This is gforth.info, produced by makeinfo version 4.0 from gforth.texi.

INFO-DIR-SECTION GNU programming tools
START-INFO-DIR-ENTRY
* Gforth: (gforth).             A fast interpreter for the Forth language.
END-INFO-DIR-ENTRY

   This file documents Gforth 0.5.0

   Copyright (C) 1995-2000 Free Software Foundation, Inc.

   Permission is granted to make and distribute verbatim copies of
this manual provided the copyright notice and this permission notice
 are preserved on all copies.

   Permission is granted to copy and distribute modified versions of
this      manual under the conditions for verbatim copying, provided
also that the      sections entitled "Distribution" and "General Public
License" are      included exactly as in the original, and provided
that the entire      resulting derived work is distributed under the
terms of a permission      notice identical to this one.

   Permission is granted to copy and distribute translations of this
manual      into another language, under the above conditions for
modified versions,      except that the sections entitled
"Distribution" and "General Public      License" may be included in a
translation approved by the author instead      of in the original
English.


File: gforth.info,  Node: MIPS assembler,  Next: Other assemblers,  Prev: Alpha Assembler,  Up: Assembler and Code Words

MIPS assembler
--------------

   The MIPS assembler was originally written by Christian Pirker.

   Currently the assembler and disassembler only cover the MIPS-I
architecture (R3000), and don't support FP instructions.

   The register names `$a0'-`$a3' are not available to avoid shadowing
hex numbers.

   Because there is no way to distinguish registers from immediate
values, you have to explicitly use the immediate forms of instructions,
i.e., `addiu,', not just `addu,' (`as' does this implicitly).

   If the architecture manual specifies several formats for the
instruction (e.g., for `jalr,'), you usually have to use the one with
more arguments (i.e., two for `jalr,').  When in doubt, see
`arch/mips/testasm.fs' for an example of correct use.

   Branches and jumps in the MIPS architecture have a delay slot.  You
have to fill it yourself (the simplest way is to use `nop,'), the
assembler does not do it for you (unlike `as').  Even `if,', `ahead,',
`until,', `again,', `while,', `else,' and `repeat,' need a delay slot.
Since `begin,' and `then,' just specify branch targets, they are not
affected.

   Note that you must not put branches, jumps, or `li,' into the delay
slot: `li,' may expand to several instructions, and control flow
instructions may not be put into the branch delay slot in any case.

   For branches the argument specifying the target is a relative
address; You have to add the address of the delay slot to get the
absolute address.

   The MIPS architecture also has load delay slots and restrictions on
using `mfhi,' and `mflo,'; you have to order the instructions yourself
to satisfy these restrictions, the assembler does not do it for you.

   You can specify the conditions for `if,' etc. by taking a
conditional branch and leaving away the `b' at the start and the `,' at
the end.  E.g.,

     4 5 eq if,
       ... \ do something if $4 equals $5
     then,


File: gforth.info,  Node: Other assemblers,  Prev: MIPS assembler,  Up: Assembler and Code Words

Other assemblers
----------------

   If you want to contribute another assembler/disassembler, please
contact us (<bug-gforth@gnu.org>) to check if we have such an assembler
already.  If you are writing them from scratch, please use a similar
syntax style as the one we use (i.e., postfix, commas at the end of the
instruction names, *note Common Assembler::); make the output of the
disassembler be valid input for the assembler, and keep the style
similar to the style we used.

   Hints on implementation: The most important part is to have a good
test suite that contains all instructions.  Once you have that, the
rest is easy.  For actual coding you can take a look at
`arch/mips/disasm.fs' to get some ideas on how to use data for both the
assembler and disassembler, avoiding redundancy and some potential
bugs.  You can also look at that file (and *note Advanced does> usage
example::) to get ideas how to factor a disassembler.

   Start with the disassembler, because it's easier to reuse data from
the disassembler for the assembler than the other way round.

   For the assembler, take a look at `arch/alpha/asm.fs', which shows
how simple it can be.


File: gforth.info,  Node: Threading Words,  Next: Passing Commands to the OS,  Prev: Assembler and Code Words,  Up: Words

Threading Words
===============

   These words provide access to code addresses and other threading
stuff in Gforth (and, possibly, other interpretive Forths). It more or
less abstracts away the differences between direct and indirect
threading (and, for direct threading, the machine dependences).
However, at present this wordset is still incomplete. It is also pretty
low-level; some day it will hopefully be made unnecessary by an
internals wordset that abstracts implementation details away completely.

   The terminology used here stems from indirect threaded Forth
systems; in such a system, the XT of a word is represented by the CFA
(code field address) of a word; the CFA points to a cell that contains
the code address.  The code address is the address of some machine code
that performs the run-time action of invoking the word (e.g., the
`dovar:' routine pushes the address of the body of the word (a
variable) on the stack ).

   In an indirect threaded Forth, you can get the code address of name
with `' name @'; in Gforth you can get it with `' name >code-address',
independent of the threading method.

`threading-method'       - n        gforth       ``threading-method''
   0 if the engine is direct threaded. Note that this may change during
the lifetime of an image.

`>code-address'       xt - c-addr        gforth       ``to-code-address''
   c-addr is the code address of the word xt.

`code-address!'       c-addr xt -        gforth       ``code-address-store''
   Create a code field with code address c-addr at xt.

   For a word defined with `DOES>', the code address usually points to
a jump instruction (the "does-handler") that jumps to the dodoes
routine (in Gforth on some platforms, it can also point to the dodoes
routine itself).  What you are typically interested in, though, is
whether a word is a `DOES>'-defined word, and what Forth code it
executes; `>does-code' tells you that.

`>does-code'       xt - a-addr        gforth       ``to-does-code''
   If xt is the execution token of a child of a `DOES>' word, a-addr is
the start of the Forth code after the `DOES>'; Otherwise a-addr is 0.

   To create a `DOES>'-defined word with the following basic words, you
have to set up a `DOES>'-handler with `does-handler!'; `/does-handler'
aus behind you have to place your executable Forth code.  Finally you
have to create a word and modify its behaviour with `does-handler!'.

`does-code!'       a-addr xt -        gforth       ``does-code-store''
   Create a code field at xt for a child of a `DOES>'-word; a-addr is
the start of the Forth code after `DOES>'.

`does-handler!'       a-addr -        gforth       ``does-handler-store''
   Create a `DOES>'-handler at address a-addr. Normally, a-addr points
just behind a `DOES>'.

`/does-handler'       - n        gforth       ``slash-does-handler''
   The size of a `DOES>'-handler (includes possible padding).

   The code addresses produced by various defining words are produced by
the following words:

`docol:'       - addr         gforth       ``docol:''
   The code address of a colon definition.

`docon:'       - addr         gforth       ``docon:''
   The code address of a `CONSTANT'.

`dovar:'       - addr         gforth       ``dovar:''
   The code address of a `CREATE'd word.

`douser:'       - addr         gforth       ``douser:''
   The code address of a `USER' variable.

`dodefer:'       - addr         gforth       ``dodefer:''
   The code address of a `defer'ed word.

`dofield:'       - addr         gforth       ``dofield:''
   The code address of a `field'.


File: gforth.info,  Node: Passing Commands to the OS,  Next: Keeping track of Time,  Prev: Threading Words,  Up: Words

Passing Commands to the Operating System
========================================

   Gforth allows you to pass an arbitrary string to the host operating
system shell (if such a thing exists) for execution.

`sh'       "..." -         gforth       ``sh''
   Parse a string and use `system' to pass it to the host operating
system for execution in a sub-shell.

`system'       c-addr u -         gforth       ``system''
   Pass the string specified by C-ADDR U to the host operating system
for execution in a sub-shell.

`$?'       - n         gforth       ``dollar-question''
   `Value' - the exit status returned by the most recently executed
`system' command.

`getenv'       c-addr1 u1 - c-addr2 u2        gforth       ``getenv''
   The string c-addr1 u1 specifies an environment variable. The string
c-addr2 u2 is the host operating system's expansion of that environment
variable. If the environment variable does not exist, c-addr2 u2
specifies a string 0 characters in length.


File: gforth.info,  Node: Keeping track of Time,  Next: Miscellaneous Words,  Prev: Passing Commands to the OS,  Up: Words

Keeping track of Time
=====================

`ms'       n -        facility-ext       ``ms''
   Wait at least n milli-second.

`time&date'       - nsec nmin nhour nday nmonth nyear        facility-ext       ``time-and-date''
   Report the current time of day. Seconds, minutes and hours are
numbered from 0.  Months are numbered from 1.

`utime'       - dtime        gforth       ``utime''
   Report the current time in microseconds since some epoch.

`cputime'       - duser dsystem        gforth       ``cputime''
   duser and dsystem are the respective user- and system-level CPU
times used since the start of the Forth system (excluding child
processes), in microseconds (the granularity may be much larger,
however).  On platforms without the getrusage call, it reports elapsed
time (since some epoch) for duser and 0 for dsystem.


File: gforth.info,  Node: Miscellaneous Words,  Prev: Keeping track of Time,  Up: Words

Miscellaneous Words
===================

   These section lists the ANS Forth words that are not documented
elsewhere in this manual. Ultimately, they all need proper homes.

`quit'       ?? - ??         core       ``quit''
   Empty the return stack, make the user input device the input source,
enter interpret state and start the text interpreter.

   The following ANS Forth words are not currently supported by Gforth
(*note ANS conformance::):

   `EDITOR' `EMIT?' `FORGET'


File: gforth.info,  Node: Error messages,  Next: Tools,  Prev: Words,  Up: Top

Error messages
**************

   A typical Gforth error message looks like this:

     in file included from \evaluated string/:-1
     in file included from ./yyy.fs:1
     ./xxx.fs:4: Invalid memory address
     bar
     ^^^
     Backtrace:
     $400E664C @
     $400E6664 foo

   The message identifying the error is `Invalid memory address'.  The
error happened when text-interpreting line 4 of the file `./xxx.fs'.
This line is given (it contains `bar'), and the word on the line where
the error happened, is pointed out (with `^^^').

   The file containing the error was included in line 1 of `./yyy.fs',
and `yyy.fs' was included from a non-file (in this case, by giving
`yyy.fs' as command-line parameter to Gforth).

   At the end of the error message you find a return stack dump that
can be interpreted as a backtrace (possibly empty). On top you find the
top of the return stack when the `throw' happened, and at the bottom you
find the return stack entry just above the return stack of the topmost
text interpreter.

   To the right of most return stack entries you see a guess for the
word that pushed that return stack entry as its return address. This
gives a backtrace. In our case we see that `bar' called `foo', and
`foo' called `@' (and `@' had an _Invalid memory address_ exception).

   Note that the backtrace is not perfect: We don't know which return
stack entries are return addresses (so we may get false positives); and
in some cases (e.g., for `abort"') we cannot determine from the return
address the word that pushed the return address, so for some return
addresses you see no names in the return stack dump.

   The return stack dump represents the return stack at the time when a
specific `throw' was executed.  In programs that make use of `catch',
it is not necessarily clear which `throw' should be used for the return
stack dump (e.g., consider one `throw' that indicates an error, which
is caught, and during recovery another error happens; which `throw'
should be used for the stack dump?).  Gforth presents the return stack
dump for the first `throw' after the last executed (not returned-to)
`catch'; this works well in the usual case.

   `Gforth' is able to do a return stack dump for throws generated from
primitives (e.g., invalid memory address, stack empty etc.);
`gforth-fast' is only able to do a return stack dump from a directly
called `throw' (including `abort' etc.).  This is the only difference
(apart from a speed factor of between 1.15 (K6-2) and 2 (21264))
between `gforth' and `gforth-fast'.  Given an exception caused by a
primitive in `gforth-fast', you will typically see no return stack dump
at all; however, if the exception is caught by `catch' (e.g., for
restoring some state), and then `throw'n again, the return stack dump
will be for the first such `throw'.


File: gforth.info,  Node: Tools,  Next: ANS conformance,  Prev: Error messages,  Up: Top

Tools
*****

* Menu:

* ANS Report::                  Report the words used, sorted by wordset.

   See also *Note Emacs and Gforth::.


File: gforth.info,  Node: ANS Report,  Prev: Tools,  Up: Tools

`ans-report.fs': Report the words used, sorted by wordset
=========================================================

   If you want to label a Forth program as ANS Forth Program, you must
document which wordsets the program uses; for extension wordsets, it is
helpful to list the words the program requires from these wordsets
(because Forth systems are allowed to provide only some words of them).

   The `ans-report.fs' tool makes it easy for you to determine which
words from which wordset and which non-ANS words your application uses.
You simply have to include `ans-report.fs' before loading the program
you want to check. After loading your program, you can get the report
with `print-ans-report'. A typical use is to run this as batch job like
this:
     gforth ans-report.fs myprog.fs -e "print-ans-report bye"

   The output looks like this (for `compat/control.fs'):
     The program uses the following words
     from CORE :
     : POSTPONE THEN ; immediate ?dup IF 0=
     from BLOCK-EXT :
     \
     from FILE :
     (

Caveats
-------

   Note that `ans-report.fs' just checks which words are used, not
whether they are used in an ANS Forth conforming way!

   Some words are defined in several wordsets in the standard.
`ans-report.fs' reports them for only one of the wordsets, and not
necessarily the one you expect. It depends on usage which wordset is
the right one to specify. E.g., if you only use the compilation
semantics of `S"', it is a Core word; if you also use its
interpretation semantics, it is a File word.


File: gforth.info,  Node: ANS conformance,  Next: Standard vs Extensions,  Prev: Tools,  Up: Top

ANS conformance
***************

   To the best of our knowledge, Gforth is an

   ANS Forth System
   * providing the Core Extensions word set

   * providing the Block word set

   * providing the Block Extensions word set

   * providing the Double-Number word set

   * providing the Double-Number Extensions word set

   * providing the Exception word set

   * providing the Exception Extensions word set

   * providing the Facility word set

   * providing `EKEY', `EKEY>CHAR', `EKEY?', `MS' and `TIME&DATE' from
     the Facility Extensions word set

   * providing the File Access word set

   * providing the File Access Extensions word set

   * providing the Floating-Point word set

   * providing the Floating-Point Extensions word set

   * providing the Locals word set

   * providing the Locals Extensions word set

   * providing the Memory-Allocation word set

   * providing the Memory-Allocation Extensions word set (that one's
     easy)

   * providing the Programming-Tools word set

   * providing `;CODE', `AHEAD', `ASSEMBLER', `BYE', `CODE', `CS-PICK',
     `CS-ROLL', `STATE', `[ELSE]', `[IF]', `[THEN]' from the
     Programming-Tools Extensions word set

   * providing the Search-Order word set

   * providing the Search-Order Extensions word set

   * providing the String word set

   * providing the String Extensions word set (another easy one)

   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.

* 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::


File: gforth.info,  Node: The Core Words,  Next: The optional Block word set,  Prev: ANS conformance,  Up: ANS conformance

The Core Words
==============

* Menu:

* core-idef::                   Implementation Defined Options
* core-ambcond::                Ambiguous Conditions
* core-other::                  Other System Documentation


File: gforth.info,  Node: core-idef,  Next: core-ambcond,  Prev: The Core Words,  Up: The Core Words

Implementation Defined Options
------------------------------

(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 `-23
     THROW'.

`EMIT' and non-graphic characters:
     The character is output using the C library function (actually,
     macro) `putc'.

character editing of `ACCEPT' and `EXPECT':
     This is modeled on the GNU readline library (*note Command Line
     Editing: (readline)Readline Interaction.) with Emacs-like key
     bindings. `Tab' deviates a little by producing a full word
     completion every time you type it (instead of producing the common
     prefix of all completions). *Note Command-line editing::.

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).

Character-aligned address requirements:
     installation-dependent. Currently a character is represented by a C
     `unsigned char'; in the future we might switch to `wchar_t'
     (Comments on that requested).

character-set extensions and matching of names:
     Any character except the ASCII NUL character can be used in a
     name. Matching is case-insensitive (except in `TABLE's). The
     matching is performed using the C library function `strncasecmp',
     whose function is probably influenced by the locale. E.g., the `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 `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,
     `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.

conditions under which control characters match a space delimiter:
     If `WORD' is called with the space character as a delimiter, all
     white-space characters (as identified by the C macro `isspace()')
     are delimiters. `PARSE', on the other hand, treats space like other
     delimiters. `SWORD' treats space like `WORD', but behaves like
     `PARSE' otherwise. `Name', which is used by the outer interpreter
     (aka text interpreter) by default, treats all white-space
     characters as delimiters.

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
     `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: `defstart', `live-orig', `dead-orig', `dest',
     `do-dest', `scopestart'.

conversion of digits > 35
     The characters `[\]^_'' are the digits with the decimal value
     36-41. There is no way to input many of the larger digits.

display after input terminates in `ACCEPT' and `EXPECT':
     The cursor is moved to the end of the entered string. If the input
     is terminated using the `Return' key, a space is typed.

exception abort sequence of `ABORT"':
     The error string is stored into the variable `"error' and a `-2
     throw' is performed.

input line terminator:
     For interactive input, `C-m' (CR) and `C-j' (LF) terminate lines.
     One of these characters is typically produced when you type the
     `Enter' or `Return' key.

maximum size of a counted string:
     `s" /counted-string" environment? drop .'. Currently 255 characters
     on all platforms, but this may change.

maximum size of a parsed string:
     Given by the constant `/line'. Currently 255 characters.

maximum size of a definition name, in characters:
     31

maximum string length for `ENVIRONMENT?', in characters:
     31

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.

method of selecting the user output device:
     `EMIT' and `TYPE' output to the file-id stored in the value
     `outfile-id' (`stdout' by default). Gforth uses unbuffered output
     when the user output device is a terminal, otherwise the output is
     buffered.

methods of dictionary compilation:
     What are we expected to document here?

number of bits in one address unit:
     `s" address-units-bits" environment? drop .'. 8 in all current
     platforms.

number representation and arithmetic:
     Processor-dependent. Binary two's complement on all current
     platforms.

ranges for integer types:
     Installation-dependent. Make environmental queries for `MAX-N',
     `MAX-U', `MAX-D' and `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.

read-only data space regions:
     The whole Forth data space is writable.

size of buffer at `WORD':
     `PAD HERE - .'. 104 characters on 32-bit machines. The buffer is
     shared with the pictured numeric output string. If overwriting
     `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.

size of one cell in address units:
     `1 cells .'.

size of one character in address units:
     `1 chars .'. 1 on all current platforms.

size of the keyboard terminal buffer:
     Varies. You can determine the size at a specific time using `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 `-l'.

size of the pictured numeric output buffer:
     `PAD HERE - .'. 104 characters on 32-bit machines. The buffer is
     shared with `WORD'.

size of the scratch area returned by `PAD':
     The remainder of dictionary space. `unused pad here - - .'.

system case-sensitivity characteristics:
     Dictionary searches are case-insensitive (except in `TABLE's).
     However, as explained above under character-set extensions, the
     matching for non-ASCII characters is determined by the locale you
     are using. In the default `C' locale all non-ASCII characters are
     matched case-sensitively.

system prompt:
     ` ok' in interpret state, ` compiled' in compile state.

division rounding:
     installation dependent. `s" floored" environment? drop .'. We leave
     the choice to `gcc' (what to use for `/') and to you (whether to
     use `fm/mod', `sm/rem' or simply `/').

values of `STATE' when true:
     -1.

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 `-55 throw'
     (Floating-point unidentified fault) or `-10 throw' (divide by
     zero).

whether the current definition can be found after DOES>:
     No.


File: gforth.info,  Node: core-ambcond,  Next: core-other,  Prev: core-idef,  Up: The Core Words

Ambiguous conditions
--------------------

a name is neither a word nor a number:
     `-13 throw' (Undefined word).

a definition name exceeds the maximum length allowed:
     `-19 throw' (Word name too long)

addressing a region not inside the various data spaces of the forth system:
     The stacks, code space and header space are accessible. Machine
     code space is typically readable. Accessing other addresses gives
     results dependent on the operating system. On decent systems: `-9
     throw' (Invalid memory address).

argument type incompatible with parameter:
     This is usually not caught. Some words perform checks, e.g., the
     control flow words, and issue a `ABORT"' or `-12 THROW' (Argument
     type mismatch).

attempting to obtain the execution token of a word with undefined execution semantics:
     `-14 throw' (Interpreting a compile-only word). In some cases, you
     get an execution token for `compile-only-error' (which performs a
     `-14 throw' when executed).

dividing by zero:
     On some platforms, this produces a `-10 throw' (Division by zero);
     on other systems, this typically results in a `-55 throw'
     (Floating-point unidentified fault).

insufficient data stack or return stack space:
     Depending on the operating system, the installation, and the
     invocation of Gforth, this is either checked by the memory
     management hardware, or it is not checked. If it is checked, you
     typically get a `-3 throw' (Stack overflow), `-5 throw' (Return
     stack overflow), or `-9 throw' (Invalid memory address) (depending
     on the platform and how you achieved the overflow) as soon as the
     overflow happens. If it is not checked, overflows typically result
     in mysterious illegal memory accesses, producing `-9 throw'
     (Invalid memory address) or `-23 throw' (Address alignment
     exception); they might also destroy the internal data structure of
     `ALLOCATE' and friends, resulting in various errors in these words.

insufficient space for loop control parameters:
     Like other return stack overflows.

insufficient space in the dictionary:
     If you try to allot (either directly with `allot', or indirectly
     with `,', `create' etc.) more memory than available in the
     dictionary, you get a `-8 throw' (Dictionary overflow). If you try
     to access memory beyond the end of the dictionary, the results are
     similar to stack overflows.

interpreting a word with undefined interpretation semantics:
     For some words, we have defined interpretation semantics. For the
     others: `-14 throw' (Interpreting a compile-only word).

modifying the contents of the input buffer or a string literal:
     These are located in writable memory and can be modified.

overflow of the pictured numeric output string:
     `-17 throw' (Pictured numeric ouput string overflow).

parsed string overflow:
     `PARSE' cannot overflow. `WORD' does not check for overflow.

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 `-10 throw' (divide by
     zero) or `-55 throw' (floating point unidentified fault).
     `convert' and `>number' currently overflow silently.

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 `-4 throw' (Stack
     underflow) is performed. Apart from that, stacks may be checked or
     not, depending on operating system, installation, and invocation.
     If they are caught by a check, they typically result in `-4 throw'
     (Stack underflow), `-6 throw' (Return stack underflow) or `-9
     throw' (Invalid memory address), depending on the platform and
     which stack underflows and by how much. Note that even if the
     system uses checking (through the MMU), your program may have to
     underflow by a significant number of stack items to trigger the
     reaction (the reason for this is that the MMU, and therefore the
     checking, works with a page-size granularity).  If there is no
     checking, the symptoms resulting from an underflow are similar to
     those from an overflow.  Unbalanced return stack errors can result
     in a variety of symptoms, including `-9 throw' (Invalid memory
     address) and Illegal Instruction (typically `-260 throw').

unexpected end of the input buffer, resulting in an attempt to use a zero-length string as a name:
     `Create' and its descendants perform a `-16 throw' (Attempt to use
     zero-length string as a name). Words like `'' probably will not
     find what they search. Note that it is possible to create
     zero-length names with `nextname' (should it not?).

`>IN' greater than input buffer:
     The next invocation of a parsing word returns a string with length
     0.

`RECURSE' appears after `DOES>':
     Compiles a recursive call to the defining word, not to the defined
     word.

argument input source different than current input source for `RESTORE-INPUT':
     `-12 THROW'. Note that, once an input file is closed (e.g., because
     the end of the file was reached), its source-id may be reused.
     Therefore, restoring an input source specification referencing a
     closed file may lead to unpredictable results instead of a `-12
     THROW'.

     In the future, Gforth may be able to restore input source
     specifications from other than the current input source.

data space containing definitions gets de-allocated:
     Deallocation with `allot' is not checked. This typically results in
     memory access faults or execution of illegal instructions.

data space read/write with incorrect alignment:
     Processor-dependent. Typically results in a `-23 throw' (Address
     alignment exception). Under Linux-Intel on a 486 or later
     processor with alignment turned on, incorrect alignment results in
     a `-9 throw' (Invalid memory address). There are reportedly some
     processors with alignment restrictions that do not report
     violations.

data space pointer not properly aligned, `,', `C,':
     Like other alignment errors.

less than u+2 stack items (`PICK' and `ROLL'):
     Like other stack underflows.

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.

most recent definition does not have a name (`IMMEDIATE'):
     `abort" last word was headerless"'.

name not defined by `VALUE' used by `TO':
     `-32 throw' (Invalid name argument) (unless name is a local or was
     defined by `CONSTANT'; in the latter case it just changes the
     constant).

name not found (`'', `POSTPONE', `[']', `[COMPILE]'):
     `-13 throw' (Undefined word)

parameters are not of the same type (`DO', `?DO', `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.

`POSTPONE' or `[COMPILE]' applied to `TO':
     Assume `: X POSTPONE TO ; IMMEDIATE'. `X' performs the compilation
     semantics of `TO'.

String longer than a counted string returned by `WORD':
     Not checked. The string will be ok, but the count will, of course,
     contain only the least significant bits of the length.

u greater than or equal to the number of bits in a cell (`LSHIFT', `RSHIFT'):
     Processor-dependent. Typical behaviours are returning 0 and using
     only the low bits of the shift count.

word not defined via `CREATE':
     `>BODY' produces the PFA of the word no matter how it was defined.

     `DOES>' changes the execution semantics of the last defined word no
     matter how it was defined. E.g., `CONSTANT DOES>' is equivalent to
     `CREATE , DOES>'.

words improperly used outside `<#' and `#>':
     Not checked. As usual, you can expect memory faults.


File: gforth.info,  Node: core-other,  Prev: core-ambcond,  Up: The Core Words

Other system documentation
--------------------------

nonstandard words using `PAD':
     None.

operator's terminal facilities available:
     After processing the OS's command line, Gforth goes into
     interactive mode, and you can give commands to Gforth
     interactively. The actual facilities available depend on how you
     invoke Gforth.

program data space available:
     `UNUSED .' gives the remaining dictionary space. The total
     dictionary space can be specified with the `-m' switch (*note
     Invoking Gforth::) when Gforth starts up.

return stack space available:
     You can compute the total return stack space in cells with `s"
     RETURN-STACK-CELLS" environment? drop .'. You can specify it at
     startup time with the `-r' switch (*note Invoking Gforth::).

stack space available:
     You can compute the total data stack space in cells with `s"
     STACK-CELLS" environment? drop .'. You can specify it at startup
     time with the `-d' switch (*note Invoking Gforth::).

system dictionary space required, in address units:
     Type `here forthstart - .' after startup. At the time of this
     writing, this gives 80080 (bytes) on a 32-bit system.


File: gforth.info,  Node: The optional Block word set,  Next: The optional Double Number word set,  Prev: The Core Words,  Up: ANS conformance

The optional Block word set
===========================

* Menu:

* block-idef::                  Implementation Defined Options
* block-ambcond::               Ambiguous Conditions
* block-other::                 Other System Documentation


File: gforth.info,  Node: block-idef,  Next: block-ambcond,  Prev: The optional Block word set,  Up: The optional Block word set

Implementation Defined Options
------------------------------

the format for display by `LIST':
     First the screen number is displayed, then 16 lines of 64
     characters, each line preceded by the line number.

the length of a line affected by `\':
     64 characters.


File: gforth.info,  Node: block-ambcond,  Next: block-other,  Prev: block-idef,  Up: The optional Block word set

Ambiguous conditions
--------------------

correct block read was not possible:
     Typically results in a `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.

I/O exception in block transfer:
     Typically results in a `throw' of some OS-derived value (between
     -512 and -2048).

invalid block number:
     `-35 throw' (Invalid block number)

a program directly alters the contents of `BLK':
     The input stream is switched to that other block, at the same
     position. If the storing to `BLK' happens when interpreting
     non-block input, the system will get quite confused when the block
     ends.

no current block buffer for `UPDATE':
     `UPDATE' has no effect.


File: gforth.info,  Node: block-other,  Prev: block-ambcond,  Up: The optional Block word set

Other system documentation
--------------------------

any restrictions a multiprogramming system places on the use of buffer addresses:
     No restrictions (yet).

the number of blocks available for source and data:
     depends on your disk space.


File: gforth.info,  Node: The optional Double Number word set,  Next: The optional Exception word set,  Prev: The optional Block word set,  Up: ANS conformance

The optional Double Number word set
===================================

* Menu:

* double-ambcond::              Ambiguous Conditions


File: gforth.info,  Node: double-ambcond,  Prev: The optional Double Number word set,  Up: The optional Double Number word set

Ambiguous conditions
--------------------

d outside of range of n in `D>S':
     The least significant cell of d is produced.


File: gforth.info,  Node: The optional Exception word set,  Next: The optional Facility word set,  Prev: The optional Double Number word set,  Up: ANS conformance

The optional Exception word set
===============================

* Menu:

* exception-idef::              Implementation Defined Options


File: gforth.info,  Node: exception-idef,  Prev: The optional Exception word set,  Up: The optional Exception word set

Implementation Defined Options
------------------------------

`THROW'-codes used in the system:
     The codes -256--511 are used for reporting signals. The mapping
     from OS signal numbers to throw codes is -256-signal. The codes
     -512--2047 are used for OS errors (for file and memory allocation
     operations). The mapping from OS error numbers to throw codes is
     -512-`errno'. One side effect of this mapping is that undefined OS
     errors produce a message with a strange number; e.g., `-1000
     THROW' results in `Unknown error 488' on my system.


File: gforth.info,  Node: The optional Facility word set,  Next: The optional File-Access word set,  Prev: The optional Exception word set,  Up: ANS conformance

The optional Facility word set
==============================

* Menu:

* facility-idef::               Implementation Defined Options
* facility-ambcond::            Ambiguous Conditions


File: gforth.info,  Node: facility-idef,  Next: facility-ambcond,  Prev: The optional Facility word set,  Up: The optional Facility word set

Implementation Defined Options
------------------------------

encoding of keyboard events (`EKEY'):
     Keys corresponding to ASCII characters are encoded as ASCII
     characters.  Other keys are encoded with the constants `k-left',
     `k-right', `k-up', `k-down', `k-home', `k-end', `k1', `k2', `k3',
     `k4', `k5', `k6', `k7', `k8', `k9', `k10', `k11', `k12'.

duration of a system clock tick:
     System dependent. With respect to `MS', the time is specified in
     microseconds. How well the OS and the hardware implement this, is
     another question.

repeatability to be expected from the execution of `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.


File: gforth.info,  Node: facility-ambcond,  Prev: facility-idef,  Up: The optional Facility word set

Ambiguous conditions
--------------------

`AT-XY' can't be performed on user output device:
     Largely terminal dependent. No range checks are done on the
     arguments.  No errors are reported. You may see some garbage
     appearing, you may see simply nothing happen.


File: gforth.info,  Node: The optional File-Access word set,  Next: The optional Floating-Point word set,  Prev: The optional Facility word set,  Up: ANS conformance

The optional File-Access word set
=================================

* Menu:

* file-idef::                   Implementation Defined Options
* file-ambcond::                Ambiguous Conditions


File: gforth.info,  Node: file-idef,  Next: file-ambcond,  Prev: The optional File-Access word set,  Up: The optional File-Access word set

Implementation Defined Options
------------------------------

file access methods used:
     `R/O', `R/W' and `BIN' work as you would expect. `W/O' translates
     into the C file opening mode `w' (or `wb'): The file is cleared,
     if it exists, and created, if it does not (with both `open-file'
     and `create-file').  Under Unix `create-file' creates a file with
     666 permissions modified by your umask.

file exceptions:
     The file words do not raise exceptions (except, perhaps, memory
     access faults when you pass illegal addresses or file-ids).

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.

file name format:
     System dependent. Gforth just uses the file name format of your OS.

information returned by `FILE-STATUS':
     `FILE-STATUS' returns the most powerful file access mode allowed
     for the file: Either `R/O', `W/O' or `R/W'. If the file cannot be
     accessed, `R/O BIN' is returned. `BIN' is applicable along with
     the returned mode.

input file state after an exception when including source:
     All files that are left via the exception are closed.

ior values and meaning:
     The iors returned by the file and memory allocation words are
     intended as throw codes. They typically are in the range
     -512--2047 of OS errors.  The mapping from OS error numbers to
     iors is -512-errno.

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.

maximum size of input line:
     `/line'. Currently 255.

methods of mapping block ranges to files:
     By default, blocks are accessed in the file `blocks.fb' in the
     current working directory. The file can be switched with `USE'.

number of string buffers provided by `S"':
     1

size of string buffer used by `S"':
     `/line'. currently 255.


File: gforth.info,  Node: file-ambcond,  Prev: file-idef,  Up: The optional File-Access word set

Ambiguous conditions
--------------------

attempting to position a file outside its boundaries:
     `REPOSITION-FILE' is performed as usual: Afterwards,
     `FILE-POSITION' returns the value given to `REPOSITION-FILE'.

attempting to read from file positions not yet written:
     End-of-file, i.e., zero characters are read and no error is
     reported.

file-id is invalid (`INCLUDE-FILE'):
     An appropriate exception may be thrown, but a memory fault or other
     problem is more probable.

I/O exception reading or closing file-id (`INCLUDE-FILE', `INCLUDED'):
     The ior produced by the operation, that discovered the problem, is
     thrown.

named file cannot be opened (`INCLUDED'):
     The ior produced by `open-file' is thrown.

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.

using `source-id' when `blk' is non-zero:
     `source-id' performs its function. Typically it will give the id of
     the source which loaded the block. (Better ideas?)


File: gforth.info,  Node: The optional Floating-Point word set,  Next: The optional Locals word set,  Prev: The optional File-Access word set,  Up: ANS conformance

The optional Floating-Point word set
====================================

* Menu:

* floating-idef::               Implementation Defined Options
* floating-ambcond::            Ambiguous Conditions


File: gforth.info,  Node: floating-idef,  Next: floating-ambcond,  Prev: The optional Floating-Point word set,  Up: The optional Floating-Point word set

Implementation Defined Options
------------------------------

format and range of floating point numbers:
     System-dependent; the `double' type of C.

results of `REPRESENT' when float is out of range:
     System dependent; `REPRESENT' is implemented using the C library
     function `ecvt()' and inherits its behaviour in this respect.

rounding or truncation of floating-point numbers:
     System dependent; the rounding behaviour is inherited from the
     hosting C compiler. IEEE-FP-based (i.e., most) systems by default
     round to nearest, and break ties by rounding to even (i.e., such
     that the last bit of the mantissa is 0).

size of floating-point stack:
     `s" FLOATING-STACK" environment? drop .' gives the total size of
     the floating-point stack (in floats). You can specify this on
     startup with the command-line option `-f' (*note Invoking
     Gforth::).

width of floating-point stack:
     `1 floats'.


File: gforth.info,  Node: floating-ambcond,  Prev: floating-idef,  Up: The optional Floating-Point word set

Ambiguous conditions
--------------------

`df@' or `df!' used with an address that is not double-float  aligned:
     System-dependent. Typically results in a `-23 THROW' like other
     alignment violations.

`f@' or `f!' used with an address that is not float  aligned:
     System-dependent. Typically results in a `-23 THROW' like other
     alignment violations.

floating-point result out of range:
     System-dependent. Can result in a `-43 throw' (floating point
     overflow), `-54 throw' (floating point underflow), `-41 throw'
     (floating point inexact result), `-55 THROW' (Floating-point
     unidentified fault), or can produce a special value representing,
     e.g., Infinity.

`sf@' or `sf!' used with an address that is not single-float  aligned:
     System-dependent. Typically results in an alignment fault like
     other alignment violations.

`base' is not decimal (`REPRESENT', `F.', `FE.', `FS.'):
     The floating-point number is converted into decimal nonetheless.

Both arguments are equal to zero (`FATAN2'):
     System-dependent. `FATAN2' is implemented using the C library
     function `atan2()'.

Using `FTAN' on an argument r1 where cos(r1) is zero:
     System-dependent. Anyway, typically the cos of r1 will not be zero
     because of small errors and the tan will be a very large (or very
     small) but finite number.

d cannot be presented precisely as a float in `D>F':
     The result is rounded to the nearest float.

dividing by zero:
     Platform-dependent; can produce an Infinity, NaN, `-42 throw'
     (floating point divide by zero) or `-55 throw' (Floating-point
     unidentified fault).

exponent too big for conversion (`DF!', `DF@', `SF!', `SF@'):
     System dependent. On IEEE-FP based systems the number is converted
     into an infinity.

float<1 (`FACOSH'):
     Platform-dependent; on IEEE-FP systems typically produces a NaN.

float=<-1 (`FLNP1'):
     Platform-dependent; on IEEE-FP systems typically produces a NaN
     (or a negative infinity for float=-1).

float=<0 (`FLN', `FLOG'):
     Platform-dependent; on IEEE-FP systems typically produces a NaN
     (or a negative infinity for float=0).

float<0 (`FASINH', `FSQRT'):
     Platform-dependent; for `fsqrt' this typically gives a NaN, for
     `fasinh' some platforms produce a NaN, others a number (bug in the
     C library?).

|float|>1 (`FACOS', `FASIN', `FATANH'):
     Platform-dependent; IEEE-FP systems typically produce a NaN.

integer part of float cannot be represented by d in `F>D':
     Platform-dependent; typically, some double number is produced and
     no error is reported.

string larger than pictured numeric output area (`f.', `fe.', `fs.'):
     `Precision' characters of the numeric output area are used.  If
     `precision' is too high, these words will smash the data or code
     close to `here'.


File: gforth.info,  Node: The optional Locals word set,  Next: The optional Memory-Allocation word set,  Prev: The optional Floating-Point word set,  Up: ANS conformance

The optional Locals word set
============================

* Menu:

* locals-idef::                 Implementation Defined Options
* locals-ambcond::              Ambiguous Conditions


File: gforth.info,  Node: locals-idef,  Next: locals-ambcond,  Prev: The optional Locals word set,  Up: The optional Locals word set

Implementation Defined Options
------------------------------

maximum number of locals in a definition:
     `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.


File: gforth.info,  Node: locals-ambcond,  Prev: locals-idef,  Up: The optional Locals word set

Ambiguous conditions
--------------------

executing a named local in interpretation state:
     Locals have no interpretation semantics. If you try to perform the
     interpretation semantics, you will get a `-14 throw' somewhere
     (Interpreting a compile-only word). If you perform the compilation
     semantics, the locals access will be compiled (irrespective of
     state).

name not defined by `VALUE' or `(LOCAL)' (`TO'):
     `-32 throw' (Invalid name argument)


File: gforth.info,  Node: The optional Memory-Allocation word set,  Next: The optional Programming-Tools word set,  Prev: The optional Locals word set,  Up: ANS conformance

The optional Memory-Allocation word set
=======================================

* Menu:

* memory-idef::                 Implementation Defined Options

