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: Top,  Next: License,  Prev: (dir),  Up: (dir)

   Gforth is a free implementation of ANS Forth available on many
personal machines. This manual corresponds to version 0.5.0.

* Menu:

* License::                     The GPL
* Goals::                       About the Gforth Project
* Gforth Environment::          Starting (and exiting) Gforth
* Tutorial::                    Hands-on Forth Tutorial
* Introduction::                An introduction to ANS Forth
* Words::                       Forth words available in Gforth
* Error messages::              How to interpret them
* Tools::                       Programming tools
* ANS conformance::             Implementation-defined options etc.
* Standard vs Extensions::      Should I use extensions?
* Model::                       The abstract machine of Gforth
* Integrating Gforth::          Forth as scripting language for applications
* Emacs and Gforth::            The Gforth Mode
* Image Files::                 `.fi' files contain compiled code
* Engine::                      The inner interpreter and the primitives
* Binding to System Library::
* Cross Compiler::              The Cross Compiler
* Bugs::                        How to report them
* Origin::                      Authors and ancestors of Gforth
* Forth-related information::   Books and places to look on the WWW
* Word Index::                  An item for each Forth word
* Concept Index::               A menu covering many topics


Gforth Environment

* Invoking Gforth::             Getting in
* Leaving Gforth::              Getting out
* Command-line editing::
* Environment variables::       that affect how Gforth starts up
* Gforth Files::                What gets installed and where
* Startup speed::               When 35ms is not fast enough ...

Forth Tutorial

* Starting Gforth Tutorial::
* Syntax Tutorial::
* Crash Course Tutorial::
* Stack Tutorial::
* Arithmetics Tutorial::
* Stack Manipulation Tutorial::
* Using files for Forth code Tutorial::
* Comments Tutorial::
* Colon Definitions Tutorial::
* Decompilation Tutorial::
* Stack-Effect Comments Tutorial::
* Types Tutorial::
* Factoring Tutorial::
* Designing the stack effect Tutorial::
* Local Variables Tutorial::
* Conditional execution Tutorial::
* Flags and Comparisons Tutorial::
* General Loops Tutorial::
* Counted loops Tutorial::
* Recursion Tutorial::
* Leaving definitions or loops Tutorial::
* Return Stack Tutorial::
* Memory Tutorial::
* Characters and Strings Tutorial::
* Alignment Tutorial::
* Files Tutorial::
* Interpretation and Compilation Semantics and Immediacy Tutorial::
* Execution Tokens Tutorial::
* Exceptions Tutorial::
* Defining Words Tutorial::
* Arrays and Records Tutorial::
* POSTPONE Tutorial::
* Literal Tutorial::
* Advanced macros Tutorial::
* Compilation Tokens Tutorial::
* Wordlists and Search Order Tutorial::

An Introduction to ANS Forth

* Introducing the Text Interpreter::
* Stacks and Postfix notation::
* Your first definition::
* How does that work?::
* Forth is written in Forth::
* Review - elements of a Forth system::
* Where to go next::
* Exercises::

Forth Words

* Notation::
* Case insensitivity::
* Comments::
* Boolean Flags::
* Arithmetic::
* Stack Manipulation::
* Memory::
* Control Structures::
* Defining Words::
* Interpretation and Compilation Semantics::
* Tokens for Words::
* Compiling words::
* The Text Interpreter::
* Word Lists::
* Environmental Queries::
* Files::
* Blocks::
* Other I/O::
* Locals::
* Structures::
* Object-oriented Forth::
* Programming Tools::
* Assembler and Code Words::
* Threading Words::
* Passing Commands to the OS::
* Keeping track of Time::
* Miscellaneous Words::

Arithmetic

* Single precision::
* Double precision::            Double-cell integer arithmetic
* Bitwise operations::
* Numeric comparison::
* Mixed precision::             Operations with single and double-cell integers
* Floating Point::

Stack Manipulation

* Data stack::
* Floating point stack::
* Return stack::
* Locals stack::
* Stack pointer manipulation::

Memory

* Memory model::
* Dictionary allocation::
* Heap Allocation::
* Memory Access::
* Address arithmetic::
* Memory Blocks::

Control Structures

* Selection::                   IF ... ELSE ... ENDIF
* Simple Loops::                BEGIN ...
* Counted Loops::               DO
* Arbitrary control structures::
* Calls and returns::
* Exception Handling::

Defining Words

* CREATE::
* Variables::                   Variables and user variables
* Constants::
* Values::                      Initialised variables
* Colon Definitions::
* Anonymous Definitions::       Definitions without names
* Supplying names::             Passing definition names as strings
* User-defined Defining Words::
* Deferred words::              Allow forward references
* Aliases::

User-defined Defining Words

* CREATE..DOES> applications::
* CREATE..DOES> details::
* Advanced does> usage example::

Interpretation and Compilation Semantics

* Combined words::

Tokens for Words

* Execution token::             represents execution/interpretation semantics
* Compilation token::           represents compilation semantics
* Name token::                  represents named words

Compiling words

* Literals::                    Compiling data values
* Macros::                      Compiling words

The Text Interpreter

* Input Sources::
* Number Conversion::
* Interpret/Compile states::
* Interpreter Directives::

Word Lists

* Vocabularies::
* Why use word lists?::
* Word list example::

Files

* Forth source files::
* General files::
* Search Paths::

Search Paths

* Source Search Paths::
* General Search Paths::

Other I/O

* Simple numeric output::       Predefined formats
* Formatted numeric output::    Formatted (pictured) output
* String Formats::              How Forth stores strings in memory
* Displaying characters and strings::  Other stuff
* Input::                       Input

Locals

* Gforth locals::
* ANS Forth locals::

Gforth locals

* Where are locals visible by name?::
* How long do locals live?::
* Locals programming style::
* Locals implementation::

Structures

* Why explicit structure support?::
* Structure Usage::
* Structure Naming Convention::
* Structure Implementation::
* Structure Glossary::

Object-oriented Forth

* Why object-oriented programming?::
* Object-Oriented Terminology::
* Objects::
* OOF::
* Mini-OOF::
* Comparison with other object models::

The `objects.fs' model

* Properties of the Objects model::
* Basic Objects Usage::
* The Objects base class::
* Creating objects::
* Object-Oriented Programming Style::
* Class Binding::
* Method conveniences::
* Classes and Scoping::
* Dividing classes::
* Object Interfaces::
* Objects Implementation::
* Objects Glossary::

The `oof.fs' model

* Properties of the OOF model::
* Basic OOF Usage::
* The OOF base class::
* Class Declaration::
* Class Implementation::

The `mini-oof.fs' model

* Basic Mini-OOF Usage::
* Mini-OOF Example::
* Mini-OOF Implementation::

Programming Tools

* Examining::
* Forgetting words::
* Debugging::                   Simple and quick.
* Assertions::                  Making your programs self-checking.
* Singlestep Debugger::         Executing your program word by word.

Assembler and Code Words

* Code and ;code::
* Common Assembler::            Assembler Syntax
* Common Disassembler::
* 386 Assembler::               Deviations and special cases
* Alpha Assembler::             Deviations and special cases
* MIPS assembler::              Deviations and special cases
* Other assemblers::            How to write them

Tools

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

ANS conformance

* 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::

The Core Words

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

The optional Block word set

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

The optional Double Number word set

* double-ambcond::              Ambiguous Conditions

The optional Exception word set

* exception-idef::              Implementation Defined Options

The optional Facility word set

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

The optional File-Access word set

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

The optional Floating-Point word set

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

The optional Locals word set

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

The optional Memory-Allocation word set

* memory-idef::                 Implementation Defined Options

The optional Programming-Tools word set

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

The optional Search-Order word set

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

Image Files

* Image Licensing Issues::      Distribution terms for images.
* Image File Background::       Why have image files?
* Non-Relocatable Image Files::  don't always work.
* Data-Relocatable Image Files::  are better.
* Fully Relocatable Image Files::  better yet.
* Stack and Dictionary Sizes::  Setting the default sizes for an image.
* Running Image Files::         `gforth -i file' or file.
* Modifying the Startup Sequence::  and turnkey applications.

Fully Relocatable Image Files

* gforthmi::                    The normal way
* cross.fs::                    The hard way

Engine

* Portability::
* Threading::
* Primitives::
* Performance::

Threading

* Scheduling::
* Direct or Indirect Threaded?::
* DOES>::

Primitives

* Automatic Generation::
* TOS Optimization::
* Produced code::

Cross Compiler

* Using the Cross Compiler::
* How the Cross Compiler Works::


File: gforth.info,  Node: License,  Next: Goals,  Prev: Top,  Up: Top

GNU GENERAL PUBLIC LICENSE
**************************

                         Version 2, June 1991

     Copyright (C) 1989, 1991 Free Software Foundation, Inc.
     59 Temple Place, Suite 330, Boston, MA 02111, USA
     
     Everyone is permitted to copy and distribute verbatim copies
     of this license document, but changing it is not allowed.

Preamble
========

   The licenses for most software are designed to take away your
freedom to share and change it.  By contrast, the GNU General Public
License is intended to guarantee your freedom to share and change free
software--to make sure the software is free for all its users.  This
General Public License applies to most of the Free Software
Foundation's software and to any other program whose authors commit to
using it.  (Some other Free Software Foundation software is covered by
the GNU Library General Public License instead.)  You can apply it to
your programs, too.

   When we speak of free software, we are referring to freedom, not
price.  Our General Public Licenses are designed to make sure that you
have the freedom to distribute copies of free software (and charge for
this service if you wish), that you receive source code or can get it
if you want it, that you can change the software or use pieces of it in
new free programs; and that you know you can do these things.

   To protect your rights, we need to make restrictions that forbid
anyone to deny you these rights or to ask you to surrender the rights.
These restrictions translate to certain responsibilities for you if you
distribute copies of the software, or if you modify it.

   For example, if you distribute copies of such a program, whether
gratis or for a fee, you must give the recipients all the rights that
you have.  You must make sure that they, too, receive or can get the
source code.  And you must show them these terms so they know their
rights.

   We protect your rights with two steps: (1) copyright the software,
and (2) offer you this license which gives you legal permission to copy,
distribute and/or modify the software.

   Also, for each author's protection and ours, we want to make certain
that everyone understands that there is no warranty for this free
software.  If the software is modified by someone else and passed on, we
want its recipients to know that what they have is not the original, so
that any problems introduced by others will not reflect on the original
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   Finally, any free program is threatened constantly by software
patents.  We wish to avoid the danger that redistributors of a free
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program proprietary.  To prevent this, we have made it clear that any
patent must be licensed for everyone's free use or not licensed at all.

   The precise terms and conditions for copying, distribution and
modification follow.

    TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION

  0. This License applies to any program or other work which contains a
     notice placed by the copyright holder saying it may be distributed
     under the terms of this General Public License.  The "Program",
     below, refers to any such program or work, and a "work based on
     the Program" means either the Program or any derivative work under
     copyright law: that is to say, a work containing the Program or a
     portion of it, either verbatim or with modifications and/or
     translated into another language.  (Hereinafter, translation is
     included without limitation in the term "modification".)  Each
     licensee is addressed as "you".

     Activities other than copying, distribution and modification are
     not covered by this License; they are outside its scope.  The act
     of running the Program is not restricted, and the output from the
     Program is covered only if its contents constitute a work based on
     the Program (independent of having been made by running the
     Program).  Whether that is true depends on what the Program does.

  1. You may copy and distribute verbatim copies of the Program's
     source code as you receive it, in any medium, provided that you
     conspicuously and appropriately publish on each copy an appropriate
     copyright notice and disclaimer of warranty; keep intact all the
     notices that refer to this License and to the absence of any
     warranty; and give any other recipients of the Program a copy of
     this License along with the Program.

     You may charge a fee for the physical act of transferring a copy,
     and you may at your option offer warranty protection in exchange
     for a fee.

  2. You may modify your copy or copies of the Program or any portion
     of it, thus forming a work based on the Program, and copy and
     distribute such modifications or work under the terms of Section 1
     above, provided that you also meet all of these conditions:

       a. You must cause the modified files to carry prominent notices
          stating that you changed the files and the date of any change.

       b. You must cause any work that you distribute or publish, that
          in whole or in part contains or is derived from the Program
          or any part thereof, to be licensed as a whole at no charge
          to all third parties under the terms of this License.

       c. If the modified program normally reads commands interactively
          when run, you must cause it, when started running for such
          interactive use in the most ordinary way, to print or display
          an announcement including an appropriate copyright notice and
          a notice that there is no warranty (or else, saying that you
          provide a warranty) and that users may redistribute the
          program under these conditions, and telling the user how to
          view a copy of this License.  (Exception: if the Program
          itself is interactive but does not normally print such an
          announcement, your work based on the Program is not required
          to print an announcement.)

     These requirements apply to the modified work as a whole.  If
     identifiable sections of that work are not derived from the
     Program, and can be reasonably considered independent and separate
     works in themselves, then this License, and its terms, do not
     apply to those sections when you distribute them as separate
     works.  But when you distribute the same sections as part of a
     whole which is a work based on the Program, the distribution of
     the whole must be on the terms of this License, whose permissions
     for other licensees extend to the entire whole, and thus to each
     and every part regardless of who wrote it.

     Thus, it is not the intent of this section to claim rights or
     contest your rights to work written entirely by you; rather, the
     intent is to exercise the right to control the distribution of
     derivative or collective works based on the Program.

     In addition, mere aggregation of another work not based on the
     Program with the Program (or with a work based on the Program) on
     a volume of a storage or distribution medium does not bring the
     other work under the scope of this License.

  3. You may copy and distribute the Program (or a work based on it,
     under Section 2) in object code or executable form under the terms
     of Sections 1 and 2 above provided that you also do one of the
     following:

       a. Accompany it with the complete corresponding machine-readable
          source code, which must be distributed under the terms of
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       b. Accompany it with a written offer, valid for at least three
          years, to give any third party, for a charge no more than your
          cost of physically performing source distribution, a complete
          machine-readable copy of the corresponding source code, to be
          distributed under the terms of Sections 1 and 2 above on a
          medium customarily used for software interchange; or,

       c. Accompany it with the information you received as to the offer
          to distribute corresponding source code.  (This alternative is
          allowed only for noncommercial distribution and only if you
          received the program in object code or executable form with
          such an offer, in accord with Subsection b above.)

     The source code for a work means the preferred form of the work for
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     source code means all the source code for all modules it contains,
     plus any associated interface definition files, plus the scripts
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     source or binary form) with the major components (compiler,
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     runs, unless that component itself accompanies the executable.

     If distribution of executable or object code is made by offering
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     distribution of the source code, even though third parties are not
     compelled to copy the source along with the object code.

  4. You may not copy, modify, sublicense, or distribute the Program
     except as expressly provided under this License.  Any attempt
     otherwise to copy, modify, sublicense or distribute the Program is
     void, and will automatically terminate your rights under this
     License.  However, parties who have received copies, or rights,
     from you under this License will not have their licenses
     terminated so long as such parties remain in full compliance.

  5. You are not required to accept this License, since you have not
     signed it.  However, nothing else grants you permission to modify
     or distribute the Program or its derivative works.  These actions
     are prohibited by law if you do not accept this License.
     Therefore, by modifying or distributing the Program (or any work
     based on the Program), you indicate your acceptance of this
     License to do so, and all its terms and conditions for copying,
     distributing or modifying the Program or works based on it.

  6. Each time you redistribute the Program (or any work based on the
     Program), the recipient automatically receives a license from the
     original licensor to copy, distribute or modify the Program
     subject to these terms and conditions.  You may not impose any
     further restrictions on the recipients' exercise of the rights
     granted herein.  You are not responsible for enforcing compliance
     by third parties to this License.

  7. If, as a consequence of a court judgment or allegation of patent
     infringement or for any other reason (not limited to patent
     issues), conditions are imposed on you (whether by court order,
     agreement or otherwise) that contradict the conditions of this
     License, they do not excuse you from the conditions of this
     License.  If you cannot distribute so as to satisfy simultaneously
     your obligations under this License and any other pertinent
     obligations, then as a consequence you may not distribute the
     Program at all.  For example, if a patent license would not permit
     royalty-free redistribution of the Program by all those who
     receive copies directly or indirectly through you, then the only
     way you could satisfy both it and this License would be to refrain
     entirely from distribution of the Program.

     If any portion of this section is held invalid or unenforceable
     under any particular circumstance, the balance of the section is
     intended to apply and the section as a whole is intended to apply
     in other circumstances.

     It is not the purpose of this section to induce you to infringe any
     patents or other property right claims or to contest validity of
     any such claims; this section has the sole purpose of protecting
     the integrity of the free software distribution system, which is
     implemented by public license practices.  Many people have made
     generous contributions to the wide range of software distributed
     through that system in reliance on consistent application of that
     system; it is up to the author/donor to decide if he or she is
     willing to distribute software through any other system and a
     licensee cannot impose that choice.

     This section is intended to make thoroughly clear what is believed
     to be a consequence of the rest of this License.

  8. If the distribution and/or use of the Program is restricted in
     certain countries either by patents or by copyrighted interfaces,
     the original copyright holder who places the Program under this
     License may add an explicit geographical distribution limitation
     excluding those countries, so that distribution is permitted only
     in or among countries not thus excluded.  In such case, this
     License incorporates the limitation as if written in the body of
     this License.

  9. The Free Software Foundation may publish revised and/or new
     versions of the General Public License from time to time.  Such
     new versions will be similar in spirit to the present version, but
     may differ in detail to address new problems or concerns.

     Each version is given a distinguishing version number.  If the
     Program specifies a version number of this License which applies
     to it and "any later version", you have the option of following
     the terms and conditions either of that version or of any later
     version published by the Free Software Foundation.  If the Program
     does not specify a version number of this License, you may choose
     any version ever published by the Free Software Foundation.

 10. If you wish to incorporate parts of the Program into other free
     programs whose distribution conditions are different, write to the
     author to ask for permission.  For software which is copyrighted
     by the Free Software Foundation, write to the Free Software
     Foundation; we sometimes make exceptions for this.  Our decision
     will be guided by the two goals of preserving the free status of
     all derivatives of our free software and of promoting the sharing
     and reuse of software generally.

                                NO WARRANTY

 11. BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO
     WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE
     LAW.  EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT
     HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT
     WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT
     NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
     FITNESS FOR A PARTICULAR PURPOSE.  THE ENTIRE RISK AS TO THE
     QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU.  SHOULD THE
     PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY
     SERVICING, REPAIR OR CORRECTION.

 12. IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN
     WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY
     MODIFY AND/OR REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE
     LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL,
     INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR
     INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF
     DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU
     OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY
     OTHER PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN
     ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.

                      END OF TERMS AND CONDITIONS

How to Apply These Terms to Your New Programs
=============================================

   If you develop a new program, and you want it to be of the greatest
possible use to the public, the best way to achieve this is to make it
free software which everyone can redistribute and change under these
terms.

   To do so, attach the following notices to the program.  It is safest
to attach them to the start of each source file to most effectively
convey the exclusion of warranty; and each file should have at least
the "copyright" line and a pointer to where the full notice is found.

     ONE LINE TO GIVE THE PROGRAM'S NAME AND A BRIEF IDEA OF WHAT IT DOES.
     Copyright (C) 19YY  NAME OF AUTHOR
     
     This program is free software; you can redistribute it and/or modify
     it under the terms of the GNU General Public License as published by
     the Free Software Foundation; either version 2 of the License, or
     (at your option) any later version.
     
     This program is distributed in the hope that it will be useful,
     but WITHOUT ANY WARRANTY; without even the implied warranty of
     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
     GNU General Public License for more details.
     
     You should have received a copy of the GNU General Public License
     along with this program; if not, write to the Free Software
     Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111, USA.

   Also add information on how to contact you by electronic and paper
mail.

   If the program is interactive, make it output a short notice like
this when it starts in an interactive mode:

     Gnomovision version 69, Copyright (C) 19YY NAME OF AUTHOR
     Gnomovision comes with ABSOLUTELY NO WARRANTY; for details
     type `show w'.
     This is free software, and you are welcome to redistribute it
     under certain conditions; type `show c' for details.

   The hypothetical commands `show w' and `show c' should show the
appropriate parts of the General Public License.  Of course, the
commands you use may be called something other than `show w' and `show
c'; they could even be mouse-clicks or menu items--whatever suits your
program.

   You should also get your employer (if you work as a programmer) or
your school, if any, to sign a "copyright disclaimer" for the program,
if necessary.  Here is a sample; alter the names:

     Yoyodyne, Inc., hereby disclaims all copyright interest in the program
     `Gnomovision' (which makes passes at compilers) written by James Hacker.
     
     SIGNATURE OF TY COON, 1 April 1989
     Ty Coon, President of Vice

   This General Public License does not permit incorporating your
program into proprietary programs.  If your program is a subroutine
library, you may consider it more useful to permit linking proprietary
applications with the library.  If this is what you want to do, use the
GNU Library General Public License instead of this License.


File: gforth.info,  Node: Goals,  Next: Gforth Environment,  Prev: License,  Up: Top

Goals of Gforth
***************

   The goal of the Gforth Project is to develop a standard model for
ANS Forth. This can be split into several subgoals:

   * Gforth should conform to the ANS Forth Standard.

   * It should be a model, i.e. it should define all the
     implementation-dependent things.

   * It should become standard, i.e. widely accepted and used. This goal
     is the most difficult one.

   To achieve these goals Gforth should be
   * Similar to previous models (fig-Forth, F83)

   * Powerful. It should provide for all the things that are considered
     necessary today and even some that are not yet considered
     necessary.

   * Efficient. It should not get the reputation of being exceptionally
     slow.

   * Free.

   * Available on many machines/easy to port.

   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, but it
appears to be quite popular. It has some similarities to and some
differences from previous models. It has some powerful features, but not
yet everything that we envisioned. We certainly have achieved our
execution speed goals (*note Performance::)(1).  It is free and
available on many machines.

   ---------- Footnotes ----------

   (1) However, in 1998 the bar was raised when the major commercial
Forth vendors switched to native code compilers.


File: gforth.info,  Node: Gforth Environment,  Next: Tutorial,  Prev: Goals,  Up: Top

Gforth Environment
******************

   Note: ultimately, the Gforth man page will be auto-generated from the
material in this chapter.

* Menu:

* Invoking Gforth::             Getting in
* Leaving Gforth::              Getting out
* Command-line editing::
* Environment variables::       that affect how Gforth starts up
* Gforth Files::                What gets installed and where
* Startup speed::               When 35ms is not fast enough ...

   For related information about the creation of images see *Note Image
Files::.


File: gforth.info,  Node: Invoking Gforth,  Next: Leaving Gforth,  Prev: Gforth Environment,  Up: Gforth Environment

Invoking Gforth
===============

   Gforth is made up of two parts; an executable "engine" (named
`gforth' or `gforth-fast') and an image file. To start it, you will
usually just say `gforth' - this automatically loads the default image
file `gforth.fi'. In many other cases the default Gforth image will be
invoked like this:
     gforth [file | -e forth-code] ...

This interprets the contents of the files and the Forth code in the
order they are given.

   In addition to the `gforth' engine, there is also an engine called
`gforth-fast', which is faster, but gives less informative error
messages (*note Error messages::).  You should use it for debugged,
performance-critical programs.

   In general, the command line looks like this:

     gforth[-fast] [engine options] [image options]

   The engine options must come before the rest of the command line.
They are:

`--image-file file'
`-i file'
     Loads the Forth image file instead of the default `gforth.fi'
     (*note Image Files::).

`--appl-image file'
     Loads the image file and leaves all further command-line arguments
     to the image (instead of processing them as engine options).  This
     is useful for building executable application images on Unix,
     built with `gforthmi --application ...'.

`--path path'
`-p path'
     Uses path for searching the image file and Forth source code files
     instead of the default in the environment variable `GFORTHPATH' or
     the path specified at installation time (e.g.,
     `/usr/local/share/gforth/0.2.0:.'). A path is given as a list of
     directories, separated by `:' (on Unix) or `;' (on other OSs).

`--dictionary-size size'
`-m size'
     Allocate size space for the Forth dictionary space instead of
     using the default specified in the image (typically 256K). The
     size specification for this and subsequent options consists of an
     integer and a unit (e.g., `4M'). The unit can be one of `b'
     (bytes), `e' (element size, in this case Cells), `k' (kilobytes),
     `M' (Megabytes), `G' (Gigabytes), and `T' (Terabytes). If no unit
     is specified, `e' is used.

`--data-stack-size size'
`-d size'
     Allocate size space for the data stack instead of using the
     default specified in the image (typically 16K).

`--return-stack-size size'
`-r size'
     Allocate size space for the return stack instead of using the
     default specified in the image (typically 15K).

`--fp-stack-size size'
`-f size'
     Allocate size space for the floating point stack instead of using
     the default specified in the image (typically 15.5K). In this case
     the unit specifier `e' refers to floating point numbers.

`--locals-stack-size size'
`-l size'
     Allocate size space for the locals stack instead of using the
     default specified in the image (typically 14.5K).

`--help'
`-h'
     Print a message about the command-line options

`--version'
`-v'
     Print version and exit

`--debug'
     Print some information useful for debugging on startup.

`--offset-image'
     Start the dictionary at a slightly different position than would
     be used otherwise (useful for creating data-relocatable images,
     *note Data-Relocatable Image Files::).

`--no-offset-im'
     Start the dictionary at the normal position.

`--clear-dictionary'
     Initialize all bytes in the dictionary to 0 before loading the
     image (*note Data-Relocatable Image Files::).

`--die-on-signal'
     Normally Gforth handles most signals (e.g., the user interrupt
     SIGINT, or the segmentation violation SIGSEGV) by translating it
     into a Forth `THROW'. With this option, Gforth exits if it
     receives such a signal. This option is useful when the engine
     and/or the image might be severely broken (such that it causes
     another signal before recovering from the first); this option
     avoids endless loops in such cases.

   As explained above, the image-specific command-line arguments for the
default image `gforth.fi' consist of a sequence of filenames and `-e
FORTH-CODE' options that are interpreted in the sequence in which they
are given. The `-e FORTH-CODE' or `--evaluate FORTH-CODE' option
evaluates the Forth code. This option takes only one argument; if you
want to evaluate more Forth words, you have to quote them or use `-e'
several times. To exit after processing the command line (instead of
entering interactive mode) append `-e bye' to the command line.

   If you have several versions of Gforth installed, `gforth' will
invoke the version that was installed last. `gforth-version' invokes a
specific version. If your environment contains the variable
`GFORTHPATH', you may want to override it by using the `--path' option.

   Not yet implemented: On startup the system first executes the system
initialization file (unless the option `--no-init-file' is given; note
that the system resulting from using this option may not be ANS Forth
conformant). Then the user initialization file `.gforth.fs' is
executed, unless the option `--no-rc' is given; this file is searched
for in `.', then in `~', then in the normal path (see above).


File: gforth.info,  Node: Leaving Gforth,  Next: Command-line editing,  Prev: Invoking Gforth,  Up: Gforth Environment

Leaving Gforth
==============

   You can leave Gforth by typing `bye' or `Ctrl-d' (at the start of a
line) or (if you invoked Gforth with the `--die-on-signal' option)
`Ctrl-c'. When you leave Gforth, all of your definitions and data are
discarded.  For ways of saving the state of the system before leaving
Gforth see *Note Image Files::.

`bye'       -         tools-ext       ``bye''
   Return control to the host operating system (if any).


File: gforth.info,  Node: Command-line editing,  Next: Environment variables,  Prev: Leaving Gforth,  Up: Gforth Environment

Command-line editing
====================

   Gforth maintains a history file that records every line that you
type to the text interpreter. This file is preserved between sessions,
and is used to provide a command-line recall facility; if you type
`Ctrl-P' repeatedly you can recall successively older commands from
this (or previous) session(s). The full list of command-line editing
facilities is:

   * `Ctrl-p' ("previous") (or up-arrow) to recall successively older
     commands from the history buffer.

   * `Ctrl-n' ("next") (or down-arrow) to recall successively newer
     commands from the history buffer.

   * `Ctrl-f' (or right-arrow) to move the cursor right,
     non-destructively.

   * `Ctrl-b' (or left-arrow) to move the cursor left,
     non-destructively.

   * `Ctrl-h' (backspace) to delete the character to the left of the
     cursor, closing up the line.

   * `Ctrl-k' to delete ("kill") from the cursor to the end of the line.

   * `Ctrl-a' to move the cursor to the start of the line.

   * `Ctrl-e' to move the cursor to the end of the line.

   * <RET> (`Ctrl-m') or <LFD> (`Ctrl-j') to submit the current line.

   * <TAB> to step through all possible full-word completions of the
     word currently being typed.

   * `Ctrl-d' on an empty line line to terminate Gforth (gracefully,
     using `bye').

   * `Ctrl-x' (or `Ctrl-d' on a non-empty line) to delete the character
     under the cursor.

   When editing, displayable characters are inserted to the left of the
cursor position; the line is always in "insert" (as opposed to
"overstrike") mode.

   On Unix systems, the history file is `~/.gforth-history' by
default(1). You can find out the name and location of your history file
using:

     history-file type \ Unix-class systems
     
     history-file type \ Other systems
     history-dir  type

   If you enter long definitions by hand, you can use a text editor to
paste them out of the history file into a Forth source file for reuse at
a later time.

   Gforth never trims the size of the history file, so you should do
this periodically, if necessary.

   ---------- Footnotes ----------

   (1) i.e. it is stored in the user's home directory.


File: gforth.info,  Node: Environment variables,  Next: Gforth Files,  Prev: Command-line editing,  Up: Gforth Environment

Environment variables
=====================

   Gforth uses these environment variables:

   * `GFORTHHIST' - (Unix systems only) specifies the directory in
     which to open/create the history file, `.gforth-history'. Default:
     `$HOME'.

   * `GFORTHPATH' - specifies the path used when searching for the
     gforth image file and for Forth source-code files.

   * `GFORTH' - used by `gforthmi', *Note gforthmi::.

   * `GFORTHD' - used by `gforthmi', *Note gforthmi::.

   * `TMP', `TEMP' - (non-Unix systems only) used as a potential
     location for the history file.

   All the Gforth environment variables default to sensible values if
they are not set.


File: gforth.info,  Node: Gforth Files,  Next: Startup speed,  Prev: Environment variables,  Up: Gforth Environment

Gforth files
============

   When you install Gforth on a Unix system, it installs files in these
locations by default:

   * `/usr/local/bin/gforth'

   * `/usr/local/bin/gforthmi'

   * `/usr/local/man/man1/gforth.1' - man page.

   * `/usr/local/info' - the Info version of this manual.

   * `/usr/local/lib/gforth/<version>/...' - Gforth `.fi' files.

   * `/usr/local/share/gforth/<version>/TAGS' - Emacs TAGS file.

   * `/usr/local/share/gforth/<version>/...' - Gforth source files.

   * `.../emacs/site-lisp/gforth.el' - Emacs gforth mode.

   You can select different places for installation by using
`configure' options (listed with `configure --help').


File: gforth.info,  Node: Startup speed,  Prev: Gforth Files,  Up: Gforth Environment

Startup speed
=============

   If Gforth is used for CGI scripts or in shell scripts, its startup
speed may become a problem.  On a 300MHz 21064a under Linux-2.2.13 with
glibc-2.0.7, `gforth -e bye' takes about 24.6ms user and 11.3ms system
time.

   If startup speed is a problem, you may consider the following ways to
improve it; or you may consider ways to reduce the number of startups
(for example, by using Fast-CGI).

   The first step to improve startup speed is to statically link
Gforth, by building it with `XLDFLAGS=-static'.  This requires more
memory for the code and will therefore slow down the first invocation,
but subsequent invocations avoid the dynamic linking overhead.  Another
disadvantage is that Gforth won't profit from library upgrades.  As a
result, `gforth-static -e bye' takes about 17.1ms user and 8.2ms system
time.

   The next step to improve startup speed is to use a non-relocatable
image (*note Non-Relocatable Image Files::).  You can create this image
with `gforth -e "savesystem gforthnr.fi bye"' and later use it with
`gforth -i gforthnr.fi ...'.  This avoids the relocation overhead and a
part of the copy-on-write overhead.  The disadvantage is that the
non-relocatable image does not work if the OS gives Gforth a different
address for the dictionary, for whatever reason; so you better provide a
fallback on a relocatable image.  `gforth-static -i gforthnr.fi -e bye'
takes about 15.3ms user and 7.5ms system time.

   The final step is to disable dictionary hashing in Gforth.  Gforth
builds the hash table on startup, which takes much of the startup
overhead. You can do this by commenting out the `include hash.fs' in
`startup.fs' and everything that requires `hash.fs' (at the moment
`table.fs' and `ekey.fs') and then doing `make'.  The disadvantages are
that functionality like `table' and `ekey' is missing and that text
interpretation (e.g., compiling) now takes much longer. So, you should
only use this method if there is no significant text interpretation to
perform (the script should be compiled into the image, amongst other
things).  `gforth-static -i gforthnrnh.fi -e bye' takes about 2.1ms
user and 6.1ms system time.


File: gforth.info,  Node: Tutorial,  Next: Introduction,  Prev: Gforth Environment,  Up: Top

Forth Tutorial
**************

   The difference of this chapter from the Introduction (*note
Introduction::) is that this tutorial is more fast-paced, should be
used while sitting in front of a computer, and covers much more
material, but does not explain how the Forth system works.

   This tutorial can be used with any ANS-compliant Forth; any
Gforth-specific features are marked as such and you can skip them if you
work with another Forth.  This tutorial does not explain all features of
Forth, just enough to get you started and give you some ideas about the
facilities available in Forth.  Read the rest of the manual and the
standard when you are through this.

   The intended way to use this tutorial is that you work through it
while sitting in front of the console, take a look at the examples and
predict what they will do, then try them out; if the outcome is not as
expected, find out why (e.g., by trying out variations of the example),
so you understand what's going on.  There are also some assignments
that you should solve.

   This tutorial assumes that you have programmed before and know what,
e.g., a loop is.

* Menu:

* Starting Gforth Tutorial::
* Syntax Tutorial::
* Crash Course Tutorial::
* Stack Tutorial::
* Arithmetics Tutorial::
* Stack Manipulation Tutorial::
* Using files for Forth code Tutorial::
* Comments Tutorial::
* Colon Definitions Tutorial::
* Decompilation Tutorial::
* Stack-Effect Comments Tutorial::
* Types Tutorial::
* Factoring Tutorial::
* Designing the stack effect Tutorial::
* Local Variables Tutorial::
* Conditional execution Tutorial::
* Flags and Comparisons Tutorial::
* General Loops Tutorial::
* Counted loops Tutorial::
* Recursion Tutorial::
* Leaving definitions or loops Tutorial::
* Return Stack Tutorial::
* Memory Tutorial::
* Characters and Strings Tutorial::
* Alignment Tutorial::
* Files Tutorial::
* Interpretation and Compilation Semantics and Immediacy Tutorial::
* Execution Tokens Tutorial::
* Exceptions Tutorial::
* Defining Words Tutorial::
* Arrays and Records Tutorial::
* POSTPONE Tutorial::
* Literal Tutorial::
* Advanced macros Tutorial::
* Compilation Tokens Tutorial::
* Wordlists and Search Order Tutorial::


File: gforth.info,  Node: Starting Gforth Tutorial,  Next: Syntax Tutorial,  Prev: Tutorial,  Up: Tutorial

Starting Gforth
===============

   You can start Gforth by typing its name:

     gforth

   That puts you into interactive mode; you can leave Gforth by typing
`bye'.  While in Gforth, you can edit the command line and access the
command line history with cursor keys, similar to bash.


File: gforth.info,  Node: Syntax Tutorial,  Next: Crash Course Tutorial,  Prev: Starting Gforth Tutorial,  Up: Tutorial

Syntax
======

   A "word" is a sequence of arbitrary characters (expcept white
space).  Words are separated by white space.  E.g., each of the
following lines contains exactly one word:

     word
     !@#$%^&*()
     1234567890
     5!a

   A frequent beginner's error is to leave away necessary white space,
resulting in an error like `Undefined word'; so if you see such an
error, check if you have put spaces wherever necessary.

     ." hello, world" \ correct
     ."hello, world"  \ gives an "Undefined word" error

   Gforth and most other Forth systems ignore differences in case (they
are case-insensitive), i.e., `word' is the same as `Word'.  If your
system is case-sensitive, you may have to type all the examples given
here in upper case.


File: gforth.info,  Node: Crash Course Tutorial,  Next: Stack Tutorial,  Prev: Syntax Tutorial,  Up: Tutorial

Crash Course
============

   Type

     0 0 !
     here execute
     ' catch >body 20 erase abort
     ' (quit) >body 20 erase

   The last two examples are guaranteed to destroy parts of Gforth (and
most other systems), so you better leave Gforth afterwards (if it has
not finished by itself).  On some systems you may have to kill gforth
from outside (e.g., in Unix with `kill').

   Now that you know how to produce crashes (and that there's not much
to them), let's learn how to produce meaningful programs.


File: gforth.info,  Node: Stack Tutorial,  Next: Arithmetics Tutorial,  Prev: Crash Course Tutorial,  Up: Tutorial

Stack
=====

   The most obvious feature of Forth is the stack.  When you type in a
number, it is pushed on the stack.  You can display the content of the
stack with `.s'.

     1 2 .s
     3 .s

   `.s' displays the top-of-stack to the right, i.e., the numbers
appear in `.s' output as they appeared in the input.

   You can print the top of stack element with `.'.

     1 2 3 . . .

   In general, words consume their stack arguments (`.s' is an
exception).

Assignment:
     What does the stack contain after `5 6 7 .'?


File: gforth.info,  Node: Arithmetics Tutorial,  Next: Stack Manipulation Tutorial,  Prev: Stack Tutorial,  Up: Tutorial

Arithmetics
===========

   The words `+', `-', `*', `/', and `mod' always operate on the top
two stack items:

     2 2 .s
     + .s
     .
     2 1 - .
     7 3 mod .

   The operands of `-', `/', and `mod' are in the same order as in the
corresponding infix expression (this is generally the case in Forth).

   Parentheses are superfluous (and not available), because the order of
the words unambiguously determines the order of evaluation and the
operands:

     3 4 + 5 * .
     3 4 5 * + .

Assignment:
     What are the infix expressions corresponding to the Forth code
     above?  Write `6-7*8+9' in Forth notation(1).

   To change the sign, use `negate':

     2 negate .

Assignment:
     Convert -(-3)*4-5 to Forth.

   `/mod' performs both `/' and `mod'.

     7 3 /mod . .

   Reference: *Note Arithmetic::.

   ---------- Footnotes ----------

   (1) This notation is also known as Postfix or RPN (Reverse Polish
Notation).

