numbers with the dot as last +character are standard-conforming. + doc-d+ doc-d- doc-dnegate @@ -419,8 +425,21 @@ doc-dmax @node Floating Point, , Double precision, Arithmetic @subsection Floating Point +The format of floating point numbers recognized by the outer (aka text) +interpreter is: a signed decimal number, possibly containing a decimal +point (@code{.}), followed by @code{E} or @code{e}, optionally followed +by a signed integer (the exponent). E.g., @code{1e} ist the same as +@code{+1.0e+1}. Note that a number without @code{e} +is not interpreted as floating-point number, but as double (if the +number contains a @code{.}) or single precision integer. Also, +conversions between string and floating point numbers always use base +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 -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. Floating point numbers have a number of unpleasant surprises for the @@ -428,9 +447,9 @@ unwary (e.g., floating point addition is for the wary. You should not use them unless you know what you are doing or you don't care that the results you get are totally bogus. If you want to learn about the problems of floating point numbers (and how to -avoid them), you might start with @cite{Goldberg, What every computer -scientist should know about floating-point numbers, Computing Surveys -?}. +avoid them), you might start with @cite{David Goldberg, What Every +Computer Scientist Should Know About Floating-Point Arithmetic, ACM +Computing Surveys 23(1):5@minus{}48, March 1991}. doc-f+ doc-f- @@ -449,6 +468,7 @@ doc-fexpm1 doc-fln doc-flnp1 doc-flog +doc-falog doc-fsin doc-fcos doc-fsincos @@ -467,7 +487,7 @@ doc-fatanh @node Stack Manipulation, Memory access, Arithmetic, Words @section Stack Manipulation -gforth has a data stack (aka parameter stack) for characters, cells, +Gforth has a data stack (aka parameter stack) for characters, cells, addresses, and double cells, a floating point stack for floating point numbers, a return stack for storing the return addresses of colon definitions and other data, and a locals stack for storing local @@ -593,7 +613,7 @@ must only occur at specific addresses; e accessed at addresses divisible by 4. Even if a machine allows unaligned accesses, it can usually perform aligned accesses faster. -For the performance-concious: alignment operations are usually only +For the performance-conscious: alignment operations are usually only necessary during the definition of a data structure, not during the (more frequent) accesses to it. @@ -603,9 +623,12 @@ char-aligned have no use in the standard created. The standard guarantees that addresses returned by @code{CREATE}d words -are cell-aligned; in addition, gforth guarantees that these addresses +are cell-aligned; in addition, Gforth guarantees that these addresses are aligned for all purposes. +Note that the standard defines a word @code{char}, which has nothing to +do with address arithmetic. + doc-chars doc-char+ doc-cells @@ -624,6 +647,10 @@ doc-dfloats doc-dfloat+ doc-dfalign doc-dfaligned +doc-maxalign +doc-maxaligned +doc-cfalign +doc-cfaligned doc-address-unit-bits @node Memory block access, , Address arithmetic, Memory access @@ -782,13 +809,27 @@ There are several variations on the coun @code{LEAVE} leaves the innermost counted loop immediately. +If @var{start} is greater than @var{limit}, a @code{?DO} loop is entered +(and @code{LOOP} iterates until they become equal by wrap-around +arithmetic). This behaviour is usually not what you want. Therefore, +Gforth offers @code{+DO} and @code{U+DO} (as replacements for +@code{?DO}), which do not enter the loop if @var{start} is greater than +@var{limit}; @code{+DO} is for signed loop parameters, @code{U+DO} for +unsigned loop parameters. These words can be implemented easily on +standard systems, so using them does not make your programs hard to +port; e.g.: +@example +: +DO ( compile-time: -- do-sys; run-time: n1 n2 -- ) + POSTPONE over POSTPONE min POSTPONE ?DO ; immediate +@end example + @code{LOOP} can be replaced with @code{@var{n} +LOOP}; this updates the index by @var{n} instead of by 1. The loop is terminated when the border between @var{limit-1} and @var{limit} is crossed. E.g.: -@code{4 0 ?DO i . 2 +LOOP} prints @code{0 2} +@code{4 0 +DO i . 2 +LOOP} prints @code{0 2} -@code{4 1 ?DO i . 2 +LOOP} prints @code{1 3} +@code{4 1 +DO i . 2 +LOOP} prints @code{1 3} The behaviour of @code{@var{n} +LOOP} is peculiar when @var{n} is negative: @@ -796,23 +837,34 @@ The behaviour of @code{@var{n} +LOOP} is @code{ 0 0 ?DO i . -1 +LOOP} prints nothing -Therefore we recommend avoiding using @code{@var{n} +LOOP} with negative -@var{n}. One alternative is @code{@var{n} S+LOOP}, where the negative -case behaves symmetrical to the positive case: +Therefore we recommend avoiding @code{@var{n} +LOOP} with negative +@var{n}. One alternative is @code{@var{u} -LOOP}, which reduces the +index by @var{u} each iteration. The loop is terminated when the border +between @var{limit+1} and @var{limit} is crossed. Gforth also provides +@code{-DO} and @code{U-DO} for down-counting loops. E.g.: -@code{-2 0 ?DO i . -1 +LOOP} prints @code{0 -1} +@code{-2 0 -DO i . 1 -LOOP} prints @code{0 -1} -@code{-1 0 ?DO i . -1 +LOOP} prints @code{0} +@code{-1 0 -DO i . 1 -LOOP} prints @code{0} -@code{ 0 0 ?DO i . -1 +LOOP} prints nothing +@code{ 0 0 -DO i . 1 -LOOP} prints nothing + +Another alternative is @code{@var{n} S+LOOP}, where the negative +case behaves symmetrical to the positive case: + +@code{-2 0 -DO i . -1 S+LOOP} prints @code{0 -1} -The loop is terminated when the border between @var{limit@minus{}sgn(n)} and -@var{limit} is crossed. However, @code{S+LOOP} is not part of the ANS -Forth standard. - -@code{?DO} can be replaced by @code{DO}. @code{DO} enters the loop even -when the start and the limit value are equal. We do not recommend using -@code{DO}. It will just give you maintenance troubles. +The loop is terminated when the border between @var{limit@minus{}sgn(n)} +and @var{limit} is crossed. Unfortunately, neither @code{-LOOP} nor +@code{S+LOOP} are part of the ANS Forth standard, and they are not easy +to implement using standard words. If you want to write standard +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{EXIT}. @code{UNLOOP} removes the loop control parameters from the @@ -826,7 +878,7 @@ FOR NEXT @end example This is the preferred loop of native code compiler writers who are too -lazy to optimize @code{?DO} loops properly. In GNU Forth, this loop +lazy to optimize @code{?DO} loops properly. In Gforth, this loop iterates @var{n+1} times; @code{i} produces values starting with @var{n} and ending with 0. Other Forth systems may behave differently, even if they support @code{FOR} loops. @@ -837,7 +889,7 @@ they support @code{FOR} loops. ANS Forth permits and supports using control structures in a non-nested way. Information about incomplete control structures is stored on the control-flow stack. This stack may be implemented on the Forth data -stack, and this is what we have done in gforth. +stack, and this is what we have done in Gforth. An @i{orig} entry represents an unresolved forward branch, a @i{dest} entry represents a backward branch target. A few words are the basis for @@ -853,7 +905,7 @@ doc-again doc-cs-pick doc-cs-roll -On many systems control-flow stack items take one word, in gforth they +On many systems control-flow stack items take one word, in Gforth they currently take three (this may change in the future). Therefore it is a really good idea to manipulate the control flow stack with @code{cs-pick} and @code{cs-roll}, not with data stack manipulation @@ -868,23 +920,28 @@ doc-repeat Counted loop words constitute a separate group of words: doc-?do +doc-+do +doc-u+do +doc--do +doc-u-do doc-do doc-for doc-loop doc-s+loop doc-+loop +doc--loop doc-next doc-leave doc-?leave doc-unloop -doc-undo +doc-done The standard does not allow using @code{cs-pick} and @code{cs-roll} on @i{do-sys}. Our system allows it, but it's your job to ensure that for every @code{?DO} etc. there is exactly one @code{UNLOOP} on any path through the definition (@code{LOOP} etc. compile an @code{UNLOOP} on the fall-through path). Also, you have to ensure that all @code{LEAVE}s are -resolved (by using one of the loop-ending words or @code{UNDO}). +resolved (by using one of the loop-ending words or @code{DONE}). Another group of control structure words are @@ -943,7 +1000,8 @@ necessary to define them. @subsection Calls and returns A definition can be called simply be writing the name of the -definition. When the end of the definition is reached, it returns. An earlier return can be forced using +definition. When the end of the definition is reached, it returns. An +earlier return can be forced using doc-exit @@ -969,12 +1027,12 @@ locals wordset, but also our own, more p implemented the ANS Forth locals wordset through our locals wordset). @menu -* gforth locals:: +* Gforth locals:: * ANS Forth locals:: @end menu -@node gforth locals, ANS Forth locals, Locals, Locals -@subsection gforth locals +@node Gforth locals, ANS Forth locals, Locals, Locals +@subsection Gforth locals Locals can be defined with @@ -1017,7 +1075,7 @@ The name of the local may be preceded by Ar Bi f* Ai Br f* f+ ; @end example -GNU Forth currently supports cells (@code{W:}, @code{W^}), doubles +Gforth currently supports cells (@code{W:}, @code{W^}), doubles (@code{D:}, @code{D^}), floats (@code{F:}, @code{F^}) and characters (@code{C:}, @code{C^}) in two flavours: a value-flavoured local (defined with @code{W:}, @code{D:} etc.) produces its value and can be changed @@ -1037,16 +1095,17 @@ locals are initialized with values from Currently there is no way to define locals with user-defined data structures, but we are working on it. -GNU Forth allows defining locals everywhere in a colon definition. This poses the following questions: +Gforth allows defining locals everywhere in a colon definition. This +poses the following questions: @menu * Where are locals visible by name?:: -* How long do locals live? :: +* How long do locals live?:: * Programming Style:: * Implementation:: @end menu -@node Where are locals visible by name?, How long do locals live?, gforth locals, gforth locals +@node Where are locals visible by name?, How long do locals live?, Gforth locals, Gforth locals @subsubsection Where are locals visible by name? Basically, the answer is that locals are visible where you would expect @@ -1168,9 +1227,10 @@ If the @code{BEGIN} is not reachable fro @code{AHEAD} or @code{EXIT}), the compiler cannot even make an optimistic guess, as the locals visible after the @code{BEGIN} may be defined later. Therefore, the compiler assumes that no locals are -visible after the @code{BEGIN}. However, the useer can use +visible after the @code{BEGIN}. However, the user can use @code{ASSUME-LIVE} to make the compiler assume that the same locals are -visible at the BEGIN as at the point where the item was created. +visible at the BEGIN as at the point where the top control-flow stack +item was created. doc-assume-live @@ -1204,7 +1264,7 @@ WHILE REPEAT @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? The right answer for the lifetime question would be: A local lives at @@ -1218,7 +1278,7 @@ languages (e.g., C): The local lives onl afterwards its address is invalid (and programs that access it 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 The freedom to define locals anywhere has the potential to change @@ -1232,7 +1292,7 @@ write the items in the order you want. This seems a little far-fetched and eliminating stack manipulations is unlikely to become a conscious programming objective. Still, the number of stack manipulations will be reduced dramatically if local variables -are used liberally (e.g., compare @code{max} in @ref{gforth locals} with +are used liberally (e.g., compare @code{max} in @ref{Gforth locals} with a traditional implementation of @code{max}). This shows one potential benefit of locals: making Forth programs more @@ -1287,10 +1347,10 @@ are initialized with the right value for Here it is clear from the start that @code{s1} has a different value in every loop iteration. -@node Implementation, , Programming Style, gforth locals +@node Implementation, , Programming Style, Gforth locals @subsubsection Implementation -GNU Forth uses an extra locals stack. The most compelling reason for +Gforth uses an extra locals stack. The most compelling reason for this is that the return stack is not float-aligned; using an extra stack also eliminates the problems and restrictions of using the return stack as locals stack. Like the other stacks, the locals stack grows toward @@ -1311,8 +1371,8 @@ efficiency reasons, e.g., @code{@@local0 compile the right specialized version, or the general version, as appropriate: -doc-compile-@@local -doc-compile-f@@local +doc-compile-@local +doc-compile-f@local doc-compile-lp+! Combinations of conditional branches and @code{lp+!#} like @@ -1325,7 +1385,7 @@ area and @code{@}} switches it back and initializing code. @code{W:} etc.@ are normal defining words. This special area is cleared at the start of every colon definition. -A special feature of GNU Forths dictionary is used to implement the +A special feature of Gforth's dictionary is used to implement the definition of locals without type specifiers: every wordlist (aka vocabulary) has its own methods for searching etc. (@pxref{Wordlists}). For the present purpose we defined a wordlist @@ -1415,12 +1475,12 @@ this may lead to increased space needs f 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 The ANS Forth locals wordset does not define a syntax for locals, but words that make it possible to define various syntaxes. One of the -possible syntaxes is a subset of the syntax we used in the gforth locals +possible syntaxes is a subset of the syntax we used in the Gforth locals wordset, i.e.: @example @@ -1436,13 +1496,13 @@ restrictions are: @itemize @bullet @item -Locals can only be cell-sized values (no type specifers are allowed). +Locals can only be cell-sized values (no type specifiers are allowed). @item Locals can be defined only outside control structures. @item Locals can interfere with explicit usage of the return stack. For the exact (and long) rules, see the standard. If you don't use return stack -accessing words in a definition using locals, you will we all right. The +accessing words in a definition using locals, you will be all right. The purpose of this rule is to make locals implementation on the return stack easier. @item @@ -1453,7 +1513,7 @@ Locals defined in this way behave like @ (@xref{Values}). I.e., they are initialized from the stack. Using their name produces their value. Their value can be changed using @code{TO}. -Since this syntax is supported by gforth directly, you need not do +Since this syntax is supported by Gforth directly, you need not do anything to use it. If you want to port a program using this syntax to another ANS Forth system, use @file{anslocal.fs} to implement the syntax on the other system. @@ -1468,7 +1528,7 @@ doc-(local) The ANS Forth locals extension wordset defines a syntax, but it is so awful that we strongly recommend not to use it. We have implemented this -syntax to make porting to gforth easy, but do not document it here. The +syntax to make porting to Gforth easy, but do not document it here. The problem with this syntax is that the locals are defined in an order reversed with respect to the standard stack comment notation, making programs harder to read, and easier to misread and miswrite. The only @@ -1478,6 +1538,10 @@ locals wordset. @node Defining Words, Wordlists, Locals, Words @section Defining Words +@menu +* Values:: +@end menu + @node Values, , Defining Words, Defining Words @subsection Values @@ -1493,10 +1557,15 @@ locals wordset. @node Other I/O, Programming Tools, Blocks, Words @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 -@node +@menu +* Debugging:: Simple and quick. +* Assertions:: Making your programs self-checking. +@end menu + +@node Debugging, Assertions, Programming Tools, Programming Tools @subsection Debugging The simple debugging aids provided in @file{debugging.fs} @@ -1516,7 +1585,9 @@ query-replace them with nothing). The de @code{printdebugdata} and @code{printdebugline} control the output of @code{~~}. The default source location output format works well with Emacs' compilation mode, so you can step through the program at the -source level using @kbd{C-x `}. +source level using @kbd{C-x `} (the advantage over a stepping debugger +is that you can step in any direction and you know where the crash has +happened or where the strange data has occurred). Note that the default actions clobber the contents of the pictured numeric output string, so you should not use @code{~~}, e.g., between @@ -1526,14 +1597,106 @@ doc-~~ doc-printdebugdata doc-printdebugline -@node +@node Assertions, , Debugging, Programming Tools @subsection Assertions -@node Threading Words, , Programming Tools, Words +It is a good idea to make your programs self-checking, in particular, if +you use an assumption (e.g., that a certain field of a data structure is +never zero) that may become wrong during maintenance. Gforth supports +assertions for this purpose. They are used like this: + +@example +assert( @var{flag} ) +@end example + +The code between @code{assert(} and @code{)} should compute a flag, that +should be true if everything is alright and false otherwise. It should +not change anything else on the stack. The overall stack effect of the +assertion is @code{( -- )}. E.g. + +@example +assert( 1 1 + 2 = ) \ what we learn in school +assert( dup 0<> ) \ assert that the top of stack is not zero +assert( false ) \ this code should not be reached +@end example + +The need for assertions is different at different times. During +debugging, we want more checking, in production we sometimes care more +for speed. Therefore, assertions can be turned off, i.e., the assertion +becomes a comment. Depending on the importance of an assertion and the +time it takes to check it, you may want to turn off some assertions and +keep others turned on. Gforth provides several levels of assertions for +this purpose: + +doc-assert0( +doc-assert1( +doc-assert2( +doc-assert3( +doc-assert( +doc-) + +@code{Assert(} is the same as @code{assert1(}. The variable +@code{assert-level} specifies the highest assertions that are turned +on. I.e., at the default @code{assert-level} of one, @code{assert0(} and +@code{assert1(} assertions perform checking, while @code{assert2(} and +@code{assert3(} assertions are treated as comments. + +Note that the @code{assert-level} is evaluated at compile-time, not at +run-time. I.e., you cannot turn assertions on or off at run-time, you +have to set the @code{assert-level} appropriately before compiling a +piece of code. You can compile several pieces of code at several +@code{assert-level}s (e.g., a trusted library at level 1 and newly +written code at level 3). + +doc-assert-level + +If an assertion fails, a message compatible with Emacs' compilation mode +is produced and the execution is aborted (currently with @code{ABORT"}. +If there is interest, we will introduce a special throw code. But if you +intend to @code{catch} a specific condition, using @code{throw} is +probably more appropriate than an assertion). + +@node Assembler and Code words, Threading Words, Programming Tools, Words +@section Assembler and Code words + +Gforth provides some words for defining primitives (words written in +machine code), and for defining the the machine-code equivalent of +@code{DOES>}-based defining words. However, the machine-independent +nature of Gforth poses a few problems: First of all. Gforth runs on +several architectures, so it can provide no standard assembler. What's +worse is that the register allocation not only depends on the processor, +but also on the gcc version and options used. + +The words Gforth offers encapsulate some system dependences (e.g., the +header structure), so a system-independent assembler may be used in +Gforth. If you do not have an assembler, you can compile machine code +directly with @code{,} and @code{c,}. + +doc-assembler +doc-code +doc-end-code +doc-;code +doc-flush-icache + +If @code{flush-icache} does not work correctly, @code{code} words +etc. will not work (reliably), either. + +These words are rarely used. Therefore they reside in @code{code.fs}, +which is usually not loaded (except @code{flush-icache}, which is always +present). You can load it with @code{require code.fs}. + +Another option for implementing normal and defining words efficiently +is: adding the wanted functionality to the source of Gforth. For normal +words you just have to edit @file{primitives}, defining words (for fast +defined words) probably require changes in @file{engine.c}, +@file{kernal.fs}, @file{prims2x.fs}, and possibly @file{cross.fs}. + + +@node Threading Words, , Assembler and Code words, Words @section Threading Words These words provide access to code addresses and other threading stuff -in gforth (and, possibly, other interpretive Forths). It more or less +in Gforth (and, possibly, other interpretive Forths). It more or less abstracts away the differences between direct and indirect threading (and, for direct threading, the machine dependences). However, at present this wordset is still inclomplete. It is also pretty low-level; @@ -1547,25 +1710,1060 @@ doc-does-code! doc-does-handler! doc-/does-handler +The code addresses produced by various defining words are produced by +the following words: + +doc-docol: +doc-docon: +doc-dovar: +doc-douser: +doc-dodefer: +doc-dofield: + +Currently there is no installation-independent way for recogizing words +defined by a @code{CREATE}...@code{DOES>} word; however, once you know +that a word is defined by a @code{CREATE}...@code{DOES>} word, you can +use @code{>DOES-CODE}. + @node ANS conformance, Model, Words, Top @chapter ANS conformance -@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 -@node Emacs and GForth, Internals, Model, Top -@chapter Emacs and GForth +@node Emacs and Gforth, Internals, Model, Top +@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 improvements are a better (but still not perfect) handling of indentation. I have also added comment paragraph filling (@kbd{M-q}), -commenting (@kbd{C-x \}) and uncommenting (@kbd{C-x |}) regions and -removing debugging tracers (@kbd{C-x ~}). I left the stuff I do not use -alone, even though some of it only makes sense for TILE. To get a -description of these features, enter Forth mode and type @kbd{C-h m}. +commenting (@kbd{C-x \}) and uncommenting (@kbd{C-u C-x \}) regions and +removing debugging tracers (@kbd{C-x ~}, @pxref{Debugging}). I left the +stuff I do not use alone, even though some of it only makes sense for +TILE. To get a description of these features, enter Forth mode and type +@kbd{C-h m}. -In addition, GForth supports Emacs quite well: The source code locations +In addition, Gforth supports Emacs quite well: The source code locations given in error messages, debugging output (from @code{~~}) and failed assertion messages are in the right format for Emacs' compilation mode (@pxref{Compilation, , Running Compilations under Emacs, emacs, Emacs @@ -1577,7 +2775,7 @@ Also, if you @code{include} @file{etags. (@pxref{Tags, , Tags Tables, emacs, Emacs Manual}) will be produced that contains the definitions of all words defined afterwards. You can then find the source for a word using @kbd{M-.}. Note that emacs can use -several tags files at the same time (e.g., one for the gforth sources +several tags files at the same time (e.g., one for the Gforth sources and one for your program). To get all these benefits, add the following lines to your @file{.emacs} @@ -1588,17 +2786,18 @@ file: (setq auto-mode-alist (cons '("\\.fs\\'" . forth-mode) auto-mode-alist)) @end example -@node Internals, Bugs, Emacs and GForth, Top +@node Internals, Bugs, Emacs and Gforth, Top @chapter Internals -Reading this section is not necessary for programming with gforth. It -should be helpful for finding your way in the gforth sources. +Reading this section is not necessary for programming with Gforth. It +should be helpful for finding your way in the Gforth sources. @menu * Portability:: * Threading:: * Primitives:: * System Architecture:: +* Performance:: @end menu @node Portability, Threading, Internals, Internals @@ -1630,9 +2829,7 @@ Double-Word Integers, gcc.info, GNU C Ma double numbers. GNU C is available for free on all important (and many unimportant) UNIX machines, VMS, 80386s running MS-DOS, the Amiga, and the Atari ST, so a Forth written in GNU C can run on all these -machines@footnote{Due to Apple's look-and-feel lawsuit it is not -available on the Mac (@pxref{Boycott, , Protect Your Freedom--Fight -``Look And Feel'', gcc.info, GNU C Manual}).}. +machines. Writing in a portable language has the reputation of producing code that is slower than assembly. For our Forth engine we repeatedly looked at @@ -1923,7 +3120,7 @@ To see what assembly code is produced fo with your compiler and your flag settings, type @code{make engine.s} and look at the resulting file @file{engine.s}. -@node System Architecture, , Primitives, Internals +@node System Architecture, Performance, Primitives, Internals @section System Architecture Our Forth system consists not only of primitives, but also of @@ -1946,7 +3143,7 @@ possible, because we do not want to dist same image file, and to make it easy for the users to use their image files on many machines. We currently need to create a different image file for machines with different cell sizes and different byte order -(little- or big-endian)@footnote{We consider adding information to the +(little- or big-endian)@footnote{We are considering adding information to the image file that enables the loader to change the byte order.}. Forth code that is going to end up in a portable image file has to @@ -1966,18 +3163,130 @@ at run-time. The loader also has to repl primitive calls with the appropriate code-field addresses (or code addresses in the case of direct threading). +@node Performance, , System Architecture, Internals +@section Performance + +On RISCs the Gforth engine is very close to optimal; i.e., it is usually +impossible to write a significantly faster engine. + +On register-starved machines like the 386 architecture processors +improvements are possible, because @code{gcc} does not utilize the +registers as well as a human, even with explicit register declarations; +e.g., Bernd Beuster wrote a Forth system fragment in assembly language +and hand-tuned it for the 486; this system is 1.19 times faster on the +Sieve benchmark on a 486DX2/66 than Gforth compiled with +@code{gcc-2.6.3} with @code{-DFORCE_REG}. + +However, this potential advantage of assembly language implementations +is not necessarily realized in complete Forth systems: We compared +Gforth (compiled with @code{gcc-2.6.3} and @code{-DFORCE_REG}) with +Win32Forth 1.2093 and LMI's NT Forth (Beta, May 1994), two systems +written in assembly, and with two systems written in C: PFE-0.9.11 +(compiled with @code{gcc-2.6.3} with the default configuration for +Linux: @code{-O2 -fomit-frame-pointer -DUSE_REGS}) and ThisForth Beta +(compiled with gcc-2.6.3 -O3 -fomit-frame-pointer). We benchmarked +Gforth, PFE and ThisForth on a 486DX2/66 under Linux. Kenneth O'Heskin +kindly provided the results for Win32Forth and NT Forth on a 486DX2/66 +with similar memory performance under Windows NT. + +We used four small benchmarks: the ubiquitous Sieve; bubble-sorting and +matrix multiplication come from the Stanford integer benchmarks and have +been translated into Forth by Martin Fraeman; we used the versions +included in the TILE Forth package; and a recursive Fibonacci number +computation for 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 @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 @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 @chapter Word Index +This index is as incomplete as the manual. Each word is listed with +stack effect and wordset. + +@printindex fn + @node Node Index, , Word Index, Top @chapter Node Index +This index is even less complete than the manual. + @contents @bye