Added ans-report.fs objects.fs: * Tools:: Programming tools 90: * ANS conformance:: Implementation-defined options etc. 91: * Model:: The abstract machine of Gforth 92: * Integrating Gforth:: Forth as scripting language for applications. 93: * Emacs and Gforth:: The Gforth Mode 94: * Internals:: Implementation details 95: * Bugs:: How to report them 96: * Origin:: Authors and ancestors of Gforth 97: * Word Index:: An item for each Forth word 98: * Node Index:: An item for each node 99: @end menu 100: 101: @node License, Goals, Top, Top 102: @unnumbered GNU GENERAL PUBLIC LICENSE 103: @center Version 2, June 1991 104: 105: @display 106: Copyright @copyright{} 1989, 1991 Free Software Foundation, Inc. 107: 675 Mass Ave, Cambridge, MA 02139, USA 108: 109: Everyone is permitted to copy and distribute verbatim copies 110: of this license document, but changing it is not allowed. 111: @end display 112: 113: @unnumberedsec Preamble 114: 115: The licenses for most software are designed to take away your 116: freedom to share and change it. By contrast, the GNU General Public 117: License is intended to guarantee your freedom to share and change free 118: software---to make sure the software is free for all its users. This 119: General Public License applies to most of the Free Software 120: Foundation's software and to any other program whose authors commit to 121: using it. (Some other Free Software Foundation software is covered by 122: the GNU Library General Public License instead.) You can apply it to 123: your programs, too. 124: 125: When we speak of free software, we are referring to freedom, not 126: price. Our General Public Licenses are designed to make sure that you 127: have the freedom to distribute copies of free software (and charge for 128: this service if you wish), that you receive source code or can get it 129: if you want it, that you can change the software or use pieces of it 130: in new free programs; and that you know you can do these things. 131: 132: To protect your rights, we need to make restrictions that forbid 133: anyone to deny you these rights or to ask you to surrender the rights. 134: These restrictions translate to certain responsibilities for you if you 135: distribute copies of the software, or if you modify it. 136: 137: For example, if you distribute copies of such a program, whether 138: gratis or for a fee, you must give the recipients all the rights that 139: you have. You must make sure that they, too, receive or can get the 140: source code. And you must show them these terms so they know their 141: rights. 142: 143: We protect your rights with two steps: (1) copyright the software, and 144: (2) offer you this license which gives you legal permission to copy, 145: distribute and/or modify the software. 146: 147: Also, for each author's protection and ours, we want to make certain 148: that everyone understands that there is no warranty for this free 149: software. If the software is modified by someone else and passed on, we 150: want its recipients to know that what they have is not the original, so 151: that any problems introduced by others will not reflect on the original 152: authors' reputations. 153: 154: Finally, any free program is threatened constantly by software 155: patents. We wish to avoid the danger that redistributors of a free 156: program will individually obtain patent licenses, in effect making the 157: program proprietary. To prevent this, we have made it clear that any 158: patent must be licensed for everyone's free use or not licensed at all. 159: 160: The precise terms and conditions for copying, distribution and 161: modification follow. 162: 163: @iftex 164: @unnumberedsec TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION 165: @end iftex 166: @ifinfo 167: @center TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION 168: @end ifinfo 169: 170: @enumerate 0 171: @item 172: This License applies to any program or other work which contains 173: a notice placed by the copyright holder saying it may be distributed 174: under the terms of this General Public License. The ``Program'', below, 175: refers to any such program or work, and a ``work based on the Program'' 176: means either the Program or any derivative work under copyright law: 177: that is to say, a work containing the Program or a portion of it, 178: either verbatim or with modifications and/or translated into another 179: language. (Hereinafter, translation is included without limitation in 180: the term ``modification''.) Each licensee is addressed as ``you''. 181: 182: Activities other than copying, distribution and modification are not 183: covered by this License; they are outside its scope. The act of 184: running the Program is not restricted, and the output from the Program 185: is covered only if its contents constitute a work based on the 186: Program (independent of having been made by running the Program). 187: Whether that is true depends on what the Program does. 188: 189: @item 190: You may copy and distribute verbatim copies of the Program's 191: source code as you receive it, in any medium, provided that you 192: conspicuously and appropriately publish on each copy an appropriate 193: copyright notice and disclaimer of warranty; keep intact all the 194: notices that refer to this License and to the absence of any warranty; 195: and give any other recipients of the Program a copy of this License 196: along with the Program. 197: 198: You may charge a fee for the physical act of transferring a copy, and 199: you may at your option offer warranty protection in exchange for a fee. 200: 201: @item 202: You may modify your copy or copies of the Program or any portion 203: of it, thus forming a work based on the Program, and copy and 204: distribute such modifications or work under the terms of Section 1 205: above, provided that you also meet all of these conditions: 206: 207: @enumerate a 208: @item 209: You must cause the modified files to carry prominent notices 210: stating that you changed the files and the date of any change. 211: 212: @item 213: You must cause any work that you distribute or publish, that in 214: whole or in part contains or is derived from the Program or any 215: part thereof, to be licensed as a whole at no charge to all third 216: parties under the terms of this License. 217: 218: @item 219: If the modified program normally reads commands interactively 220: when run, you must cause it, when started running for such 221: interactive use in the most ordinary way, to print or display an 222: announcement including an appropriate copyright notice and a 223: notice that there is no warranty (or else, saying that you provide 224: a warranty) and that users may redistribute the program under 225: these conditions, and telling the user how to view a copy of this 226: License. (Exception: if the Program itself is interactive but 227: does not normally print such an announcement, your work based on 228: the Program is not required to print an announcement.) 229: @end enumerate 230: 231: These requirements apply to the modified work as a whole. If 232: identifiable sections of that work are not derived from the Program, 233: and can be reasonably considered independent and separate works in 234: themselves, then this License, and its terms, do not apply to those 235: sections when you distribute them as separate works. But when you 236: distribute the same sections as part of a whole which is a work based 237: on the Program, the distribution of the whole must be on the terms of 238: this License, whose permissions for other licensees extend to the 239: entire whole, and thus to each and every part regardless of who wrote it. 240: 241: Thus, it is not the intent of this section to claim rights or contest 242: your rights to work written entirely by you; rather, the intent is to 243: exercise the right to control the distribution of derivative or 244: collective works based on the Program. 245: 246: In addition, mere aggregation of another work not based on the Program 247: with the Program (or with a work based on the Program) on a volume of 248: a storage or distribution medium does not bring the other work under 249: the scope of this License. 250: 251: @item 252: You may copy and distribute the Program (or a work based on it, 253: under Section 2) in object code or executable form under the terms of 254: Sections 1 and 2 above provided that you also do one of the following: 255: 256: @enumerate a 257: @item 258: Accompany it with the complete corresponding machine-readable 259: source code, which must be distributed under the terms of Sections 260: 1 and 2 above on a medium customarily used for software interchange; or, 261: 262: @item 263: Accompany it with a written offer, valid for at least three 264: years, to give any third party, for a charge no more than your 265: cost of physically performing source distribution, a complete 266: machine-readable copy of the corresponding source code, to be 267: distributed under the terms of Sections 1 and 2 above on a medium 268: customarily used for software interchange; or, 269: 270: @item 271: Accompany it with the information you received as to the offer 272: to distribute corresponding source code. (This alternative is 273: allowed only for noncommercial distribution and only if you 274: received the program in object code or executable form with such 275: an offer, in accord with Subsection b above.) 276: @end enumerate 277: 278: The source code for a work means the preferred form of the work for 279: making modifications to it. For an executable work, complete source 280: code means all the source code for all modules it contains, plus any 281: associated interface definition files, plus the scripts used to 282: control compilation and installation of the executable. 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Any attempt 298: otherwise to copy, modify, sublicense or distribute the Program is 299: void, and will automatically terminate your rights under this License. 300: However, parties who have received copies, or rights, from you under 301: this License will not have their licenses terminated so long as such 302: parties remain in full compliance. 303: 304: @item 305: You are not required to accept this License, since you have not 306: signed it. However, nothing else grants you permission to modify or 307: distribute the Program or its derivative works. These actions are 308: prohibited by law if you do not accept this License. Therefore, by 309: modifying or distributing the Program (or any work based on the 310: Program), you indicate your acceptance of this License to do so, and 311: all its terms and conditions for copying, distributing or modifying 312: the Program or works based on it. 313: 314: @item 315: Each time you redistribute the Program (or any work based on the 316: Program), the recipient automatically receives a license from the 317: original licensor to copy, distribute or modify the Program subject to 318: these terms and conditions. You may not impose any further 319: restrictions on the recipients' exercise of the rights granted herein. 320: You are not responsible for enforcing compliance by third parties to 321: this License. 322: 323: @item 324: If, as a consequence of a court judgment or allegation of patent 325: infringement or for any other reason (not limited to patent issues), 326: conditions are imposed on you (whether by court order, agreement or 327: otherwise) that contradict the conditions of this License, they do not 328: excuse you from the conditions of this License. If you cannot 329: distribute so as to satisfy simultaneously your obligations under this 330: License and any other pertinent obligations, then as a consequence you 331: may not distribute the Program at all. For example, if a patent 332: license would not permit royalty-free redistribution of the Program by 333: all those who receive copies directly or indirectly through you, then 334: the only way you could satisfy both it and this License would be to 335: refrain entirely from distribution of the Program. 336: 337: If any portion of this section is held invalid or unenforceable under 338: any particular circumstance, the balance of the section is intended to 339: apply and the section as a whole is intended to apply in other 340: circumstances. 341: 342: It is not the purpose of this section to induce you to infringe any 343: patents or other property right claims or to contest validity of any 344: such claims; this section has the sole purpose of protecting the 345: integrity of the free software distribution system, which is 346: implemented by public license practices. Many people have made 347: generous contributions to the wide range of software distributed 348: through that system in reliance on consistent application of that 349: system; it is up to the author/donor to decide if he or she is willing 350: to distribute software through any other system and a licensee cannot 351: impose that choice. 352: 353: This section is intended to make thoroughly clear what is believed to 354: be a consequence of the rest of this License. 355: 356: @item 357: If the distribution and/or use of the Program is restricted in 358: certain countries either by patents or by copyrighted interfaces, the 359: original copyright holder who places the Program under this License 360: may add an explicit geographical distribution limitation excluding 361: those countries, so that distribution is permitted only in or among 362: countries not thus excluded. In such case, this License incorporates 363: the limitation as if written in the body of this License. 364: 365: @item 366: The Free Software Foundation may publish revised and/or new versions 367: of the General Public License from time to time. Such new versions will 368: be similar in spirit to the present version, but may differ in detail to 369: address new problems or concerns. 370: 371: Each version is given a distinguishing version number. If the Program 372: specifies a version number of this License which applies to it and ``any 373: later version'', you have the option of following the terms and conditions 374: either of that version or of any later version published by the Free 375: Software Foundation. If the Program does not specify a version number of 376: this License, you may choose any version ever published by the Free Software 377: Foundation. 378: 379: @item 380: If you wish to incorporate parts of the Program into other free 381: programs whose distribution conditions are different, write to the author 382: to ask for permission. For software which is copyrighted by the Free 383: Software Foundation, write to the Free Software Foundation; we sometimes 384: make exceptions for this. Our decision will be guided by the two goals 385: of preserving the free status of all derivatives of our free software and 386: of promoting the sharing and reuse of software generally. 387: 388: @iftex 389: @heading NO WARRANTY 390: @end iftex 391: @ifinfo 392: @center NO WARRANTY 393: @end ifinfo 394: 395: @item 396: BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY 397: FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN 398: OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES 399: PROVIDE THE PROGRAM ``AS IS'' WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED 400: OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF 401: MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS 402: TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE 403: PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, 404: REPAIR OR CORRECTION. 405: 406: @item 407: IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING 408: WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR 409: REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, 410: INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING 411: OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED 412: TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY 413: YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER 414: PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE 415: POSSIBILITY OF SUCH DAMAGES. 416: @end enumerate 417: 418: @iftex 419: @heading END OF TERMS AND CONDITIONS 420: @end iftex 421: @ifinfo 422: @center END OF TERMS AND CONDITIONS 423: @end ifinfo 424: 425: @page 426: @unnumberedsec How to Apply These Terms to Your New Programs 427: 428: If you develop a new program, and you want it to be of the greatest 429: possible use to the public, the best way to achieve this is to make it 430: free software which everyone can redistribute and change under these terms. 431: 432: To do so, attach the following notices to the program. It is safest 433: to attach them to the start of each source file to most effectively 434: convey the exclusion of warranty; and each file should have at least 435: the ``copyright'' line and a pointer to where the full notice is found. 436: 437: @smallexample 438: @var{one line to give the program's name and a brief idea of what it does.} 439: Copyright (C) 19@var{yy} @var{name of author} 440: 441: This program is free software; you can redistribute it and/or modify 442: it under the terms of the GNU General Public License as published by 443: the Free Software Foundation; either version 2 of the License, or 444: (at your option) any later version. 445: 446: This program is distributed in the hope that it will be useful, 447: but WITHOUT ANY WARRANTY; without even the implied warranty of 448: MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 449: GNU General Public License for more details. 450: 451: You should have received a copy of the GNU General Public License 452: along with this program; if not, write to the Free Software 453: Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. 454: @end smallexample 455: 456: Also add information on how to contact you by electronic and paper mail. 457: 458: If the program is interactive, make it output a short notice like this 459: when it starts in an interactive mode: 460: 461: @smallexample 462: Gnomovision version 69, Copyright (C) 19@var{yy} @var{name of author} 463: Gnomovision comes with ABSOLUTELY NO WARRANTY; for details 464: type `show w'. 465: This is free software, and you are welcome to redistribute it 466: under certain conditions; type `show c' for details. 467: @end smallexample 468: 469: The hypothetical commands @samp{show w} and @samp{show c} should show 470: the appropriate parts of the General Public License. Of course, the 471: commands you use may be called something other than @samp{show w} and 472: @samp{show c}; they could even be mouse-clicks or menu items---whatever 473: suits your program. 474: 475: You should also get your employer (if you work as a programmer) or your 476: school, if any, to sign a ``copyright disclaimer'' for the program, if 477: necessary. Here is a sample; alter the names: 478: 479: @smallexample 480: Yoyodyne, Inc., hereby disclaims all copyright interest in the program 481: `Gnomovision' (which makes passes at compilers) written by James Hacker. 482: 483: @var{signature of Ty Coon}, 1 April 1989 484: Ty Coon, President of Vice 485: @end smallexample 486: 487: This General Public License does not permit incorporating your program into 488: proprietary programs. If your program is a subroutine library, you may 489: consider it more useful to permit linking proprietary applications with the 490: library. If this is what you want to do, use the GNU Library General 491: Public License instead of this License. 492: 493: @iftex 494: @node Preface 495: @comment node-name, next, previous, up 496: @unnumbered Preface 497: @cindex Preface 498: This manual documents Gforth. The reader is expected to know 499: Forth. This manual is primarily a reference manual. @xref{Other Books} 500: for introductory material. 501: @end iftex 502: 503: @node Goals, Other Books, License, Top 504: @comment node-name, next, previous, up 505: @chapter Goals of Gforth 506: @cindex Goals 507: The goal of the Gforth Project is to develop a standard model for 508: ANSI Forth. This can be split into several subgoals: 509: 510: @itemize @bullet 511: @item 512: Gforth should conform to the ANSI Forth standard. 513: @item 514: It should be a model, i.e. it should define all the 515: implementation-dependent things. 516: @item 517: It should become standard, i.e. widely accepted and used. This goal 518: is the most difficult one. 519: @end itemize 520: 521: To achieve these goals Gforth should be 522: @itemize @bullet 523: @item 524: Similar to previous models (fig-Forth, F83) 525: @item 526: Powerful. It should provide for all the things that are considered 527: necessary today and even some that are not yet considered necessary. 528: @item 529: Efficient. It should not get the reputation of being exceptionally 530: slow. 531: @item 532: Free. 533: @item 534: Available on many machines/easy to port. 535: @end itemize 536: 537: Have we achieved these goals? Gforth conforms to the ANS Forth 538: standard. It may be considered a model, but we have not yet documented 539: which parts of the model are stable and which parts we are likely to 540: change. It certainly has not yet become a de facto standard. It has some 541: similarities and some differences to previous models. It has some 542: powerful features, but not yet everything that we envisioned. We 543: certainly have achieved our execution speed goals (@pxref{Performance}). 544: It is free and available on many machines. 545: 546: @node Other Books, Invocation, Goals, Top 547: @chapter Other books on ANS Forth 548: 549: As the standard is relatively new, there are not many books out yet. It 550: is not recommended to learn Forth by using Gforth and a book that is 551: not written for ANS Forth, as you will not know your mistakes from the 552: deviations of the book. 553: 554: There is, of course, the standard, the definite reference if you want to 555: write ANS Forth programs. It is available in printed form from the 556: National Standards Institute Sales Department (Tel.: USA (212) 642-4900; 557: Fax.: USA (212) 302-1286) as document @cite{X3.215-1994} for about $200. You 558: can also get it from Global Engineering Documents (Tel.: USA (800) 559: 854-7179; Fax.: (303) 843-9880) for about $300. 560: 561: @cite{dpANS6}, the last draft of the standard, which was then submitted to ANSI 562: for publication is available electronically and for free in some MS Word 563: format, and it has been converted to HTML. Some pointers to these 564: versions can be found through 565: @*@file{}. 566: 567: @cite{Forth: The new model} by Jack Woehr (Prentice-Hall, 1993) is an 568: introductory book based on a draft version of the standard. It does not 569: cover the whole standard. It also contains interesting background 570: information (Jack Woehr was in the ANS Forth Technical Committe). It is 571: not appropriate for complete newbies, but programmers experienced in 572: other languages should find it ok. 573: 574: @node Invocation, Words, Other Books, Top 575: @chapter Invocation 576: 577: You will usually just say @code{gforth}. In many other cases the default 578: Gforth image will be invoked like this: 579: 580: @example 581: gforth [files] [-e forth-code] 582: @end example 583: 584: executing the contents of the files and the Forth code in the order they 585: are given. 586: 587: In general, the command line looks like this: 588: 589: @example 590: gforth [initialization options] [image-specific options] 591: @end example 592: 593: The initialization options must come before the rest of the command 594: line. They are: 595: 596: @table @code 597: @item --image-file @var{file} 598: @item -i @var{file} 599: Loads the Forth image @var{file} instead of the default 600: @file{gforth.fi}. 601: 602: @item --path @var{path} 603: @item -p @var{path} 604: Uses @var{path} for searching the image file and Forth source code files 605: instead of the default in the environment variable @code{GFORTHPATH} or 606: the path specified at installation time (e.g., 607: @file{/usr/local/share/gforth/0.2.0:.}). A path is given as a list of 608: directories, separated by @samp{:} (on Unix) or @samp{;} (on other OSs). 609: 610: @item --dictionary-size @var{size} 611: @item -m @var{size} 612: Allocate @var{size} space for the Forth dictionary space instead of 613: using the default specified in the image (typically 256K). The 614: @var{size} specification consists of an integer and a unit (e.g., 615: @code{4M}). The unit can be one of @code{b} (bytes), @code{e} (element 616: size, in this case Cells), @code{k} (kilobytes), and @code{M} 617: (Megabytes). If no unit is specified, @code{e} is used. 618: 619: @item --data-stack-size @var{size} 620: @item -d @var{size} 621: Allocate @var{size} space for the data stack instead of using the 622: default specified in the image (typically 16K). 623: 624: @item --return-stack-size @var{size} 625: @item -r @var{size} 626: Allocate @var{size} space for the return stack instead of using the 627: default specified in the image (typically 16K). 628: 629: @item --fp-stack-size @var{size} 630: @item -f @var{size} 631: Allocate @var{size} space for the floating point stack instead of 632: using the default specified in the image (typically 16K). In this case 633: the unit specifier @code{e} refers to floating point numbers. 634: 635: @item --locals-stack-size @var{size} 636: @item -l @var{size} 637: Allocate @var{size} space for the locals stack instead of using the 638: default specified in the image (typically 16K). 639: 640: @end table 641: 642: As explained above, the image-specific command-line arguments for the 643: default image @file{gforth.fi} consist of a sequence of filenames and 644: @code{-e @var{forth-code}} options that are interpreted in the seqence 645: in which they are given. The @code{-e @var{forth-code}} or 646: @code{--evaluate @var{forth-code}} option evaluates the forth 647: code. This option takes only one argument; if you want to evaluate more 648: Forth words, you have to quote them or use several @code{-e}s. To exit 649: after processing the command line (instead of entering interactive mode) 650: append @code{-e bye} to the command line. 651: 652: If you have several versions of Gforth installed, @code{gforth} will 653: invoke the version that was installed last. @code{gforth-@var{version}} 654: invokes a specific version. You may want to use the option 655: @code{--path}, if your environment contains the variable 656: @code{GFORTHPATH}. 657: 658: Not yet implemented: 659: On startup the system first executes the system initialization file 660: (unless the option @code{--no-init-file} is given; note that the system 661: resulting from using this option may not be ANS Forth conformant). Then 662: the user initialization file @file{.gforth.fs} is executed, unless the 663: option @code{--no-rc} is given; this file is first searched in @file{.}, 664: then in @file{~}, then in the normal path (see above). 665: 666: @node Words, Tools, Invocation, Top 667: @chapter Forth Words 668: 669: @menu 670: * Notation:: 671: * Arithmetic:: 672: * Stack Manipulation:: 673: * Memory access:: 674: * Control Structures:: 675: * Locals:: 676: * Defining Words:: 677: * Tokens for Words:: 678: * Wordlists:: 679: * Files:: 680: * Blocks:: 681: * Other I/O:: 682: * Programming Tools:: 683: * Assembler and Code words:: 684: * Threading Words:: 685: @end menu 686: 687: @node Notation, Arithmetic, Words, Words 688: @section Notation 689: 690: The Forth words are described in this section in the glossary notation 691: that has become a de-facto standard for Forth texts, i.e. 692: 693: @format 694: @var{word} @var{Stack effect} @var{wordset} @var{pronunciation} 695: @end format 696: @var{Description} 697: 698: @table @var 699: @item word 700: The name of the word. BTW, Gforth is case insensitive, so you can 701: type the words in in lower case (However, @pxref{core-idef}). 702: 703: @item Stack effect 704: The stack effect is written in the notation @code{@var{before} -- 705: @var{after}}, where @var{before} and @var{after} describe the top of 706: stack entries before and after the execution of the word. The rest of 707: the stack is not touched by the word. The top of stack is rightmost, 708: i.e., a stack sequence is written as it is typed in. Note that Gforth 709: uses a separate floating point stack, but a unified stack 710: notation. Also, return stack effects are not shown in @var{stack 711: effect}, but in @var{Description}. The name of a stack item describes 712: the type and/or the function of the item. See below for a discussion of 713: the types. 714: 715: All words have two stack effects: A compile-time stack effect and a 716: run-time stack effect. The compile-time stack-effect of most words is 717: @var{ -- }. If the compile-time stack-effect of a word deviates from 718: this standard behaviour, or the word does other unusual things at 719: compile time, both stack effects are shown; otherwise only the run-time 720: stack effect is shown. 721: 722: @item pronunciation 723: How the word is pronounced 724: 725: @item wordset 726: The ANS Forth standard is divided into several wordsets. A standard 727: system need not support all of them. So, the fewer wordsets your program 728: uses the more portable it will be in theory. However, we suspect that 729: most ANS Forth systems on personal machines will feature all 730: wordsets. Words that are not defined in the ANS standard have 731: @code{gforth} or @code{gforth-internal} as wordset. @code{gforth} 732: describes words that will work in future releases of Gforth; 733: @code{gforth-internal} words are more volatile. Environmental query 734: strings are also displayed like words; you can recognize them by the 735: @code{environment} in the wordset field. 736: 737: @item Description 738: A description of the behaviour of the word. 739: @end table 740: 741: The type of a stack item is specified by the character(s) the name 742: starts with: 743: 744: @table @code 745: @item f 746: Bool, i.e. @code{false} or @code{true}. 747: @item c 748: Char 749: @item w 750: Cell, can contain an integer or an address 751: @item n 752: signed integer 753: @item u 754: unsigned integer 755: @item d 756: double sized signed integer 757: @item ud 758: double sized unsigned integer 759: @item r 760: Float (on the FP stack) 761: @item a_ 762: Cell-aligned address 763: @item c_ 764: Char-aligned address (note that a Char may have two bytes in Windows NT) 765: @item f_ 766: Float-aligned address 767: @item df_ 768: Address aligned for IEEE double precision float 769: @item sf_ 770: Address aligned for IEEE single precision float 771: @item xt 772: Execution token, same size as Cell 773: @item wid 774: Wordlist ID, same size as Cell 775: @item f83name 776: Pointer to a name structure 777: @item " 778: string in the input stream (not the stack). The terminating character is 779: a blank by default. If it is not a blank, it is shown in @code{<>} 780: quotes. 781: 782: @end table 783: 784: @node Arithmetic, Stack Manipulation, Notation, Words 785: @section Arithmetic 786: Forth arithmetic is not checked, i.e., you will not hear about integer 787: overflow on addition or multiplication, you may hear about division by 788: zero if you are lucky. The operator is written after the operands, but 789: the operands are still in the original order. I.e., the infix @code{2-1} 790: corresponds to @code{2 1 -}. Forth offers a variety of division 791: operators. If you perform division with potentially negative operands, 792: you do not want to use @code{/} or @code{/mod} with its undefined 793: behaviour, but rather @code{fm/mod} or @code{sm/mod} (probably the 794: former, @pxref{Mixed precision}). 795: 796: @menu 797: * Single precision:: 798: * Bitwise operations:: 799: * Mixed precision:: operations with single and double-cell integers 800: * Double precision:: Double-cell integer arithmetic 801: * Floating Point:: 802: @end menu 803: 804: @node Single precision, Bitwise operations, Arithmetic, Arithmetic 805: @subsection Single precision 806: doc-+ 807: doc-- 808: doc-* 809: doc-/ 810: doc-mod 811: doc-/mod 812: doc-negate 813: doc-abs 814: doc-min 815: doc-max 816: 817: @node Bitwise operations, Mixed precision, Single precision, Arithmetic 818: @subsection Bitwise operations 819: doc-and 820: doc-or 821: doc-xor 822: doc-invert 823: doc-2* 824: doc-2/ 825: 826: @node Mixed precision, Double precision, Bitwise operations, Arithmetic 827: @subsection Mixed precision 828: doc-m+ 829: doc-*/ 830: doc-*/mod 831: doc-m* 832: doc-um* 833: doc-m*/ 834: doc-um/mod 835: doc-fm/mod 836: doc-sm/rem 837: 838: @node Double precision, Floating Point, Mixed precision, Arithmetic 839: @subsection Double precision 840: 841: The outer (aka text) interpreter converts numbers containing a dot into 842: a double precision number. Note that only numbers with the dot as last 843: character are standard-conforming. 844: 845: doc-d+ 846: doc-d- 847: doc-dnegate 848: doc-dabs 849: doc-dmin 850: doc-dmax 851: 852: @node Floating Point, , Double precision, Arithmetic 853: @subsection Floating Point 854: 855: The format of floating point numbers recognized by the outer (aka text) 856: interpreter is: a signed decimal number, possibly containing a decimal 857: point (@code{.}), followed by @code{E} or @code{e}, optionally followed 858: by a signed integer (the exponent). E.g., @code{1e} ist the same as 859: @code{+1.0e+0}. Note that a number without @code{e} 860: is not interpreted as floating-point number, but as double (if the 861: number contains a @code{.}) or single precision integer. Also, 862: conversions between string and floating point numbers always use base 863: 10, irrespective of the value of @code{BASE}. If @code{BASE} contains a 864: value greater then 14, the @code{E} may be interpreted as digit and the 865: number will be interpreted as integer, unless it has a signed exponent 866: (both @code{+} and @code{-} are allowed as signs). 867: 868: Angles in floating point operations are given in radians (a full circle 869: has 2 pi radians). Note, that Gforth has a separate floating point 870: stack, but we use the unified notation. 871: 872: Floating point numbers have a number of unpleasant surprises for the 873: unwary (e.g., floating point addition is not associative) and even a few 874: for the wary. You should not use them unless you know what you are doing 875: or you don't care that the results you get are totally bogus. If you 876: want to learn about the problems of floating point numbers (and how to 877: avoid them), you might start with @cite{David Goldberg, What Every 878: Computer Scientist Should Know About Floating-Point Arithmetic, ACM 879: Computing Surveys 23(1):5@minus{}48, March 1991}. 880: 881: doc-f+ 882: doc-f- 883: doc-f* 884: doc-f/ 885: doc-fnegate 886: doc-fabs 887: doc-fmax 888: doc-fmin 889: doc-floor 890: doc-fround 891: doc-f** 892: doc-fsqrt 893: doc-fexp 894: doc-fexpm1 895: doc-fln 896: doc-flnp1 897: doc-flog 898: doc-falog 899: doc-fsin 900: doc-fcos 901: doc-fsincos 902: doc-ftan 903: doc-fasin 904: doc-facos 905: doc-fatan 906: doc-fatan2 907: doc-fsinh 908: doc-fcosh 909: doc-ftanh 910: doc-fasinh 911: doc-facosh 912: doc-fatanh 913: 914: @node Stack Manipulation, Memory access, Arithmetic, Words 915: @section Stack Manipulation 916: 917: Gforth has a data stack (aka parameter stack) for characters, cells, 918: addresses, and double cells, a floating point stack for floating point 919: numbers, a return stack for storing the return addresses of colon 920: definitions and other data, and a locals stack for storing local 921: variables. Note that while every sane Forth has a separate floating 922: point stack, this is not strictly required; an ANS Forth system could 923: theoretically keep floating point numbers on the data stack. As an 924: additional difficulty, you don't know how many cells a floating point 925: number takes. It is reportedly possible to write words in a way that 926: they work also for a unified stack model, but we do not recommend trying 927: it. Instead, just say that your program has an environmental dependency 928: on a separate FP stack. 929: 930: Also, a Forth system is allowed to keep the local variables on the 931: return stack. This is reasonable, as local variables usually eliminate 932: the need to use the return stack explicitly. So, if you want to produce 933: a standard complying program and if you are using local variables in a 934: word, forget about return stack manipulations in that word (see the 935: standard document for the exact rules). 936: 937: @menu 938: * Data stack:: 939: * Floating point stack:: 940: * Return stack:: 941: * Locals stack:: 942: * Stack pointer manipulation:: 943: @end menu 944: 945: @node Data stack, Floating point stack, Stack Manipulation, Stack Manipulation 946: @subsection Data stack 947: doc-drop 948: doc-nip 949: doc-dup 950: doc-over 951: doc-tuck 952: doc-swap 953: doc-rot 954: doc--rot 955: doc-?dup 956: doc-pick 957: doc-roll 958: doc-2drop 959: doc-2nip 960: doc-2dup 961: doc-2over 962: doc-2tuck 963: doc-2swap 964: doc-2rot 965: 966: @node Floating point stack, Return stack, Data stack, Stack Manipulation 967: @subsection Floating point stack 968: doc-fdrop 969: doc-fnip 970: doc-fdup 971: doc-fover 972: doc-ftuck 973: doc-fswap 974: doc-frot 975: 976: @node Return stack, Locals stack, Floating point stack, Stack Manipulation 977: @subsection Return stack 978: doc->r 979: doc-r> 980: doc-r@ 981: doc-rdrop 982: doc-2>r 983: doc-2r> 984: doc-2r@ 985: doc-2rdrop 986: 987: @node Locals stack, Stack pointer manipulation, Return stack, Stack Manipulation 988: @subsection Locals stack 989: 990: @node Stack pointer manipulation, , Locals stack, Stack Manipulation 991: @subsection Stack pointer manipulation 992: doc-sp@ 993: doc-sp! 994: doc-fp@ 995: doc-fp! 996: doc-rp@ 997: doc-rp! 998: doc-lp@ 999: doc-lp! 1000: 1001: @node Memory access, Control Structures, Stack Manipulation, Words 1002: @section Memory access 1003: 1004: @menu 1005: * Stack-Memory transfers:: 1006: * Address arithmetic:: 1007: * Memory block access:: 1008: @end menu 1009: 1010: @node Stack-Memory transfers, Address arithmetic, Memory access, Memory access 1011: @subsection Stack-Memory transfers 1012: 1013: doc-@ 1014: doc-! 1015: doc-+! 1016: doc-c@ 1017: doc-c! 1018: doc-2@ 1019: doc-2! 1020: doc-f@ 1021: doc-f! 1022: doc-sf@ 1023: doc-sf! 1024: doc-df@ 1025: doc-df! 1026: 1027: @node Address arithmetic, Memory block access, Stack-Memory transfers, Memory access 1028: @subsection Address arithmetic 1029: 1030: ANS Forth does not specify the sizes of the data types. Instead, it 1031: offers a number of words for computing sizes and doing address 1032: arithmetic. Basically, address arithmetic is performed in terms of 1033: address units (aus); on most systems the address unit is one byte. Note 1034: that a character may have more than one au, so @code{chars} is no noop 1035: (on systems where it is a noop, it compiles to nothing). 1036: 1037: ANS Forth also defines words for aligning addresses for specific 1038: addresses. Many computers require that accesses to specific data types 1039: must only occur at specific addresses; e.g., that cells may only be 1040: accessed at addresses divisible by 4. Even if a machine allows unaligned 1041: accesses, it can usually perform aligned accesses faster. 1042: 1043: For the performance-conscious: alignment operations are usually only 1044: necessary during the definition of a data structure, not during the 1045: (more frequent) accesses to it. 1046: 1047: ANS Forth defines no words for character-aligning addresses. This is not 1048: an oversight, but reflects the fact that addresses that are not 1049: char-aligned have no use in the standard and therefore will not be 1050: created. 1051: 1052: The standard guarantees that addresses returned by @code{CREATE}d words 1053: are cell-aligned; in addition, Gforth guarantees that these addresses 1054: are aligned for all purposes. 1055: 1056: Note that the standard defines a word @code{char}, which has nothing to 1057: do with address arithmetic. 1058: 1059: doc-chars 1060: doc-char+ 1061: doc-cells 1062: doc-cell+ 1063: doc-align 1064: doc-aligned 1065: doc-floats 1066: doc-float+ 1067: doc-falign 1068: doc-faligned 1069: doc-sfloats 1070: doc-sfloat+ 1071: doc-sfalign 1072: doc-sfaligned 1073: doc-dfloats 1074: doc-dfloat+ 1075: doc-dfalign 1076: doc-dfaligned 1077: doc-maxalign 1078: doc-maxaligned 1079: doc-cfalign 1080: doc-cfaligned 1081: doc-address-unit-bits 1082: 1083: @node Memory block access, , Address arithmetic, Memory access 1084: @subsection Memory block access 1085: 1086: doc-move 1087: doc-erase 1088: 1089: While the previous words work on address units, the rest works on 1090: characters. 1091: 1092: doc-cmove 1093: doc-cmove> 1094: doc-fill 1095: doc-blank 1096: 1097: @node Control Structures, Locals, Memory access, Words 1098: @section Control Structures 1099: 1100: Control structures in Forth cannot be used in interpret state, only in 1101: compile state, i.e., in a colon definition. We do not like this 1102: limitation, but have not seen a satisfying way around it yet, although 1103: many schemes have been proposed. 1104: 1105: @menu 1106: * Selection:: 1107: * Simple Loops:: 1108: * Counted Loops:: 1109: * Arbitrary control structures:: 1110: * Calls and returns:: 1111: * Exception Handling:: 1112: @end menu 1113: 1114: @node Selection, Simple Loops, Control Structures, Control Structures 1115: @subsection Selection 1116: 1117: @example 1118: @var{flag} 1119: IF 1120: @var{code} 1121: ENDIF 1122: @end example 1123: or 1124: @example 1125: @var{flag} 1126: IF 1127: @var{code1} 1128: ELSE 1129: @var{code2} 1130: ENDIF 1131: @end example 1132: 1133: You can use @code{THEN} instead of @code{ENDIF}. Indeed, @code{THEN} is 1134: standard, and @code{ENDIF} is not, although it is quite popular. We 1135: recommend using @code{ENDIF}, because it is less confusing for people 1136: who also know other languages (and is not prone to reinforcing negative 1137: prejudices against Forth in these people). Adding @code{ENDIF} to a 1138: system that only supplies @code{THEN} is simple: 1139: @example 1140: : endif POSTPONE then ; immediate 1141: @end example 1142: 1143: [According to @cite{Webster's New Encyclopedic Dictionary}, @dfn{then 1144: (adv.)} has the following meanings: 1145: @quotation 1146: ... 2b: following next after in order ... 3d: as a necessary consequence 1147: (if you were there, then you saw them). 1148: @end quotation 1149: Forth's @code{THEN} has the meaning 2b, whereas @code{THEN} in Pascal 1150: and many other programming languages has the meaning 3d.] 1151: 1152: Gforth also provides the words @code{?dup-if} and @code{?dup-0=-if}, so 1153: you can avoid using @code{?dup}. Using these alternatives is also more 1154: efficient than using @code{?dup}. Definitions in plain standard Forth 1155: for @code{ENDIF}, @code{?DUP-IF} and @code{?DUP-0=-IF} are provided in 1156: @file{compat/control.fs}. 1157: 1158: @example 1159: @var{n} 1160: CASE 1161: @var{n1} OF @var{code1} ENDOF 1162: @var{n2} OF @var{code2} ENDOF 1163: @dots{} 1164: ENDCASE 1165: @end example 1166: 1167: Executes the first @var{codei}, where the @var{ni} is equal to 1168: @var{n}. A default case can be added by simply writing the code after 1169: the last @code{ENDOF}. It may use @var{n}, which is on top of the stack, 1170: but must not consume it. 1171: 1172: @node Simple Loops, Counted Loops, Selection, Control Structures 1173: @subsection Simple Loops 1174: 1175: @example 1176: BEGIN 1177: @var{code1} 1178: @var{flag} 1179: WHILE 1180: @var{code2} 1181: REPEAT 1182: @end example 1183: 1184: @var{code1} is executed and @var{flag} is computed. If it is true, 1185: @var{code2} is executed and the loop is restarted; If @var{flag} is false, execution continues after the @code{REPEAT}. 1186: 1187: @example 1188: BEGIN 1189: @var{code} 1190: @var{flag} 1191: UNTIL 1192: @end example 1193: 1194: @var{code} is executed. The loop is restarted if @code{flag} is false. 1195: 1196: @example 1197: BEGIN 1198: @var{code} 1199: AGAIN 1200: @end example 1201: 1202: This is an endless loop. 1203: 1204: @node Counted Loops, Arbitrary control structures, Simple Loops, Control Structures 1205: @subsection Counted Loops 1206: 1207: The basic counted loop is: 1208: @example 1209: @var{limit} @var{start} 1210: ?DO 1211: @var{body} 1212: LOOP 1213: @end example 1214: 1215: This performs one iteration for every integer, starting from @var{start} 1216: and up to, but excluding @var{limit}. The counter, aka index, can be 1217: accessed with @code{i}. E.g., the loop 1218: @example 1219: 10 0 ?DO 1220: i . 1221: LOOP 1222: @end example 1223: prints 1224: @example 1225: 0 1 2 3 4 5 6 7 8 9 1226: @end example 1227: The index of the innermost loop can be accessed with @code{i}, the index 1228: of the next loop with @code{j}, and the index of the third loop with 1229: @code{k}. 1230: 1231: The loop control data are kept on the return stack, so there are some 1232: restrictions on mixing return stack accesses and counted loop 1233: words. E.g., if you put values on the return stack outside the loop, you 1234: cannot read them inside the loop. If you put values on the return stack 1235: within a loop, you have to remove them before the end of the loop and 1236: before accessing the index of the loop. 1237: 1238: There are several variations on the counted loop: 1239: 1240: @code{LEAVE} leaves the innermost counted loop immediately. 1241: 1242: If @var{start} is greater than @var{limit}, a @code{?DO} loop is entered 1243: (and @code{LOOP} iterates until they become equal by wrap-around 1244: arithmetic). This behaviour is usually not what you want. Therefore, 1245: Gforth offers @code{+DO} and @code{U+DO} (as replacements for 1246: @code{?DO}), which do not enter the loop if @var{start} is greater than 1247: @var{limit}; @code{+DO} is for signed loop parameters, @code{U+DO} for 1248: unsigned loop parameters. 1249: 1250: @code{LOOP} can be replaced with @code{@var{n} +LOOP}; this updates the 1251: index by @var{n} instead of by 1. The loop is terminated when the border 1252: between @var{limit-1} and @var{limit} is crossed. E.g.: 1253: 1254: @code{4 0 +DO i . 2 +LOOP} prints @code{0 2} 1255: 1256: @code{4 1 +DO i . 2 +LOOP} prints @code{1 3} 1257: 1258: The behaviour of @code{@var{n} +LOOP} is peculiar when @var{n} is negative: 1259: 1260: @code{-1 0 ?DO i . -1 +LOOP} prints @code{0 -1} 1261: 1262: @code{ 0 0 ?DO i . -1 +LOOP} prints nothing 1263: 1264: Therefore we recommend avoiding @code{@var{n} +LOOP} with negative 1265: @var{n}. One alternative is @code{@var{u} -LOOP}, which reduces the 1266: index by @var{u} each iteration. The loop is terminated when the border 1267: between @var{limit+1} and @var{limit} is crossed. Gforth also provides 1268: @code{-DO} and @code{U-DO} for down-counting loops. E.g.: 1269: 1270: @code{-2 0 -DO i . 1 -LOOP} prints @code{0 -1} 1271: 1272: @code{-1 0 -DO i . 1 -LOOP} prints @code{0} 1273: 1274: @code{ 0 0 -DO i . 1 -LOOP} prints nothing 1275: 1276: Unfortunately, @code{+DO}, @code{U+DO}, @code{-DO}, @code{U-DO} and 1277: @code{-LOOP} are not in the ANS Forth standard. However, an 1278: implementation for these words that uses only standard words is provided 1279: in @file{compat/loops.fs}. 1280: 1281: @code{?DO} can also be replaced by @code{DO}. @code{DO} always enters 1282: the loop, independent of the loop parameters. Do not use @code{DO}, even 1283: if you know that the loop is entered in any case. Such knowledge tends 1284: to become invalid during maintenance of a program, and then the 1285: @code{DO} will make trouble. 1286: 1287: @code{UNLOOP} is used to prepare for an abnormal loop exit, e.g., via 1288: @code{EXIT}. @code{UNLOOP} removes the loop control parameters from the 1289: return stack so @code{EXIT} can get to its return address. 1290: 1291: Another counted loop is 1292: @example 1293: @var{n} 1294: FOR 1295: @var{body} 1296: NEXT 1297: @end example 1298: This is the preferred loop of native code compiler writers who are too 1299: lazy to optimize @code{?DO} loops properly. In Gforth, this loop 1300: iterates @var{n+1} times; @code{i} produces values starting with @var{n} 1301: and ending with 0. Other Forth systems may behave differently, even if 1302: they support @code{FOR} loops. To avoid problems, don't use @code{FOR} 1303:: 1335: doc-else 1336: doc-while 1337: doc-repeat 1338: 1339: Gforth adds some more control-structure words: 1340: 1341: doc-endif 1342: doc-?dup-if 1343: doc-?dup-0=-if 1344: 1345: Counted loop words constitute a separate group of words: 1346: 1347: doc-?do 1348: doc-+do 1349: doc-u+do 1350: doc--do 1351: doc-u-do 1352: doc-do 1353: doc-for 1354: doc-loop 1355: doc-+loop 1356: doc--loop 1357: doc-next 1358: doc-leave 1359: doc-?leave 1360: doc-unloop 1361: doc-done 1362: 1363: The standard does not allow using @code{cs-pick} and @code{cs-roll} on 1364: @i{do-sys}. Our system allows it, but it's your job to ensure that for 1365: every @code{?DO} etc. there is exactly one @code{UNLOOP} on any path 1366: through the definition (@code{LOOP} etc. compile an @code{UNLOOP} on the 1367: fall-through path). Also, you have to ensure that all @code{LEAVE}s are 1368: resolved (by using one of the loop-ending words or @code{DONE}). 1369: 1370: Another group of control structure words are 1371: 1372: doc-case 1373: doc-endcase 1374: doc-of 1375: doc-endof 1376: 1377: @i{case-sys} and @i{of-sys} cannot be processed using @code{cs-pick} and 1378: @code{cs-roll}. 1379: 1380: @subsubsection Programming Style 1381: 1382: In order to ensure readability we recommend that you do not create 1383: arbitrary control structures directly, but define new control structure 1384: words for the control structure you want and use these words in your 1385: program. 1386: 1387: E.g., instead of writing 1388: 1389: @example 1390: begin 1391: ... 1392: if [ 1 cs-roll ] 1393: ... 1394: again then 1395: @end example 1396: 1397: we recommend defining control structure words, e.g., 1398: 1399: @example 1400: : while ( dest -- orig dest ) 1401: POSTPONE if 1402: 1 cs-roll ; immediate 1403: 1404: : repeat ( orig dest -- ) 1405: POSTPONE again 1406: POSTPONE then ; immediate 1407: @end example 1408: 1409: and then using these to create the control structure: 1410: 1411: @example 1412: begin 1413: ... 1414: while 1415: ... 1416: repeat 1417: @end example 1418: 1419: That's much easier to read, isn't it? Of course, @code{REPEAT} and 1420: @code{WHILE} are predefined, so in this example it would not be 1421: necessary to define them. 1422: 1423: @node Calls and returns, Exception Handling, Arbitrary control structures, Control Structures 1424: @subsection Calls and returns 1425: 1426: A definition can be called simply be writing the name of the 1427: definition. When the end of the definition is reached, it returns. An 1428: earlier return can be forced using 1429: 1430: doc-exit 1431: 1432: Don't forget to clean up the return stack and @code{UNLOOP} any 1433: outstanding @code{?DO}...@code{LOOP}s before @code{EXIT}ing. The 1434: primitive compiled by @code{EXIT} is 1435: 1436: doc-;s 1437: 1438: @node Exception Handling, , Calls and returns, Control Structures 1439: @subsection Exception Handling 1440: 1441: doc-catch 1442: doc-throw 1443: 1444: @node Locals, Defining Words, Control Structures, Words 1445: @section Locals 1446: 1447: Local variables can make Forth programming more enjoyable and Forth 1448: programs easier to read. Unfortunately, the locals of ANS Forth are 1449: laden with restrictions. Therefore, we provide not only the ANS Forth 1450: locals wordset, but also our own, more powerful locals wordset (we 1451: implemented the ANS Forth locals wordset through our locals wordset). 1452: 1453: The ideas in this section have also been published in the paper 1454: @cite{Automatic Scoping of Local Variables} by M. Anton Ertl, presented 1455: at EuroForth '94; it is available at 1456: @*@file{}. 1457: 1458: @menu 1459: * Gforth locals:: 1460: * ANS Forth locals:: 1461: @end menu 1462: 1463: @node Gforth locals, ANS Forth locals, Locals, Locals 1464: @subsection Gforth locals 1465: 1466: Locals can be defined with 1467: 1468: @example 1469: @{ local1 local2 ... -- comment @} 1470: @end example 1471: or 1472: @example 1473: @{ local1 local2 ... @} 1474: @end example 1475: 1476: E.g., 1477: @example 1478: : max @{ n1 n2 -- n3 @} 1479: n1 n2 > if 1480: n1 1481: else 1482: n2 1483: endif ; 1484: @end example 1485: 1486: The similarity of locals definitions with stack comments is intended. A 1487: locals definition often replaces the stack comment of a word. The order 1488: of the locals corresponds to the order in a stack comment and everything 1489: after the @code{--} is really a comment. 1490: 1491: This similarity has one disadvantage: It is too easy to confuse locals 1492: declarations with stack comments, causing bugs and making them hard to 1493: find. However, this problem can be avoided by appropriate coding 1494: conventions: Do not use both notations in the same program. If you do, 1495: they should be distinguished using additional means, e.g. by position. 1496: 1497: The name of the local may be preceded by a type specifier, e.g., 1498: @code{F:} for a floating point value: 1499: 1500: @example 1501: : CX* @{ F: Ar F: Ai F: Br F: Bi -- Cr Ci @} 1502: \ complex multiplication 1503: Ar Br f* Ai Bi f* f- 1504: Ar Bi f* Ai Br f* f+ ; 1505: @end example 1506: 1507: Gforth currently supports cells (@code{W:}, @code{W^}), doubles 1508: (@code{D:}, @code{D^}), floats (@code{F:}, @code{F^}) and characters 1509: (@code{C:}, @code{C^}) in two flavours: a value-flavoured local (defined 1510: with @code{W:}, @code{D:} etc.) produces its value and can be changed 1511: with @code{TO}. A variable-flavoured local (defined with @code{W^} etc.) 1512: produces its address (which becomes invalid when the variable's scope is 1513: left). E.g., the standard word @code{emit} can be defined in therms of 1514: @code{type} like this: 1515: 1516: @example 1517: : emit @{ C^ char* -- @} 1518: char* 1 type ; 1519: @end example 1520: 1521: A local without type specifier is a @code{W:} local. Both flavours of 1522: locals are initialized with values from the data or FP stack. 1523: 1524: Currently there is no way to define locals with user-defined data 1525: structures, but we are working on it. 1526: 1527: Gforth allows defining locals everywhere in a colon definition. This 1528: poses the following questions: 1529: 1530: @menu 1531: * Where are locals visible by name?:: 1532: * How long do locals live?:: 1533: * Programming Style:: 1534: * Implementation:: 1535: @end menu 1536: 1537: @node Where are locals visible by name?, How long do locals live?, Gforth locals, Gforth locals 1538: @subsubsection Where are locals visible by name? 1539: 1540: Basically, the answer is that locals are visible where you would expect 1541: it in block-structured languages, and sometimes a little longer. If you 1542: want to restrict the scope of a local, enclose its definition in 1543: @code{SCOPE}...@code{ENDSCOPE}. 1544: 1545: doc-scope 1546: doc-endscope 1547: 1548: These words behave like control structure words, so you can use them 1549: with @code{CS-PICK} and @code{CS-ROLL} to restrict the scope in 1550: arbitrary ways. 1551: 1552: If you want a more exact answer to the visibility question, here's the 1553: basic principle: A local is visible in all places that can only be 1554: reached through the definition of the local@footnote{In compiler 1555: construction terminology, all places dominated by the definition of the 1556: local.}. In other words, it is not visible in places that can be reached 1557: without going through the definition of the local. E.g., locals defined 1558: in @code{IF}...@code{ENDIF} are visible until the @code{ENDIF}, locals 1559: defined in @code{BEGIN}...@code{UNTIL} are visible after the 1560: @code{UNTIL} (until, e.g., a subsequent @code{ENDSCOPE}). 1561: 1562: The reasoning behind this solution is: We want to have the locals 1563: visible as long as it is meaningful. The user can always make the 1564: visibility shorter by using explicit scoping. In a place that can 1565: only be reached through the definition of a local, the meaning of a 1566: local name is clear. In other places it is not: How is the local 1567: initialized at the control flow path that does not contain the 1568: definition? Which local is meant, if the same name is defined twice in 1569: two independent control flow paths? 1570: 1571: This should be enough detail for nearly all users, so you can skip the 1572: rest of this section. If you relly must know all the gory details and 1573: options, read on. 1574: 1575: In order to implement this rule, the compiler has to know which places 1576: are unreachable. It knows this automatically after @code{AHEAD}, 1577: @code{AGAIN}, @code{EXIT} and @code{LEAVE}; in other cases (e.g., after 1578: most @code{THROW}s), you can use the word @code{UNREACHABLE} to tell the 1579: compiler that the control flow never reaches that place. If 1580: @code{UNREACHABLE} is not used where it could, the only consequence is 1581: that the visibility of some locals is more limited than the rule above 1582: says. If @code{UNREACHABLE} is used where it should not (i.e., if you 1583: lie to the compiler), buggy code will be produced. 1584: 1585: Another problem with this rule is that at @code{BEGIN}, the compiler 1586: does not know which locals will be visible on the incoming 1587: back-edge. All problems discussed in the following are due to this 1588: ignorance of the compiler (we discuss the problems using @code{BEGIN} 1589: loops as examples; the discussion also applies to @code{?DO} and other 1590: loops). Perhaps the most insidious example is: 1591: @example 1592: AHEAD 1593: BEGIN 1594: x 1595: [ 1 CS-ROLL ] THEN 1596: @{ x @} 1597: ... 1598: UNTIL 1599: @end example 1600: 1601: This should be legal according to the visibility rule. The use of 1602: @code{x} can only be reached through the definition; but that appears 1603: textually below the use. 1604: 1605: From this example it is clear that the visibility rules cannot be fully 1606: implemented without major headaches. Our implementation treats common 1607: cases as advertised and the exceptions are treated in a safe way: The 1608: compiler makes a reasonable guess about the locals visible after a 1609: @code{BEGIN}; if it is too pessimistic, the 1610: user will get a spurious error about the local not being defined; if the 1611: compiler is too optimistic, it will notice this later and issue a 1612: warning. In the case above the compiler would complain about @code{x} 1613: being undefined at its use. You can see from the obscure examples in 1614: this section that it takes quite unusual control structures to get the 1615: compiler into trouble, and even then it will often do fine. 1616: 1617: If the @code{BEGIN} is reachable from above, the most optimistic guess 1618: is that all locals visible before the @code{BEGIN} will also be 1619: visible after the @code{BEGIN}. This guess is valid for all loops that 1620: are entered only through the @code{BEGIN}, in particular, for normal 1621: @code{BEGIN}...@code{WHILE}...@code{REPEAT} and 1622: @code{BEGIN}...@code{UNTIL} loops and it is implemented in our 1623: compiler. When the branch to the @code{BEGIN} is finally generated by 1624: @code{AGAIN} or @code{UNTIL}, the compiler checks the guess and 1625: warns the user if it was too optimisitic: 1626: @example 1627: IF 1628: @{ x @} 1629: BEGIN 1630: \ x ? 1631: [ 1 cs-roll ] THEN 1632: ... 1633: UNTIL 1634: @end example 1635: 1636: Here, @code{x} lives only until the @code{BEGIN}, but the compiler 1637: optimistically assumes that it lives until the @code{THEN}. It notices 1638: this difference when it compiles the @code{UNTIL} and issues a 1639: warning. The user can avoid the warning, and make sure that @code{x} 1640: is not used in the wrong area by using explicit scoping: 1641: @example 1642: IF 1643: SCOPE 1644: @{ x @} 1645: ENDSCOPE 1646: BEGIN 1647: [ 1 cs-roll ] THEN 1648: ... 1649: UNTIL 1650: @end example 1651: 1652: Since the guess is optimistic, there will be no spurious error messages 1653: about undefined locals. 1654: 1655: If the @code{BEGIN} is not reachable from above (e.g., after 1656: @code{AHEAD} or @code{EXIT}), the compiler cannot even make an 1657: optimistic guess, as the locals visible after the @code{BEGIN} may be 1658: defined later. Therefore, the compiler assumes that no locals are 1659: visible after the @code{BEGIN}. However, the user can use 1660: @code{ASSUME-LIVE} to make the compiler assume that the same locals are 1661: visible at the BEGIN as at the point where the top control-flow stack 1662: item was created. 1663: 1664: doc-assume-live 1665: 1666: E.g., 1667: @example 1668: @{ x @} 1669: AHEAD 1670: ASSUME-LIVE 1671: BEGIN 1672: x 1673: [ 1 CS-ROLL ] THEN 1674: ... 1675: UNTIL 1676: @end example 1677: 1678: Other cases where the locals are defined before the @code{BEGIN} can be 1679: handled by inserting an appropriate @code{CS-ROLL} before the 1680: @code{ASSUME-LIVE} (and changing the control-flow stack manipulation 1681: behind the @code{ASSUME-LIVE}). 1682: 1683: Cases where locals are defined after the @code{BEGIN} (but should be 1684: visible immediately after the @code{BEGIN}) can only be handled by 1685: rearranging the loop. E.g., the ``most insidious'' example above can be 1686: arranged into: 1687: @example 1688: BEGIN 1689: @{ x @} 1690: ... 0= 1691: WHILE 1692: x 1693: REPEAT 1694: @end example 1695: 1696: @node How long do locals live?, Programming Style, Where are locals visible by name?, Gforth locals 1697: @subsubsection How long do locals live? 1698: 1699: The right answer for the lifetime question would be: A local lives at 1700: least as long as it can be accessed. For a value-flavoured local this 1701: means: until the end of its visibility. However, a variable-flavoured 1702: local could be accessed through its address far beyond its visibility 1703: scope. Ultimately, this would mean that such locals would have to be 1704: garbage collected. Since this entails un-Forth-like implementation 1705: complexities, I adopted the same cowardly solution as some other 1706: languages (e.g., C): The local lives only as long as it is visible; 1707: afterwards its address is invalid (and programs that access it 1708: afterwards are erroneous). 1709: 1710: @node Programming Style, Implementation, How long do locals live?, Gforth locals 1711: @subsubsection Programming Style 1712: 1713: The freedom to define locals anywhere has the potential to change 1714: programming styles dramatically. In particular, the need to use the 1715: return stack for intermediate storage vanishes. Moreover, all stack 1716: manipulations (except @code{PICK}s and @code{ROLL}s with run-time 1717: determined arguments) can be eliminated: If the stack items are in the 1718: wrong order, just write a locals definition for all of them; then 1719: write the items in the order you want. 1720: 1721: This seems a little far-fetched and eliminating stack manipulations is 1722: unlikely to become a conscious programming objective. Still, the number 1723: of stack manipulations will be reduced dramatically if local variables 1724: are used liberally (e.g., compare @code{max} in @ref{Gforth locals} with 1725: a traditional implementation of @code{max}). 1726: 1727: This shows one potential benefit of locals: making Forth programs more 1728: readable. Of course, this benefit will only be realized if the 1729: programmers continue to honour the principle of factoring instead of 1730: using the added latitude to make the words longer. 1731: 1732: Using @code{TO} can and should be avoided. Without @code{TO}, 1733: every value-flavoured local has only a single assignment and many 1734: advantages of functional languages apply to Forth. I.e., programs are 1735: easier to analyse, to optimize and to read: It is clear from the 1736: definition what the local stands for, it does not turn into something 1737: different later. 1738: 1739: E.g., a definition using @code{TO} might look like this: 1740: @example 1741: : strcmp @{ addr1 u1 addr2 u2 -- n @} 1742: u1 u2 min 0 1743: ?do 1744: addr1 c@@ addr2 c@@ - 1745: ?dup-if 1746: unloop exit 1747: then 1748: addr1 char+ TO addr1 1749: addr2 char+ TO addr2 1750: loop 1751: u1 u2 - ; 1752: @end example 1753: Here, @code{TO} is used to update @code{addr1} and @code{addr2} at 1754: every loop iteration. @code{strcmp} is a typical example of the 1755: readability problems of using @code{TO}. When you start reading 1756: @code{strcmp}, you think that @code{addr1} refers to the start of the 1757: string. Only near the end of the loop you realize that it is something 1758: else. 1759: 1760: This can be avoided by defining two locals at the start of the loop that 1761: are initialized with the right value for the current iteration. 1762: @example 1763: : strcmp @{ addr1 u1 addr2 u2 -- n @} 1764: addr1 addr2 1765: u1 u2 min 0 1766: ?do @{ s1 s2 @} 1767: s1 c@@ s2 c@@ - 1768: ?dup-if 1769: unloop exit 1770: then 1771: s1 char+ s2 char+ 1772: loop 1773: 2drop 1774: u1 u2 - ; 1775: @end example 1776: Here it is clear from the start that @code{s1} has a different value 1777: in every loop iteration. 1778: 1779: @node Implementation, , Programming Style, Gforth locals 1780: @subsubsection Implementation 1781: 1782: Gforth uses an extra locals stack. The most compelling reason for 1783: this is that the return stack is not float-aligned; using an extra stack 1784: also eliminates the problems and restrictions of using the return stack 1785: as locals stack. Like the other stacks, the locals stack grows toward 1786: lower addresses. A few primitives allow an efficient implementation: 1787: 1788: doc-@local# 1789: doc-f@local# 1790: doc-laddr# 1791: doc-lp+!# 1792: doc-lp! 1793: doc->l 1794: doc-f>l 1795: 1796: In addition to these primitives, some specializations of these 1797: primitives for commonly occurring inline arguments are provided for 1798: efficiency reasons, e.g., @code{@@local0} as specialization of 1799: @code{@@local#} for the inline argument 0. The following compiling words 1800: compile the right specialized version, or the general version, as 1801: appropriate: 1802: 1803: doc-compile-@local 1804: doc-compile-f@local 1805: doc-compile-lp+! 1806: 1807: Combinations of conditional branches and @code{lp+!#} like 1808: @code{?branch-lp+!#} (the locals pointer is only changed if the branch 1809: is taken) are provided for efficiency and correctness in loops. 1810: 1811: A special area in the dictionary space is reserved for keeping the 1812: local variable names. @code{@{} switches the dictionary pointer to this 1813: area and @code{@}} switches it back and generates the locals 1814: initializing code. @code{W:} etc.@ are normal defining words. This 1815: special area is cleared at the start of every colon definition. 1816: 1817: A special feature of Gforth's dictionary is used to implement the 1818: definition of locals without type specifiers: every wordlist (aka 1819: vocabulary) has its own methods for searching 1820: etc. (@pxref{Wordlists}). For the present purpose we defined a wordlist 1821: with a special search method: When it is searched for a word, it 1822: actually creates that word using @code{W:}. @code{@{} changes the search 1823: order to first search the wordlist containing @code{@}}, @code{W:} etc., 1824: and then the wordlist for defining locals without type specifiers. 1825: 1826: The lifetime rules support a stack discipline within a colon 1827: definition: The lifetime of a local is either nested with other locals 1828: lifetimes or it does not overlap them. 1829: 1830: At @code{BEGIN}, @code{IF}, and @code{AHEAD} no code for locals stack 1831: pointer manipulation is generated. Between control structure words 1832: locals definitions can push locals onto the locals stack. @code{AGAIN} 1833: is the simplest of the other three control flow words. It has to 1834: restore the locals stack depth of the corresponding @code{BEGIN} 1835: before branching. The code looks like this: 1836: @format 1837: @code{lp+!#} current-locals-size @minus{} dest-locals-size 1838: @code{branch} <begin> 1839: @end format 1840: 1841: @code{UNTIL} is a little more complicated: If it branches back, it 1842: must adjust the stack just like @code{AGAIN}. But if it falls through, 1843: the locals stack must not be changed. The compiler generates the 1844: following code: 1845: @format 1846: @code{?branch-lp+!#} <begin> current-locals-size @minus{} dest-locals-size 1847: @end format 1848: The locals stack pointer is only adjusted if the branch is taken. 1849: 1850: @code{THEN} can produce somewhat inefficient code: 1851: @format 1852: @code{lp+!#} current-locals-size @minus{} orig-locals-size 1853: <orig target>: 1854: @code{lp+!#} orig-locals-size @minus{} new-locals-size 1855: @end format 1856: The second @code{lp+!#} adjusts the locals stack pointer from the 1857: level at the @var{orig} point to the level after the @code{THEN}. The 1858: first @code{lp+!#} adjusts the locals stack pointer from the current 1859: level to the level at the orig point, so the complete effect is an 1860: adjustment from the current level to the right level after the 1861: @code{THEN}. 1862: 1863: In a conventional Forth implementation a dest control-flow stack entry 1864: is just the target address and an orig entry is just the address to be 1865: patched. Our locals implementation adds a wordlist to every orig or dest 1866: item. It is the list of locals visible (or assumed visible) at the point 1867: described by the entry. Our implementation also adds a tag to identify 1868: the kind of entry, in particular to differentiate between live and dead 1869: (reachable and unreachable) orig entries. 1870: 1871: A few unusual operations have to be performed on locals wordlists: 1872: 1873: doc-common-list 1874: doc-sub-list? 1875: doc-list-size 1876: 1877: Several features of our locals wordlist implementation make these 1878: operations easy to implement: The locals wordlists are organised as 1879: linked lists; the tails of these lists are shared, if the lists 1880: contain some of the same locals; and the address of a name is greater 1881: than the address of the names behind it in the list. 1882: 1883: Another important implementation detail is the variable 1884: @code{dead-code}. It is used by @code{BEGIN} and @code{THEN} to 1885: determine if they can be reached directly or only through the branch 1886: that they resolve. @code{dead-code} is set by @code{UNREACHABLE}, 1887: @code{AHEAD}, @code{EXIT} etc., and cleared at the start of a colon 1888: definition, by @code{BEGIN} and usually by @code{THEN}. 1889: 1890: Counted loops are similar to other loops in most respects, but 1891: @code{LEAVE} requires special attention: It performs basically the same 1892: service as @code{AHEAD}, but it does not create a control-flow stack 1893: entry. Therefore the information has to be stored elsewhere; 1894: traditionally, the information was stored in the target fields of the 1895: branches created by the @code{LEAVE}s, by organizing these fields into a 1896: linked list. Unfortunately, this clever trick does not provide enough 1897: space for storing our extended control flow information. Therefore, we 1898: introduce another stack, the leave stack. It contains the control-flow 1899: stack entries for all unresolved @code{LEAVE}s. 1900: 1901: Local names are kept until the end of the colon definition, even if 1902: they are no longer visible in any control-flow path. In a few cases 1903: this may lead to increased space needs for the locals name area, but 1904: usually less than reclaiming this space would cost in code size. 1905: 1906: 1907: @node ANS Forth locals, , Gforth locals, Locals 1908: @subsection ANS Forth locals 1909: 1910: The ANS Forth locals wordset does not define a syntax for locals, but 1911: words that make it possible to define various syntaxes. One of the 1912: possible syntaxes is a subset of the syntax we used in the Gforth locals 1913: wordset, i.e.: 1914: 1915: @example 1916: @{ local1 local2 ... -- comment @} 1917: @end example 1918: or 1919: @example 1920: @{ local1 local2 ... @} 1921: @end example 1922: 1923: The order of the locals corresponds to the order in a stack comment. The 1924: restrictions are: 1925: 1926: @itemize @bullet 1927: @item 1928: Locals can only be cell-sized values (no type specifiers are allowed). 1929: @item 1930: Locals can be defined only outside control structures. 1931: @item 1932: Locals can interfere with explicit usage of the return stack. For the 1933: exact (and long) rules, see the standard. If you don't use return stack 1934: accessing words in a definition using locals, you will be all right. The 1935: purpose of this rule is to make locals implementation on the return 1936: stack easier. 1937: @item 1938: The whole definition must be in one line. 1939: @end itemize 1940: 1941: Locals defined in this way behave like @code{VALUE}s (@xref{Simple 1942: Defining Words}). I.e., they are initialized from the stack. Using their 1943: name produces their value. Their value can be changed using @code{TO}. 1944: 1945: Since this syntax is supported by Gforth directly, you need not do 1946: anything to use it. If you want to port a program using this syntax to 1947: another ANS Forth system, use @file{compat/anslocal.fs} to implement the 1948: syntax on the other system. 1949: 1950: Note that a syntax shown in the standard, section A.13 looks 1951: similar, but is quite different in having the order of locals 1952: reversed. Beware! 1953: 1954: The ANS Forth locals wordset itself consists of the following word 1955: 1956: doc-(local) 1957: 1958: The ANS Forth locals extension wordset defines a syntax, but it is so 1959: awful that we strongly recommend not to use it. We have implemented this 1960: syntax to make porting to Gforth easy, but do not document it here. The 1961: problem with this syntax is that the locals are defined in an order 1962: reversed with respect to the standard stack comment notation, making 1963: programs harder to read, and easier to misread and miswrite. The only 1964: merit of this syntax is that it is easy to implement using the ANS Forth 1965: locals wordset. 1966: 1967: @node Defining Words, Tokens for Words, Locals, Words 1968: @section Defining Words 1969: 1970: @menu 1971: * Simple Defining Words:: 1972: * Colon Definitions:: 1973: * User-defined Defining Words:: 1974: * Supplying names:: 1975: * Interpretation and Compilation Semantics:: 1976: @end menu 1977: 1978: @node Simple Defining Words, Colon Definitions, Defining Words, Defining Words 1979: @subsection Simple Defining Words 1980: 1981: doc-constant 1982: doc-2constant 1983: doc-fconstant 1984: doc-variable 1985: doc-2variable 1986: doc-fvariable 1987: doc-create 1988: doc-user 1989: doc-value 1990: doc-to 1991: doc-defer 1992: doc-is 1993: 1994: @node Colon Definitions, User-defined Defining Words, Simple Defining Words, Defining Words 1995: @subsection Colon Definitions 1996: 1997: @example 1998: : name ( ... -- ... ) 1999: word1 word2 word3 ; 2000: @end example 2001: 2002: creates a word called @code{name}, that, upon execution, executes 2003: @code{word1 word2 word3}. @code{name} is a @dfn{(colon) definition}. 2004: 2005: The explanation above is somewhat superficial. @xref{Interpretation and 2006: Compilation Semantics} for an in-depth discussion of some of the issues 2007: involved. 2008: 2009: doc-: 2010: doc-; 2011: 2012: @node User-defined Defining Words, Supplying names, Colon Definitions, Defining Words 2013: @subsection User-defined Defining Words 2014: 2015: You can create new defining words simply by wrapping defining-time code 2016: around existing defining words and putting the sequence in a colon 2017: definition. 2018: 2019: If you want the words defined with your defining words to behave 2020: differently from words defined with standard defining words, you can 2021: write your defining word like this: 2022: 2023: @example 2024: : def-word ( "name" -- ) 2025: Create @var{code1} 2026: DOES> ( ... -- ... ) 2027: @var{code2} ; 2028: 2029: def-word name 2030: @end example 2031: 2032: Technically, this fragment defines a defining word @code{def-word}, and 2033: a word @code{name}; when you execute @code{name}, the address of the 2034: body of @code{name} is put on the data stack and @var{code2} is executed 2035: (the address of the body of @code{name} is the address @code{HERE} 2036: returns immediately after the @code{CREATE}). 2037: 2038: In other words, if you make the following definitions: 2039: 2040: @example 2041: : def-word1 ( "name" -- ) 2042: Create @var{code1} ; 2043: 2044: : action1 ( ... -- ... ) 2045: @var{code2} ; 2046: 2047: def-word name1 2048: @end example 2049: 2050: Using @code{name1 action1} is equivalent to using @code{name}. 2051: 2052: E.g., you can implement @code{Constant} in this way: 2053: 2054: @example 2055: : constant ( w "name" -- ) 2056: create , 2057: DOES> ( -- w ) 2058: @@ ; 2059: @end example 2060: 2061: When you create a constant with @code{5 constant five}, first a new word 2062: @code{five} is created, then the value 5 is laid down in the body of 2063: @code{five} with @code{,}. When @code{five} is invoked, the address of 2064: the body is put on the stack, and @code{@@} retrieves the value 5. 2065: 2066: In the example above the stack comment after the @code{DOES>} specifies 2067: the stack effect of the defined words, not the stack effect of the 2068: following code (the following code expects the address of the body on 2069: the top of stack, which is not reflected in the stack comment). This is 2070: the convention that I use and recommend (it clashes a bit with using 2071: locals declarations for stack effect specification, though). 2072: 2073: @subsubsection Applications of @code{CREATE..DOES>} 2074: 2075: You may wonder how to use this feature. Here are some usage patterns: 2076: 2077: When you see a sequence of code occurring several times, and you can 2078: identify a meaning, you will factor it out as a colon definition. When 2079: you see similar colon definitions, you can factor them using 2080: @code{CREATE..DOES>}. E.g., an assembler usually defines several words 2081: that look very similar: 2082: @example 2083: : ori, ( reg-taget reg-source n -- ) 2084: 0 asm-reg-reg-imm ; 2085: : andi, ( reg-taget reg-source n -- ) 2086: 1 asm-reg-reg-imm ; 2087: @end example 2088: 2089: This could be factored with: 2090: @example 2091: : reg-reg-imm ( op-code -- ) 2092: create , 2093: DOES> ( reg-taget reg-source n -- ) 2094: @@ asm-reg-reg-imm ; 2095: 2096: 0 reg-reg-imm ori, 2097: 1 reg-reg-imm andi, 2098: @end example 2099: 2100: Another view of @code{CREATE..DOES>} is to consider it as a crude way to 2101: supply a part of the parameters for a word (known as @dfn{currying} in 2102: the functional language community). E.g., @code{+} needs two 2103: parameters. Creating versions of @code{+} with one parameter fixed can 2104: be done like this: 2105: @example 2106: : curry+ ( n1 -- ) 2107: create , 2108: DOES> ( n2 -- n1+n2 ) 2109: @@ + ; 2110: 2111: 3 curry+ 3+ 2112: -2 curry+ 2- 2113: @end example 2114: 2115: @subsubsection The gory details of @code{CREATE..DOES>} 2116: 2117: doc-does> 2118: 2119: This means that you need not use @code{CREATE} and @code{DOES>} in the 2120: same definition; E.g., you can put the @code{DOES>}-part in a separate 2121: definition. This allows us to, e.g., select among different DOES>-parts: 2122: @example 2123: : does1 2124: DOES> ( ... -- ... ) 2125: ... ; 2126: 2127: : does2 2128: DOES> ( ... -- ... ) 2129: ... ; 2130: 2131: : def-word ( ... -- ... ) 2132: create ... 2133: IF 2134: does1 2135: ELSE 2136: does2 2137: ENDIF ; 2138: @end example 2139: 2140: In a standard program you can apply a @code{DOES>}-part only if the last 2141: word was defined with @code{CREATE}. In Gforth, the @code{DOES>}-part 2142: will override the behaviour of the last word defined in any case. In a 2143: standard program, you can use @code{DOES>} only in a colon 2144: definition. In Gforth, you can also use it in interpretation state, in a 2145: kind of one-shot mode: 2146: @example 2147: CREATE name ( ... -- ... ) 2148: @var{initialization} 2149: DOES> 2150: @var{code} ; 2151: @end example 2152: This is equivalwent to the standard 2153: @example 2154: :noname 2155: DOES> 2156: @var{code} ; 2157: CREATE name EXECUTE ( ... -- ... ) 2158: @var{initialization} 2159: @end example 2160: 2161: You can get the address of the body of a word with 2162: 2163: doc->body 2164: 2165: @node Supplying names, Interpretation and Compilation Semantics, User-defined Defining Words, Defining Words 2166: @subsection Supplying names for the defined words 2167: 2168: By default, defining words take the names for the defined words from the 2169: input stream. Sometimes you want to supply the name from a string. You 2170: can do this with 2171: 2172: doc-nextname 2173: 2174: E.g., 2175: 2176: @example 2177: s" foo" nextname create 2178: @end example 2179: is equivalent to 2180: @example 2181: create foo 2182: @end example 2183: 2184: Sometimes you want to define a word without a name. You can do this with 2185: 2186: doc-noname 2187: 2188: To make any use of the newly defined word, you need its execution 2189: token. You can get it with 2190: 2191: doc-lastxt 2192: 2193: E.g., you can initialize a deferred word with an anonymous colon 2194: definition: 2195: @example 2196: Defer deferred 2197: noname : ( ... -- ... ) 2198: ... ; 2199: lastxt IS deferred 2200: @end example 2201: 2202: @code{lastxt} also works when the last word was not defined as 2203: @code{noname}. 2204: 2205: The standard has also recognized the need for anonymous words and 2206: provides 2207: 2208: doc-:noname 2209: 2210: This leaves the execution token for the word on the stack after the 2211: closing @code{;}. You can rewrite the last example with @code{:noname}: 2212: @example 2213: Defer deferred 2214: :noname ( ... -- ... ) 2215: ... ; 2216: IS deferred 2217: @end example 2218: 2219: @node Interpretation and Compilation Semantics, , Supplying names, Defining Words 2220: @subsection Interpretation and Compilation Semantics 2221: 2222: The @dfn{interpretation semantics} of a word are what the text 2223: interpreter does when it encounters the word in interpret state. It also 2224: appears in some other contexts, e.g., the execution token returned by 2225: @code{' @var{word}} identifies the interpretation semantics of 2226: @var{word} (in other words, @code{' @var{word} execute} is equivalent to 2227: interpret-state text interpretation of @code{@var{word}}). 2228: 2229: The @dfn{compilation semantics} of a word are what the text interpreter 2230: does when it encounters the word in compile state. It also appears in 2231: other contexts, e.g, @code{POSTPONE @var{word}} compiles@footnote{In 2232: standard terminology, ``appends to the current definition''.} the 2233: compilation semantics of @var{word}. 2234: 2235: The standard also talks about @dfn{execution semantics}. They are used 2236: only for defining the interpretation and compilation semantics of many 2237: words. By default, the interpretation semantics of a word are to 2238: @code{execute} its execution semantics, and the compilation semantics of 2239: a word are to @code{compile,} its execution semantics.@footnote{In 2240: standard terminology: The default interpretation semantics are its 2241: execution semantics; the default compilation semantics are to append its 2242: execution semantics to the execution semantics of the current 2243: definition.} 2244: 2245: You can change the compilation semantics into @code{execute}ing the 2246: execution semantics with 2247: 2248: doc-immediate 2249: 2250: You can remove the interpretation semantics of a word with 2251: 2252: doc-compile-only 2253: doc-restrict 2254: 2255: Note that ticking (@code{'}) compile-only words gives an error 2256: (``Interpreting a compile-only word''). 2257: 2258: Gforth also allows you to define words with arbitrary combinations of 2259: interpretation and compilation semantics. 2260: 2261: doc-interpret/compile: 2262: 2263: This feature was introduced for implementing @code{TO} and @code{S"}. I 2264: recommend that you do not define such words, as cute as they may be: 2265: they make it hard to get at both parts of the word in some contexts. 2266: E.g., assume you want to get an execution token for the compilation 2267: part. Instead, define two words, one that embodies the interpretation 2268: part, and one that embodies the compilation part. 2269: 2270: There is, however, a potentially useful application of this feature: 2271: Providing differing implementations for the default semantics. While 2272: this introduces redundancy and is therefore usually a bad idea, a 2273: performance improvement may be worth the trouble. E.g., consider the 2274: word @code{foobar}: 2275: 2276: @example 2277: : foobar 2278: foo bar ; 2279: @end example 2280: 2281: Let us assume that @code{foobar} is called so frequently that the 2282: calling overhead would take a significant amount of the run-time. We can 2283: optimize it with @code{interpret/compile:}: 2284: 2285: @example 2286: :noname 2287: foo bar ; 2288: :noname 2289: POSTPONE foo POSTPONE bar ; 2290: interpret/compile: foobar 2291: @end example 2292: 2293: This definition has the same interpretation semantics and essentially 2294: the same compilation semantics as the simple definition of 2295: @code{foobar}, but the implementation of the compilation semantics is 2296: more efficient with respect to run-time. 2297: 2298: Some people try to use state-smart words to emulate the feature provided 2299: by @code{interpret/compile:} (words are state-smart if they check 2300: @code{STATE} during execution). E.g., they would try to code 2301: @code{foobar} like this: 2302: 2303: @example 2304: : foobar 2305: STATE @@ 2306: IF ( compilation state ) 2307: POSTPONE foo POSTPONE bar 2308: ELSE 2309: foo bar 2310: ENDIF ; immediate 2311: @end example 2312: 2313: While this works if @code{foobar} is processed only by the text 2314: interpreter, it does not work in other contexts (like @code{'} or 2315: @code{POSTPONE}). E.g., @code{' foobar} will produce an execution token 2316: for a state-smart word, not for the interpretation semantics of the 2317: original @code{foobar}; when you execute this execution token (directly 2318: with @code{EXECUTE} or indirectly through @code{COMPILE,}) in compile 2319: state, the result will not be what you expected (i.e., it will not 2320: perform @code{foo bar}). State-smart words are a bad idea. Simply don't 2321: write them! 2322: 2323: It is also possible to write defining words that define words with 2324: arbitrary combinations of interpretation and compilation semantics (or, 2325: preferably, arbitrary combinations of implementations of the default 2326: semantics). In general, this looks like: 2327: 2328: @example 2329: : def-word 2330: create-interpret/compile 2331: @var{code1} 2332: interpretation> 2333: @var{code2} 2334: <interpretation 2335: compilation> 2336: @var{code3} 2337: <compilation ; 2338: @end example 2339: 2340: For a @var{word} defined with @code{def-word}, the interpretation 2341: semantics are to push the address of the body of @var{word} and perform 2342: @var{code2}, and the compilation semantics are to push the address of 2343: the body of @var{word} and perform @var{code3}. E.g., @code{constant} 2344: can also be defined like this: 2345: 2346: @example 2347: : constant ( n "name" -- ) 2348: create-interpret/compile 2349: , 2350: interpretation> ( -- n ) 2351: @@ 2352: <interpretation 2353: compilation> ( compilation. -- ; run-time. -- n ) 2354: @@ postpone literal 2355: <compilation ; 2356: @end example 2357: 2358: doc-create-interpret/compile 2359: doc-interpretation> 2360: doc-<interpretation 2361: doc-compilation> 2362: doc-<compilation 2363: 2364: Note that words defined with @code{interpret/compile:} and 2365: @code{create-interpret/compile} have an extended header structure that 2366: differs from other words; however, unless you try to access them with 2367: plain address arithmetic, you should not notice this. Words for 2368: accessing the header structure usually know how to deal with this; e.g., 2369: @code{' word >body} also gives you the body of a word created with 2370: @code{create-interpret/compile}. 2371: 2372: @node Tokens for Words, Wordlists, Defining Words, Words 2373: @section Tokens for Words 2374: 2375: This chapter describes the creation and use of tokens that represent 2376: words on the stack (and in data space). 2377: 2378: Named words have interpretation and compilation semantics. Unnamed words 2379: just have execution semantics. 2380: 2381: An @dfn{execution token} represents the execution semantics of an 2382: unnamed word. An execution token occupies one cell. As explained in 2383: section @ref{Supplying names}, the execution token of the last words 2384: defined can be produced with 2385: 2386: short-lastxt 2387: 2388: You can perform the semantics represented by an execution token with 2389: doc-execute 2390: You can compile the word with 2391: doc-compile, 2392: 2393: In Gforth, the abstract data type @emph{execution token} is implemented 2394: as CFA (code field address). 2395: 2396: The interpretation semantics of a named word are also represented by an 2397: execution token. You can get it with 2398: 2399: doc-['] 2400: doc-' 2401: 2402: For literals, you use @code{'} in interpreted code and @code{[']} in 2403: compiled code. Gforth's @code{'} and @code{[']} behave somewhat unusual 2404: by complaining about compile-only words. To get an execution token for a 2405: compiling word @var{X}, use @code{COMP' @var{X} drop} or @code{[COMP'] 2406: @var{X} drop}. 2407: 2408: The compilation semantics are represented by a @dfn{compilation token} 2409: consisting of two cells: @var{w xt}. The top cell @var{xt} is an 2410: execution token. The compilation semantics represented by the 2411: compilation token can be performed with @code{execute}, which consumes 2412: the whole compilation token, with an additional stack effect determined 2413: by the represented compilation semantics. 2414: 2415: doc-[comp'] 2416: doc-comp' 2417: 2418: You can compile the compilation semantics with @code{postpone,}. I.e., 2419: @code{COMP' @var{word} POSTPONE,} is equivalent to @code{POSTPONE 2420: @var{word}}. 2421: 2422: doc-postpone, 2423: 2424: At present, the @var{w} part of a compilation token is an execution 2425: token, and the @var{xt} part represents either @code{execute} or 2426: @code{compile,}. However, don't rely on that kowledge, unless necessary; 2427: we may introduce unusual compilation tokens in the future (e.g., 2428: compilation tokens representing the compilation semantics of literals). 2429: 2430: Named words are also represented by the @dfn{name token}. The abstract 2431: data type @emph{name token} is implemented as NFA (name field address). 2432: 2433: doc-find-name 2434: doc-name>int 2435: doc-name?int 2436: doc-name>comp 2437: doc-name>string 2438: 2439: @node Wordlists, Files, Tokens for Words, Words 2440: @section Wordlists 2441: 2442: @node Files, Blocks, Wordlists, Words 2443: @section Files 2444: 2445: @node Blocks, Other I/O, Files, Words 2446: @section Blocks 2447: 2448: @node Other I/O, Programming Tools, Blocks, Words 2449: @section Other I/O 2450: 2451: @node Programming Tools, Assembler and Code words, Other I/O, Words 2452: @section Programming Tools 2453: 2454: @menu 2455: * Debugging:: Simple and quick. 2456: * Assertions:: Making your programs self-checking. 2457: @end menu 2458: 2459: @node Debugging, Assertions, Programming Tools, Programming Tools 2460: @subsection Debugging 2461: 2462: The simple debugging aids provided in @file{debugging.fs} 2463: are meant to support a different style of debugging than the 2464: tracing/stepping debuggers used in languages with long turn-around 2465: times. 2466: 2467: A much better (faster) way in fast-compilig languages is to add 2468: printing code at well-selected places, let the program run, look at 2469: the output, see where things went wrong, add more printing code, etc., 2470: until the bug is found. 2471: 2472: The word @code{~~} is easy to insert. It just prints debugging 2473: information (by default the source location and the stack contents). It 2474: is also easy to remove (@kbd{C-x ~} in the Emacs Forth mode to 2475: query-replace them with nothing). The deferred words 2476: @code{printdebugdata} and @code{printdebugline} control the output of 2477: @code{~~}. The default source location output format works well with 2478: Emacs' compilation mode, so you can step through the program at the 2479: source level using @kbd{C-x `} (the advantage over a stepping debugger 2480: is that you can step in any direction and you know where the crash has 2481: happened or where the strange data has occurred). 2482: 2483: Note that the default actions clobber the contents of the pictured 2484: numeric output string, so you should not use @code{~~}, e.g., between 2485: @code{<#} and @code{#>}. 2486: 2487: doc-~~ 2488: doc-printdebugdata 2489: doc-printdebugline 2490: 2491: @node Assertions, , Debugging, Programming Tools 2492: @subsection Assertions 2493: 2494: It is a good idea to make your programs self-checking, in particular, if 2495: you use an assumption (e.g., that a certain field of a data structure is 2496: never zero) that may become wrong during maintenance. Gforth supports 2497: assertions for this purpose. They are used like this: 2498: 2499: @example 2500: assert( @var{flag} ) 2501: @end example 2502: 2503: The code between @code{assert(} and @code{)} should compute a flag, that 2504: should be true if everything is alright and false otherwise. It should 2505: not change anything else on the stack. The overall stack effect of the 2506: assertion is @code{( -- )}. E.g. 2507: 2508: @example 2509: assert( 1 1 + 2 = ) \ what we learn in school 2510: assert( dup 0<> ) \ assert that the top of stack is not zero 2511: assert( false ) \ this code should not be reached 2512: @end example 2513: 2514: The need for assertions is different at different times. During 2515: debugging, we want more checking, in production we sometimes care more 2516: for speed. Therefore, assertions can be turned off, i.e., the assertion 2517: becomes a comment. Depending on the importance of an assertion and the 2518: time it takes to check it, you may want to turn off some assertions and 2519: keep others turned on. Gforth provides several levels of assertions for 2520: this purpose: 2521: 2522: doc-assert0( 2523: doc-assert1( 2524: doc-assert2( 2525: doc-assert3( 2526: doc-assert( 2527: doc-) 2528: 2529: @code{Assert(} is the same as @code{assert1(}. The variable 2530: @code{assert-level} specifies the highest assertions that are turned 2531: on. I.e., at the default @code{assert-level} of one, @code{assert0(} and 2532: @code{assert1(} assertions perform checking, while @code{assert2(} and 2533: @code{assert3(} assertions are treated as comments. 2534: 2535: Note that the @code{assert-level} is evaluated at compile-time, not at 2536: run-time. I.e., you cannot turn assertions on or off at run-time, you 2537: have to set the @code{assert-level} appropriately before compiling a 2538: piece of code. You can compile several pieces of code at several 2539: @code{assert-level}s (e.g., a trusted library at level 1 and newly 2540: written code at level 3). 2541: 2542: doc-assert-level 2543: 2544: If an assertion fails, a message compatible with Emacs' compilation mode 2545: is produced and the execution is aborted (currently with @code{ABORT"}. 2546: If there is interest, we will introduce a special throw code. But if you 2547: intend to @code{catch} a specific condition, using @code{throw} is 2548: probably more appropriate than an assertion). 2549: 2550: @node Assembler and Code words, Threading Words, Programming Tools, Words 2551: @section Assembler and Code words 2552: 2553: Gforth provides some words for defining primitives (words written in 2554: machine code), and for defining the the machine-code equivalent of 2555: @code{DOES>}-based defining words. However, the machine-independent 2556: nature of Gforth poses a few problems: First of all, Gforth runs on 2557: several architectures, so it can provide no standard assembler. What's 2558: worse is that the register allocation not only depends on the processor, 2559: but also on the @code{gcc} version and options used. 2560: 2561: The words that Gforth offers encapsulate some system dependences (e.g., the 2562: header structure), so a system-independent assembler may be used in 2563: Gforth. If you do not have an assembler, you can compile machine code 2564: directly with @code{,} and @code{c,}. 2565: 2566: doc-assembler 2567: doc-code 2568: doc-end-code 2569: doc-;code 2570: doc-flush-icache 2571: 2572: If @code{flush-icache} does not work correctly, @code{code} words 2573: etc. will not work (reliably), either. 2574: 2575: These words are rarely used. Therefore they reside in @code{code.fs}, 2576: which is usually not loaded (except @code{flush-icache}, which is always 2577: present). You can load them with @code{require code.fs}. 2578: 2579: In the assembly code you will want to refer to the inner interpreter's 2580: registers (e.g., the data stack pointer) and you may want to use other 2581: registers for temporary storage. Unfortunately, the register allocation 2582: is installation-dependent. 2583: 2584: The easiest solution is to use explicit register declarations 2585: (@pxref{Explicit Reg Vars, , Variables in Specified Registers, gcc.info, 2586: GNU C Manual}) for all of the inner interpreter's registers: You have to 2587: compile Gforth with @code{-DFORCE_REG} (configure option 2588: @code{--enable-force-reg}) and the appropriate declarations must be 2589: present in the @code{machine.h} file (see @code{mips.h} for an example; 2590: you can find a full list of all declarable register symbols with 2591: @code{grep register engine.c}). If you give explicit registers to all 2592: variables that are declared at the beginning of @code{engine()}, you 2593: should be able to use the other caller-saved registers for temporary 2594: storage. Alternatively, you can use the @code{gcc} option 2595: @code{-ffixed-REG} (@pxref{Code Gen Options, , Options for Code 2596: Generation Conventions, gcc.info, GNU C Manual}) to reserve a register 2597: (however, this restriction on register allocation may slow Gforth 2598: significantly). 2599: 2600: If this solution is not viable (e.g., because @code{gcc} does not allow 2601: you to explicitly declare all the registers you need), you have to find 2602: out by looking at the code where the inner interpreter's registers 2603: reside and which registers can be used for temporary storage. You can 2604: get an assembly listing of the engine's code with @code{make engine.s}. 2605: 2606: In any case, it is good practice to abstract your assembly code from the 2607: actual register allocation. E.g., if the data stack pointer resides in 2608: register @code{$17}, create an alias for this register called @code{sp}, 2609: and use that in your assembly code. 2610: 2611: Another option for implementing normal and defining words efficiently 2612: is: adding the wanted functionality to the source of Gforth. For normal 2613: words you just have to edit @file{primitives} (@pxref{Automatic 2614: Generation}), defining words (equivalent to @code{;CODE} words, for fast 2615: defined words) may require changes in @file{engine.c}, @file{kernal.fs}, 2616: @file{prims2x.fs}, and possibly @file{cross.fs}. 2617: 2618: 2619: @node Threading Words, , Assembler and Code words, Words 2620: @section Threading Words 2621: 2622: These words provide access to code addresses and other threading stuff 2623: in Gforth (and, possibly, other interpretive Forths). It more or less 2624: abstracts away the differences between direct and indirect threading 2625: (and, for direct threading, the machine dependences). However, at 2626: present this wordset is still inclomplete. It is also pretty low-level; 2627: some day it will hopefully be made unnecessary by an internals words set 2628: that abstracts implementation details away completely. 2629: 2630: doc->code-address 2631: doc->does-code 2632: doc-code-address! 2633: doc-does-code! 2634: doc-does-handler! 2635: doc-/does-handler 2636: 2637: The code addresses produced by various defining words are produced by 2638: the following words: 2639: 2640: doc-docol: 2641: doc-docon: 2642: doc-dovar: 2643: doc-douser: 2644: doc-dodefer: 2645: doc-dofield: 2646: 2647: You can recognize words defined by a @code{CREATE}...@code{DOES>} word 2648: with @code{>DOES-CODE}. If the word was defined in that way, the value 2649: returned is different from 0 and identifies the @code{DOES>} used by the 2650: defining word. 2651: 2652: @node Tools, ANS conformance, Words, Top 2653: @chapter Tools 2654: 2655: @menu 2656: * ANS Report:: Report the words used, sorted by wordset 2657: @end menu 2658: 2659: See also @ref{Emacs and Gforth}. 2660: 2661: @node ANS Report, , Tools, Tools 2662: @section @file{ans-report.fs}: Report the words used, sorted by wordset 2663: 2664: If you want to label a Forth program as ANS Forth Program, you must 2665: document which wordsets the program uses; for extension wordsets, it is 2666: helpful to list the words the program requires from these wordsets 2667: (because Forth systems are allowed to provide only some words of them). 2668: 2669: The @file{ans-report.fs} tool makes it easy for you to determine which 2670: words from which wordset and which non-ANS words your application 2671: uses. You simply have to include @file{ans-report.fs} before loading the 2672: program you want to check. After loading your program, you can get the 2673: report with @code{print-ans-report}. A typical use is to run this as 2674: batch job like this: 2675: @example 2676: gforth ans-report.fs myprog.fs -e "print-ans-report bye" 2677: @end example 2678: 2679: The output looks like this (for @file{compat/control.fs}): 2680: @example 2681: The program uses the following words 2682: from CORE : 2683: : POSTPONE THEN ; immediate ?dup IF 0= 2684: from BLOCK-EXT : 2685: \ 2686: from FILE : 2687: ( 2688: @end example 2689: 2690: @subsection Caveats 2691: 2692: Note that @file{ans-report.fs} just checks which words are used, not whether 2693: they are used in an ANS Forth conforming way! 2694: 2695: Some words are defined in several wordsets in the 2696: standard. @file{ans-report.fs} reports them for only one of the 2697: wordsets, and not necessarily the one you expect. It depends on usage 2698: which wordset is the right one to specify. E.g., if you only use the 2699: compilation semantics of @code{S"}, it is a Core word; if you also use 2700: its interpretation semantics, it is a File word. 2701: 2702: 2703: @node ANS conformance, Model, Tools, Top 2704: @chapter ANS conformance 2705: 2706: To the best of our knowledge, Gforth is an 2707: 2708: ANS Forth System 2709: @itemize @bullet 2710: @item providing the Core Extensions word set 2711: @item providing the Block word set 2712: @item providing the Block Extensions word set 2713: @item providing the Double-Number word set 2714: @item providing the Double-Number Extensions word set 2715: @item providing the Exception word set 2716: @item providing the Exception Extensions word set 2717: @item providing the Facility word set 2718: @item providing @code{MS} and @code{TIME&DATE} from the Facility Extensions word set 2719: @item providing the File Access word set 2720: @item providing the File Access Extensions word set 2721: @item providing the Floating-Point word set 2722: @item providing the Floating-Point Extensions word set 2723: @item providing the Locals word set 2724: @item providing the Locals Extensions word set 2725: @item providing the Memory-Allocation word set 2726: @item providing the Memory-Allocation Extensions word set (that one's easy) 2727: @item providing the Programming-Tools word set 2728: @item providing @code{;CODE}, @code{AHEAD}, @code{ASSEMBLER}, @code{BYE}, @code{CODE}, @code{CS-PICK}, @code{CS-ROLL}, @code{STATE}, @code{[ELSE]}, @code{[IF]}, @code{[THEN]} from the Programming-Tools Extensions word set 2729: @item providing the Search-Order word set 2730: @item providing the Search-Order Extensions word set 2731: @item providing the String word set 2732: @item providing the String Extensions word set (another easy one) 2733: @end itemize 2734: 2735: In addition, ANS Forth systems are required to document certain 2736: implementation choices. This chapter tries to meet these 2737: requirements. In many cases it gives a way to ask the system for the 2738: information instead of providing the information directly, in 2739: particular, if the information depends on the processor, the operating 2740: system or the installation options chosen, or if they are likely to 2741: change during the maintenance of Gforth. 2742: 2743: @comment The framework for the rest has been taken from pfe. 2744: 2745: @menu 2746: * The Core Words:: 2747: * The optional Block word set:: 2748: * The optional Double Number word set:: 2749: * The optional Exception word set:: 2750: * The optional Facility word set:: 2751: * The optional File-Access word set:: 2752: * The optional Floating-Point word set:: 2753: * The optional Locals word set:: 2754: * The optional Memory-Allocation word set:: 2755: * The optional Programming-Tools word set:: 2756: * The optional Search-Order word set:: 2757: @end menu 2758: 2759: 2760: @c ===================================================================== 2761: @node The Core Words, The optional Block word set, ANS conformance, ANS conformance 2762: @comment node-name, next, previous, up 2763: @section The Core Words 2764: @c ===================================================================== 2765: 2766: @menu 2767: * core-idef:: Implementation Defined Options 2768: * core-ambcond:: Ambiguous Conditions 2769: * core-other:: Other System Documentation 2770: @end menu 2771: 2772: @c --------------------------------------------------------------------- 2773: @node core-idef, core-ambcond, The Core Words, The Core Words 2774: @subsection Implementation Defined Options 2775: @c --------------------------------------------------------------------- 2776: 2777: @table @i 2778: 2779: @item (Cell) aligned addresses: 2780: processor-dependent. Gforth's alignment words perform natural alignment 2781: (e.g., an address aligned for a datum of size 8 is divisible by 2782: 8). Unaligned accesses usually result in a @code{-23 THROW}. 2783: 2784: @item @code{EMIT} and non-graphic characters: 2785: The character is output using the C library function (actually, macro) 2786: @code{putc}. 2787: 2788: @item character editing of @code{ACCEPT} and @code{EXPECT}: 2789: This is modeled on the GNU readline library (@pxref{Readline 2790: Interaction, , Command Line Editing, readline, The GNU Readline 2791: Library}) with Emacs-like key bindings. @kbd{Tab} deviates a little by 2792: producing a full word completion every time you type it (instead of 2793: producing the common prefix of all completions). 2794: 2795: @item character set: 2796: The character set of your computer and display device. Gforth is 2797: 8-bit-clean (but some other component in your system may make trouble). 2798: 2799: @item Character-aligned address requirements: 2800: installation-dependent. Currently a character is represented by a C 2801: @code{unsigned char}; in the future we might switch to @code{wchar_t} 2802: (Comments on that requested). 2803: 2804: @item character-set extensions and matching of names: 2805: Any character except the ASCII NUL charcter can be used in a 2806: name. Matching is case-insensitive (except in @code{TABLE}s. The 2807: matching is performed using the C function @code{strncasecmp}, whose 2808: function is probably influenced by the locale. E.g., the @code{C} locale 2809: does not know about accents and umlauts, so they are matched 2810: case-sensitively in that locale. For portability reasons it is best to 2811: write programs such that they work in the @code{C} locale. Then one can 2812: use libraries written by a Polish programmer (who might use words 2813: containing ISO Latin-2 encoded characters) and by a French programmer 2814: (ISO Latin-1) in the same program (of course, @code{WORDS} will produce 2815: funny results for some of the words (which ones, depends on the font you 2816: are using)). Also, the locale you prefer may not be available in other 2817: operating systems. Hopefully, Unicode will solve these problems one day. 2818: 2819: @item conditions under which control characters match a space delimiter: 2820: If @code{WORD} is called with the space character as a delimiter, all 2821: white-space characters (as identified by the C macro @code{isspace()}) 2822: are delimiters. @code{PARSE}, on the other hand, treats space like other 2823: delimiters. @code{PARSE-WORD} treats space like @code{WORD}, but behaves 2824: like @code{PARSE} otherwise. @code{(NAME)}, which is used by the outer 2825: interpreter (aka text interpreter) by default, treats all white-space 2826: characters as delimiters. 2827: 2828: @item format of the control flow stack: 2829: The data stack is used as control flow stack. The size of a control flow 2830: stack item in cells is given by the constant @code{cs-item-size}. At the 2831: time of this writing, an item consists of a (pointer to a) locals list 2832: (third), an address in the code (second), and a tag for identifying the 2833: item (TOS). The following tags are used: @code{defstart}, 2834: @code{live-orig}, @code{dead-orig}, @code{dest}, @code{do-dest}, 2835: @code{scopestart}. 2836: 2837: @item conversion of digits > 35 2838: The characters @code{[\]^_'} are the digits with the decimal value 2839: 36@minus{}41. There is no way to input many of the larger digits. 2840: 2841: @item display after input terminates in @code{ACCEPT} and @code{EXPECT}: 2842: The cursor is moved to the end of the entered string. If the input is 2843: terminated using the @kbd{Return} key, a space is typed. 2844: 2845: @item exception abort sequence of @code{ABORT"}: 2846: The error string is stored into the variable @code{"error} and a 2847: @code{-2 throw} is performed. 2848: 2849: @item input line terminator: 2850: For interactive input, @kbd{C-m} (CR) and @kbd{C-j} (LF) terminate 2851: lines. One of these characters is typically produced when you type the 2852: @kbd{Enter} or @kbd{Return} key. 2853: 2854: @item maximum size of a counted string: 2855: @code{s" /counted-string" environment? drop .}. Currently 255 characters 2856: on all ports, but this may change. 2857: 2858: @item maximum size of a parsed string: 2859: Given by the constant @code{/line}. Currently 255 characters. 2860: 2861: @item maximum size of a definition name, in characters: 2862: 31 2863: 2864: @item maximum string length for @code{ENVIRONMENT?}, in characters: 2865: 31 2866: 2867: @item method of selecting the user input device: 2868: The user input device is the standard input. There is currently no way to 2869: change it from within Gforth. However, the input can typically be 2870: redirected in the command line that starts Gforth. 2871: 2872: @item method of selecting the user output device: 2873: @code{EMIT} and @code{TYPE} output to the file-id stored in the value 2874: @code{outfile-id} (@code{stdout} by default). Gforth uses buffered 2875: output, so output on a terminal does not become visible before the next 2876: newline or buffer overflow. Output on non-terminals is invisible until 2877: the buffer overflows. 2878: 2879: @item methods of dictionary compilation: 2880: What are we expected to document here? 2881: 2882: @item number of bits in one address unit: 2883: @code{s" address-units-bits" environment? drop .}. 8 in all current 2884: ports. 2885: 2886: @item number representation and arithmetic: 2887: Processor-dependent. Binary two's complement on all current ports. 2888: 2889: @item ranges for integer types: 2890: Installation-dependent. Make environmental queries for @code{MAX-N}, 2891: @code{MAX-U}, @code{MAX-D} and @code{MAX-UD}. The lower bounds for 2892: unsigned (and positive) types is 0. The lower bound for signed types on 2893: two's complement and one's complement machines machines can be computed 2894: by adding 1 to the upper bound. 2895: 2896: @item read-only data space regions: 2897: The whole Forth data space is writable. 2898: 2899: @item size of buffer at @code{WORD}: 2900: @code{PAD HERE - .}. 104 characters on 32-bit machines. The buffer is 2901: shared with the pictured numeric output string. If overwriting 2902: @code{PAD} is acceptable, it is as large as the remaining dictionary 2903: space, although only as much can be sensibly used as fits in a counted 2904: string. 2905: 2906: @item size of one cell in address units: 2907: @code{1 cells .}. 2908: 2909: @item size of one character in address units: 2910: @code{1 chars .}. 1 on all current ports. 2911: 2912: @item size of the keyboard terminal buffer: 2913: Varies. You can determine the size at a specific time using @code{lp@@ 2914: tib - .}. It is shared with the locals stack and TIBs of files that 2915: include the current file. You can change the amount of space for TIBs 2916: and locals stack at Gforth startup with the command line option 2917: @code{-l}. 2918: 2919: @item size of the pictured numeric output buffer: 2920: @code{PAD HERE - .}. 104 characters on 32-bit machines. The buffer is 2921: shared with @code{WORD}. 2922: 2923: @item size of the scratch area returned by @code{PAD}: 2924: The remainder of dictionary space. You can even use the unused part of 2925: the data stack space. The current size can be computed with @code{sp@@ 2926: pad - .}. 2927: 2928: @item system case-sensitivity characteristics: 2929: Dictionary searches are case insensitive (except in 2930: @code{TABLE}s). However, as explained above under @i{character-set 2931: extensions}, the matching for non-ASCII characters is determined by the 2932: locale you are using. In the default @code{C} locale all non-ASCII 2933: characters are matched case-sensitively. 2934: 2935: @item system prompt: 2936: @code{ ok} in interpret state, @code{ compiled} in compile state. 2937: 2938: @item division rounding: 2939: installation dependent. @code{s" floored" environment? drop .}. We leave 2940: the choice to @code{gcc} (what to use for @code{/}) and to you (whether to use 2941: @code{fm/mod}, @code{sm/rem} or simply @code{/}). 2942: 2943: @item values of @code{STATE} when true: 2944: -1. 2945: 2946: @item values returned after arithmetic overflow: 2947: On two's complement machines, arithmetic is performed modulo 2948: 2**bits-per-cell for single arithmetic and 4**bits-per-cell for double 2949: arithmetic (with appropriate mapping for signed types). Division by zero 2950: typically results in a @code{-55 throw} (Floating-point unidentified 2951: fault), although a @code{-10 throw} (divide by zero) would be more 2952: appropriate. 2953: 2954: @item whether the current definition can be found after @t{DOES>}: 2955: No. 2956: 2957: @end table 2958: 2959: @c --------------------------------------------------------------------- 2960: @node core-ambcond, core-other, core-idef, The Core Words 2961: @subsection Ambiguous conditions 2962: @c --------------------------------------------------------------------- 2963: 2964: @table @i 2965: 2966: @item a name is neither a word nor a number: 2967: @code{-13 throw} (Undefined word). Actually, @code{-13 bounce}, which 2968: preserves the data and FP stack, so you don't lose more work than 2969: necessary. 2970: 2971: @item a definition name exceeds the maximum length allowed: 2972: @code{-19 throw} (Word name too long) 2973: 2974: @item addressing a region not inside the various data spaces of the forth system: 2975: The stacks, code space and name space are accessible. Machine code space is 2976: typically readable. Accessing other addresses gives results dependent on 2977: the operating system. On decent systems: @code{-9 throw} (Invalid memory 2978: address). 2979: 2980: @item argument type incompatible with parameter: 2981: This is usually not caught. Some words perform checks, e.g., the control 2982: flow words, and issue a @code{ABORT"} or @code{-12 THROW} (Argument type 2983: mismatch). 2984: 2985: @item attempting to obtain the execution token of a word with undefined execution semantics: 2986: @code{-14 throw} (Interpreting a compile-only word). In some cases, you 2987: get an execution token for @code{compile-only-error} (which performs a 2988: @code{-14 throw} when executed). 2989: 2990: @item dividing by zero: 2991: typically results in a @code{-55 throw} (floating point unidentified 2992: fault), although a @code{-10 throw} (divide by zero) would be more 2993: appropriate. 2994: 2995: @item insufficient data stack or return stack space: 2996: Not checked. This typically results in mysterious illegal memory 2997: accesses, producing @code{-9 throw} (Invalid memory address) or 2998: @code{-23 throw} (Address alignment exception). 2999: 3000: @item insufficient space for loop control parameters: 3001: like other return stack overflows. 3002: 3003: @item insufficient space in the dictionary: 3004: Not checked. Similar results as stack overflows. However, typically the 3005: error appears at a different place when one inserts or removes code. 3006: 3007: @item interpreting a word with undefined interpretation semantics: 3008: For some words, we defined interpretation semantics. For the others: 3009: @code{-14 throw} (Interpreting a compile-only word). 3010: 3011: @item modifying the contents of the input buffer or a string literal: 3012: These are located in writable memory and can be modified. 3013: 3014: @item overflow of the pictured numeric output string: 3015: Not checked. 3016: 3017: @item parsed string overflow: 3018: @code{PARSE} cannot overflow. @code{WORD} does not check for overflow. 3019: 3020: @item producing a result out of range: 3021: On two's complement machines, arithmetic is performed modulo 3022: 2**bits-per-cell for single arithmetic and 4**bits-per-cell for double 3023: arithmetic (with appropriate mapping for signed types). Division by zero 3024: typically results in a @code{-55 throw} (floatingpoint unidentified 3025: fault), although a @code{-10 throw} (divide by zero) would be more 3026: appropriate. @code{convert} and @code{>number} currently overflow 3027: silently. 3028: 3029: @item reading from an empty data or return stack: 3030: The data stack is checked by the outer (aka text) interpreter after 3031: every word executed. If it has underflowed, a @code{-4 throw} (Stack 3032: underflow) is performed. Apart from that, the stacks are not checked and 3033: underflows can result in similar behaviour as overflows (of adjacent 3034: stacks). 3035: 3036: @item unexpected end of the input buffer, resulting in an attempt to use a zero-length string as a name: 3037: @code{Create} and its descendants perform a @code{-16 throw} (Attempt to 3038: use zero-length string as a name). Words like @code{'} probably will not 3039: find what they search. Note that it is possible to create zero-length 3040: names with @code{nextname} (should it not?). 3041: 3042: @item @code{>IN} greater than input buffer: 3043: The next invocation of a parsing word returns a string wih length 0. 3044: 3045: @item @code{RECURSE} appears after @code{DOES>}: 3046: Compiles a recursive call to the defining word, not to the defined word. 3047: 3048: @item argument input source different than current input source for @code{RESTORE-INPUT}: 3049: @code{-12 THROW}. Note that, once an input file is closed (e.g., because 3050: the end of the file was reached), its source-id may be 3051: reused. Therefore, restoring an input source specification referencing a 3052: closed file may lead to unpredictable results instead of a @code{-12 3053: THROW}. 3054: 3055: In the future, Gforth may be able to restore input source specifications 3056: from other than the current input soruce. 3057: 3058: @item data space containing definitions gets de-allocated: 3059: Deallocation with @code{allot} is not checked. This typically resuls in 3060: memory access faults or execution of illegal instructions. 3061: 3062: @item data space read/write with incorrect alignment: 3063: Processor-dependent. Typically results in a @code{-23 throw} (Address 3064: alignment exception). Under Linux on a 486 or later processor with 3065: alignment turned on, incorrect alignment results in a @code{-9 throw} 3066: (Invalid memory address). There are reportedly some processors with 3067: alignment restrictions that do not report them. 3068: 3069: @item data space pointer not properly aligned, @code{,}, @code{C,}: 3070: Like other alignment errors. 3071: 3072: @item less than u+2 stack items (@code{PICK} and @code{ROLL}): 3073: Not checked. May cause an illegal memory access. 3074: 3075: @item loop control parameters not available: 3076: Not checked. The counted loop words simply assume that the top of return 3077: stack items are loop control parameters and behave accordingly. 3078: 3079: @item most recent definition does not have a name (@code{IMMEDIATE}): 3080: @code{abort" last word was headerless"}. 3081: 3082: @item name not defined by @code{VALUE} used by @code{TO}: 3083: @code{-32 throw} (Invalid name argument) (unless name was defined by 3084: @code{CONSTANT}; then it just changes the constant). 3085: 3086: @item name not found (@code{'}, @code{POSTPONE}, @code{[']}, @code{[COMPILE]}): 3087: @code{-13 throw} (Undefined word) 3088: 3089: @item parameters are not of the same type (@code{DO}, @code{?DO}, @code{WITHIN}): 3090: Gforth behaves as if they were of the same type. I.e., you can predict 3091: the behaviour by interpreting all parameters as, e.g., signed. 3092: 3093: @item @code{POSTPONE} or @code{[COMPILE]} applied to @code{TO}: 3094: Assume @code{: X POSTPONE TO ; IMMEDIATE}. @code{X} performs the 3095: compilation semantics of @code{TO}. 3096: 3097: @item String longer than a counted string returned by @code{WORD}: 3098: Not checked. The string will be ok, but the count will, of course, 3099: contain only the least significant bits of the length. 3100: 3101: @item u greater than or equal to the number of bits in a cell (@code{LSHIFT}, @code{RSHIFT}): 3102: Processor-dependent. Typical behaviours are returning 0 and using only 3103: the low bits of the shift count. 3104: 3105: @item word not defined via @code{CREATE}: 3106: @code{>BODY} produces the PFA of the word no matter how it was defined. 3107: 3108: @code{DOES>} changes the execution semantics of the last defined word no 3109: matter how it was defined. E.g., @code{CONSTANT DOES>} is equivalent to 3110: @code{CREATE , DOES>}. 3111: 3112: @item words improperly used outside @code{<#} and @code{#>}: 3113: Not checked. As usual, you can expect memory faults. 3114: 3115: @end table 3116: 3117: 3118: @c --------------------------------------------------------------------- 3119: @node core-other, , core-ambcond, The Core Words 3120: @subsection Other system documentation 3121: @c --------------------------------------------------------------------- 3122: 3123: @table @i 3124: 3125: @item nonstandard words using @code{PAD}: 3126: None. 3127: 3128: @item operator's terminal facilities available: 3129: After processing the command line, Gforth goes into interactive mode, 3130: and you can give commands to Gforth interactively. The actual facilities 3131: available depend on how you invoke Gforth. 3132: 3133: @item program data space available: 3134: @code{sp@@ here - .} gives the space remaining for dictionary and data 3135: stack together. 3136: 3137: @item return stack space available: 3138: By default 16 KBytes. The default can be overridden with the @code{-r} 3139: switch (@pxref{Invocation}) when Gforth starts up. 3140: 3141: @item stack space available: 3142: @code{sp@@ here - .} gives the space remaining for dictionary and data 3143: stack together. 3144: 3145: @item system dictionary space required, in address units: 3146: Type @code{here forthstart - .} after startup. At the time of this 3147: writing, this gives 70108 (bytes) on a 32-bit system. 3148: @end table 3149: 3150: 3151: @c ===================================================================== 3152: @node The optional Block word set, The optional Double Number word set, The Core Words, ANS conformance 3153: @section The optional Block word set 3154: @c ===================================================================== 3155: 3156: @menu 3157: * block-idef:: Implementation Defined Options 3158: * block-ambcond:: Ambiguous Conditions 3159: * block-other:: Other System Documentation 3160: @end menu 3161: 3162: 3163: @c --------------------------------------------------------------------- 3164: @node block-idef, block-ambcond, The optional Block word set, The optional Block word set 3165: @subsection Implementation Defined Options 3166: @c --------------------------------------------------------------------- 3167: 3168: @table @i 3169: 3170: @item the format for display by @code{LIST}: 3171: First the screen number is displayed, then 16 lines of 64 characters, 3172: each line preceded by the line number. 3173: 3174: @item the length of a line affected by @code{\}: 3175: 64 characters. 3176: @end table 3177: 3178: 3179: @c --------------------------------------------------------------------- 3180: @node block-ambcond, block-other, block-idef, The optional Block word set 3181: @subsection Ambiguous conditions 3182: @c --------------------------------------------------------------------- 3183: 3184: @table @i 3185: 3186: @item correct block read was not possible: 3187: Typically results in a @code{throw} of some OS-derived value (between 3188: -512 and -2048). If the blocks file was just not long enough, blanks are 3189: supplied for the missing portion. 3190: 3191: @item I/O exception in block transfer: 3192: Typically results in a @code{throw} of some OS-derived value (between 3193: -512 and -2048). 3194: 3195: @item invalid block number: 3196: @code{-35 throw} (Invalid block number) 3197: 3198: @item a program directly alters the contents of @code{BLK}: 3199: The input stream is switched to that other block, at the same 3200: position. If the storing to @code{BLK} happens when interpreting 3201: non-block input, the system will get quite confused when the block ends. 3202: 3203: @item no current block buffer for @code{UPDATE}: 3204: @code{UPDATE} has no effect. 3205: 3206: @end table 3207: 3208: 3209: @c --------------------------------------------------------------------- 3210: @node block-other, , block-ambcond, The optional Block word set 3211: @subsection Other system documentation 3212: @c --------------------------------------------------------------------- 3213: 3214: @table @i 3215: 3216: @item any restrictions a multiprogramming system places on the use of buffer addresses: 3217: No restrictions (yet). 3218: 3219: @item the number of blocks available for source and data: 3220: depends on your disk space. 3221: 3222: @end table 3223: 3224: 3225: @c ===================================================================== 3226: @node The optional Double Number word set, The optional Exception word set, The optional Block word set, ANS conformance 3227: @section The optional Double Number word set 3228: @c ===================================================================== 3229: 3230: @menu 3231: * double-ambcond:: Ambiguous Conditions 3232: @end menu 3233: 3234: 3235: @c --------------------------------------------------------------------- 3236: @node double-ambcond, , The optional Double Number word set, The optional Double Number word set 3237: @subsection Ambiguous conditions 3238: @c --------------------------------------------------------------------- 3239: 3240: @table @i 3241: 3242: @item @var{d} outside of range of @var{n} in @code{D>S}: 3243: The least significant cell of @var{d} is produced. 3244: 3245: @end table 3246: 3247: 3248: @c ===================================================================== 3249: @node The optional Exception word set, The optional Facility word set, The optional Double Number word set, ANS conformance 3250: @section The optional Exception word set 3251: @c ===================================================================== 3252: 3253: @menu 3254: * exception-idef:: Implementation Defined Options 3255: @end menu 3256: 3257: 3258: @c --------------------------------------------------------------------- 3259: @node exception-idef, , The optional Exception word set, The optional Exception word set 3260: @subsection Implementation Defined Options 3261: @c --------------------------------------------------------------------- 3262: 3263: @table @i 3264: @item @code{THROW}-codes used in the system: 3265: The codes -256@minus{}-511 are used for reporting signals (see 3266: @file{errore.fs}). The codes -512@minus{}-2047 are used for OS errors 3267: (for file and memory allocation operations). The mapping from OS error 3268: numbers to throw code is -512@minus{}@code{errno}. One side effect of 3269: this mapping is that undefined OS errors produce a message with a 3270: strange number; e.g., @code{-1000 THROW} results in @code{Unknown error 3271: 488} on my system. 3272: @end table 3273: 3274: @c ===================================================================== 3275: @node The optional Facility word set, The optional File-Access word set, The optional Exception word set, ANS conformance 3276: @section The optional Facility word set 3277: @c ===================================================================== 3278: 3279: @menu 3280: * facility-idef:: Implementation Defined Options 3281: * facility-ambcond:: Ambiguous Conditions 3282: @end menu 3283: 3284: 3285: @c --------------------------------------------------------------------- 3286: @node facility-idef, facility-ambcond, The optional Facility word set, The optional Facility word set 3287: @subsection Implementation Defined Options 3288: @c --------------------------------------------------------------------- 3289: 3290: @table @i 3291: 3292: @item encoding of keyboard events (@code{EKEY}): 3293: Not yet implemeted. 3294: 3295: @item duration of a system clock tick 3296: System dependent. With respect to @code{MS}, the time is specified in 3297: microseconds. How well the OS and the hardware implement this, is 3298: another question. 3299: 3300: @item repeatability to be expected from the execution of @code{MS}: 3301: System dependent. On Unix, a lot depends on load. If the system is 3302: lightly loaded, and the delay is short enough that Gforth does not get 3303: swapped out, the performance should be acceptable. Under MS-DOS and 3304: other single-tasking systems, it should be good. 3305: 3306: @end table 3307: 3308: 3309: @c --------------------------------------------------------------------- 3310: @node facility-ambcond, , facility-idef, The optional Facility word set 3311: @subsection Ambiguous conditions 3312: @c --------------------------------------------------------------------- 3313: 3314: @table @i 3315: 3316: @item @code{AT-XY} can't be performed on user output device: 3317: Largely terminal dependant. No range checks are done on the arguments. 3318: No errors are reported. You may see some garbage appearing, you may see 3319: simply nothing happen. 3320: 3321: @end table 3322: 3323: 3324: @c ===================================================================== 3325: @node The optional File-Access word set, The optional Floating-Point word set, The optional Facility word set, ANS conformance 3326: @section The optional File-Access word set 3327: @c ===================================================================== 3328: 3329: @menu 3330: * file-idef:: Implementation Defined Options 3331: * file-ambcond:: Ambiguous Conditions 3332: @end menu 3333: 3334: 3335: @c --------------------------------------------------------------------- 3336: @node file-idef, file-ambcond, The optional File-Access word set, The optional File-Access word set 3337: @subsection Implementation Defined Options 3338: @c --------------------------------------------------------------------- 3339: 3340: @table @i 3341: 3342: @item File access methods used: 3343: @code{R/O}, @code{R/W} and @code{BIN} work as you would 3344: expect. @code{W/O} translates into the C file opening mode @code{w} (or 3345: @code{wb}): The file is cleared, if it exists, and created, if it does 3346: not (both with @code{open-file} and @code{create-file}). Under Unix 3347: @code{create-file} creates a file with 666 permissions modified by your 3348: umask. 3349: 3350: @item file exceptions: 3351: The file words do not raise exceptions (except, perhaps, memory access 3352: faults when you pass illegal addresses or file-ids). 3353: 3354: @item file line terminator: 3355: System-dependent. Gforth uses C's newline character as line 3356: terminator. What the actual character code(s) of this are is 3357: system-dependent. 3358: 3359: @item file name format 3360: System dependent. Gforth just uses the file name format of your OS. 3361: 3362: @item information returned by @code{FILE-STATUS}: 3363: @code{FILE-STATUS} returns the most powerful file access mode allowed 3364: for the file: Either @code{R/O}, @code{W/O} or @code{R/W}. If the file 3365: cannot be accessed, @code{R/O BIN} is returned. @code{BIN} is applicable 3366: along with the retured mode. 3367: 3368: @item input file state after an exception when including source: 3369: All files that are left via the exception are closed. 3370: 3371: @item @var{ior} values and meaning: 3372: The @var{ior}s returned by the file and memory allocation words are 3373: intended as throw codes. They typically are in the range 3374: -512@minus{}-2047 of OS errors. The mapping from OS error numbers to 3375: @var{ior}s is -512@minus{}@var{errno}. 3376: 3377: @item maximum depth of file input nesting: 3378: limited by the amount of return stack, locals/TIB stack, and the number 3379: of open files available. This should not give you troubles. 3380: 3381: @item maximum size of input line: 3382: @code{/line}. Currently 255. 3383: 3384: @item methods of mapping block ranges to files: 3385: By default, blocks are accessed in the file @file{blocks.fb} in the 3386: current working directory. The file can be switched with @code{USE}. 3387: 3388: @item number of string buffers provided by @code{S"}: 3389: 1 3390: 3391: @item size of string buffer used by @code{S"}: 3392: @code{/line}. currently 255. 3393: 3394: @end table 3395: 3396: @c --------------------------------------------------------------------- 3397: @node file-ambcond, , file-idef, The optional File-Access word set 3398: @subsection Ambiguous conditions 3399: @c --------------------------------------------------------------------- 3400: 3401: @table @i 3402: 3403: @item attempting to position a file outside it's boundaries: 3404: @code{REPOSITION-FILE} is performed as usual: Afterwards, 3405: @code{FILE-POSITION} returns the value given to @code{REPOSITION-FILE}. 3406: 3407: @item attempting to read from file positions not yet written: 3408: End-of-file, i.e., zero characters are read and no error is reported. 3409: 3410: @item @var{file-id} is invalid (@code{INCLUDE-FILE}): 3411: An appropriate exception may be thrown, but a memory fault or other 3412: problem is more probable. 3413: 3414: @item I/O exception reading or closing @var{file-id} (@code{include-file}, @code{included}): 3415: The @var{ior} produced by the operation, that discovered the problem, is 3416: thrown. 3417: 3418: @item named file cannot be opened (@code{included}): 3419: The @var{ior} produced by @code{open-file} is thrown. 3420: 3421: @item requesting an unmapped block number: 3422: There are no unmapped legal block numbers. On some operating systems, 3423: writing a block with a large number may overflow the file system and 3424: have an error message as consequence. 3425: 3426: @item using @code{source-id} when @code{blk} is non-zero: 3427: @code{source-id} performs its function. Typically it will give the id of 3428: the source which loaded the block. (Better ideas?) 3429: 3430: @end table 3431: 3432: 3433: @c ===================================================================== 3434: @node The optional Floating-Point word set, The optional Locals word set, The optional File-Access word set, ANS conformance 3435: @section The optional Floating-Point word set 3436: @c ===================================================================== 3437: 3438: @menu 3439: * floating-idef:: Implementation Defined Options 3440: * floating-ambcond:: Ambiguous Conditions 3441: @end menu 3442: 3443: 3444: @c --------------------------------------------------------------------- 3445: @node floating-idef, floating-ambcond, The optional Floating-Point word set, The optional Floating-Point word set 3446: @subsection Implementation Defined Options 3447: @c --------------------------------------------------------------------- 3448: 3449: @table @i 3450: 3451: @item format and range of floating point numbers: 3452: System-dependent; the @code{double} type of C. 3453: 3454: @item results of @code{REPRESENT} when @var{float} is out of range: 3455: System dependent; @code{REPRESENT} is implemented using the C library 3456: function @code{ecvt()} and inherits its behaviour in this respect. 3457: 3458: @item rounding or truncation of floating-point numbers: 3459: System dependent; the rounding behaviour is inherited from the hosting C 3460: compiler. IEEE-FP-based (i.e., most) systems by default round to 3461: nearest, and break ties by rounding to even (i.e., such that the last 3462: bit of the mantissa is 0). 3463: 3464: @item size of floating-point stack: 3465: @code{s" FLOATING-STACK" environment? drop .}. Can be changed at startup 3466: with the command-line option @code{-f}. 3467: 3468: @item width of floating-point stack: 3469: @code{1 floats}. 3470: 3471: @end table 3472: 3473: 3474: @c --------------------------------------------------------------------- 3475: @node floating-ambcond, , floating-idef, The optional Floating-Point word set 3476: @subsection Ambiguous conditions 3477: @c --------------------------------------------------------------------- 3478: 3479: @table @i 3480: 3481: @item @code{df@@} or @code{df!} used with an address that is not double-float aligned: 3482: System-dependent. Typically results in a @code{-23 THROW} like other 3483: alignment violations. 3484: 3485: @item @code{f@@} or @code{f!} used with an address that is not float aligned: 3486: System-dependent. Typically results in a @code{-23 THROW} like other 3487: alignment violations. 3488: 3489: @item Floating-point result out of range: 3490: System-dependent. Can result in a @code{-55 THROW} (Floating-point 3491: unidentified fault), or can produce a special value representing, e.g., 3492: Infinity. 3493: 3494: @item @code{sf@@} or @code{sf!} used with an address that is not single-float aligned: 3495: System-dependent. Typically results in an alignment fault like other 3496: alignment violations. 3497: 3498: @item BASE is not decimal (@code{REPRESENT}, @code{F.}, @code{FE.}, @code{FS.}): 3499: The floating-point number is converted into decimal nonetheless. 3500: 3501: @item Both arguments are equal to zero (@code{FATAN2}): 3502: System-dependent. @code{FATAN2} is implemented using the C library 3503: function @code{atan2()}. 3504: 3505: @item Using ftan on an argument @var{r1} where cos(@var{r1}) is zero: 3506: System-dependent. Anyway, typically the cos of @var{r1} will not be zero 3507: because of small errors and the tan will be a very large (or very small) 3508: but finite number. 3509: 3510: @item @var{d} cannot be presented precisely as a float in @code{D>F}: 3511: The result is rounded to the nearest float. 3512: 3513: @item dividing by zero: 3514: @code{-55 throw} (Floating-point unidentified fault) 3515: 3516: @item exponent too big for conversion (@code{DF!}, @code{DF@@}, @code{SF!}, @code{SF@@}): 3517: System dependent. On IEEE-FP based systems the number is converted into 3518: an infinity. 3519: 3520: @item @var{float}<1 (@code{facosh}): 3521: @code{-55 throw} (Floating-point unidentified fault) 3522: 3523: @item @var{float}=<-1 (@code{flnp1}): 3524: @code{-55 throw} (Floating-point unidentified fault). On IEEE-FP systems 3525: negative infinity is typically produced for @var{float}=-1. 3526: 3527: @item @var{float}=<0 (@code{fln}, @code{flog}): 3528: @code{-55 throw} (Floating-point unidentified fault). On IEEE-FP systems 3529: negative infinity is typically produced for @var{float}=0. 3530: 3531: @item @var{float}<0 (@code{fasinh}, @code{fsqrt}): 3532: @code{-55 throw} (Floating-point unidentified fault). @code{fasinh} 3533: produces values for these inputs on my Linux box (Bug in the C library?) 3534: 3535: @item |@var{float}|>1 (@code{facos}, @code{fasin}, @code{fatanh}): 3536: @code{-55 throw} (Floating-point unidentified fault). 3537: 3538: @item integer part of float cannot be represented by @var{d} in @code{f>d}: 3539: @code{-55 throw} (Floating-point unidentified fault). 3540: 3541: @item string larger than pictured numeric output area (@code{f.}, @code{fe.}, @code{fs.}): 3542: This does not happen. 3543: @end table 3544: 3545: 3546: 3547: @c ===================================================================== 3548: @node The optional Locals word set, The optional Memory-Allocation word set, The optional Floating-Point word set, ANS conformance 3549: @section The optional Locals word set 3550: @c ===================================================================== 3551: 3552: @menu 3553: * locals-idef:: Implementation Defined Options 3554: * locals-ambcond:: Ambiguous Conditions 3555: @end menu 3556: 3557: 3558: @c --------------------------------------------------------------------- 3559: @node locals-idef, locals-ambcond, The optional Locals word set, The optional Locals word set 3560: @subsection Implementation Defined Options 3561: @c --------------------------------------------------------------------- 3562: 3563: @table @i 3564: 3565: @item maximum number of locals in a definition: 3566: @code{s" #locals" environment? drop .}. Currently 15. This is a lower 3567: bound, e.g., on a 32-bit machine there can be 41 locals of up to 8 3568: characters. The number of locals in a definition is bounded by the size 3569: of locals-buffer, which contains the names of the locals. 3570: 3571: @end table 3572: 3573: 3574: @c --------------------------------------------------------------------- 3575: @node locals-ambcond, , locals-idef, The optional Locals word set 3576: @subsection Ambiguous conditions 3577: @c --------------------------------------------------------------------- 3578: 3579: @table @i 3580: 3581: @item executing a named local in interpretation state: 3582: @code{-14 throw} (Interpreting a compile-only word). 3583: 3584: @item @var{name} not defined by @code{VALUE} or @code{(LOCAL)} (@code{TO}): 3585: @code{-32 throw} (Invalid name argument) 3586: 3587: @end table 3588: 3589: 3590: @c ===================================================================== 3591: @node The optional Memory-Allocation word set, The optional Programming-Tools word set, The optional Locals word set, ANS conformance 3592: @section The optional Memory-Allocation word set 3593: @c ===================================================================== 3594: 3595: @menu 3596: * memory-idef:: Implementation Defined Options 3597: @end menu 3598: 3599: 3600: @c --------------------------------------------------------------------- 3601: @node memory-idef, , The optional Memory-Allocation word set, The optional Memory-Allocation word set 3602: @subsection Implementation Defined Options 3603: @c --------------------------------------------------------------------- 3604: 3605: @table @i 3606: 3607: @item values and meaning of @var{ior}: 3608: The @var{ior}s returned by the file and memory allocation words are 3609: intended as throw codes. They typically are in the range 3610: -512@minus{}-2047 of OS errors. The mapping from OS error numbers to 3611: @var{ior}s is -512@minus{}@var{errno}. 3612: 3613: @end table 3614: 3615: @c ===================================================================== 3616: @node The optional Programming-Tools word set, The optional Search-Order word set, The optional Memory-Allocation word set, ANS conformance 3617: @section The optional Programming-Tools word set 3618: @c ===================================================================== 3619: 3620: @menu 3621: * programming-idef:: Implementation Defined Options 3622: * programming-ambcond:: Ambiguous Conditions 3623: @end menu 3624: 3625: 3626: @c --------------------------------------------------------------------- 3627: @node programming-idef, programming-ambcond, The optional Programming-Tools word set, The optional Programming-Tools word set 3628: @subsection Implementation Defined Options 3629: @c --------------------------------------------------------------------- 3630: 3631: @table @i 3632: 3633: @item ending sequence for input following @code{;code} and @code{code}: 3634: @code{end-code} 3635: 3636: @item manner of processing input following @code{;code} and @code{code}: 3637: The @code{assembler} vocabulary is pushed on the search order stack, and 3638: the input is processed by the text interpreter, (starting) in interpret 3639: state. 3640: 3641: @item search order capability for @code{EDITOR} and @code{ASSEMBLER}: 3642: The ANS Forth search order word set. 3643: 3644: @item source and format of display by @code{SEE}: 3645: The source for @code{see} is the intermediate code used by the inner 3646: interpreter. The current @code{see} tries to output Forth source code 3647: as well as possible. 3648: 3649: @end table 3650: 3651: @c --------------------------------------------------------------------- 3652: @node programming-ambcond, , programming-idef, The optional Programming-Tools word set 3653: @subsection Ambiguous conditions 3654: @c --------------------------------------------------------------------- 3655: 3656: @table @i 3657: 3658: @item deleting the compilation wordlist (@code{FORGET}): 3659: Not implemented (yet). 3660: 3661: @item fewer than @var{u}+1 items on the control flow stack (@code{CS-PICK}, @code{CS-ROLL}): 3662: This typically results in an @code{abort"} with a descriptive error 3663: message (may change into a @code{-22 throw} (Control structure mismatch) 3664: in the future). You may also get a memory access error. If you are 3665: unlucky, this ambiguous condition is not caught. 3666: 3667: @item @var{name} can't be found (@code{forget}): 3668: Not implemented (yet). 3669: 3670: @item @var{name} not defined via @code{CREATE}: 3671: @code{;code} behaves like @code{DOES>} in this respect, i.e., it changes 3672: the execution semantics of the last defined word no matter how it was 3673: defined. 3674: 3675: @item @code{POSTPONE} applied to @code{[IF]}: 3676: After defining @code{: X POSTPONE [IF] ; IMMEDIATE}. @code{X} is 3677: equivalent to @code{[IF]}. 3678: 3679: @item reaching the end of the input source before matching @code{[ELSE]} or @code{[THEN]}: 3680: Continue in the same state of conditional compilation in the next outer 3681: input source. Currently there is no warning to the user about this. 3682: 3683: @item removing a needed definition (@code{FORGET}): 3684: Not implemented (yet). 3685: 3686: @end table 3687: 3688: 3689: @c ===================================================================== 3690: @node The optional Search-Order word set, , The optional Programming-Tools word set, ANS conformance 3691: @section The optional Search-Order word set 3692: @c ===================================================================== 3693: 3694: @menu 3695: * search-idef:: Implementation Defined Options 3696: * search-ambcond:: Ambiguous Conditions 3697: @end menu 3698: 3699: 3700: @c --------------------------------------------------------------------- 3701: @node search-idef, search-ambcond, The optional Search-Order word set, The optional Search-Order word set 3702: @subsection Implementation Defined Options 3703: @c --------------------------------------------------------------------- 3704: 3705: @table @i 3706: 3707: @item maximum number of word lists in search order: 3708: @code{s" wordlists" environment? drop .}. Currently 16. 3709: 3710: @item minimum search order: 3711: @code{root root}. 3712: 3713: @end table 3714: 3715: @c --------------------------------------------------------------------- 3716: @node search-ambcond, , search-idef, The optional Search-Order word set 3717: @subsection Ambiguous conditions 3718: @c --------------------------------------------------------------------- 3719: 3720: @table @i 3721: 3722: @item changing the compilation wordlist (during compilation): 3723: The word is entered into the wordlist that was the compilation wordlist 3724: at the start of the definition. Any changes to the name field (e.g., 3725: @code{immediate}) or the code field (e.g., when executing @code{DOES>}) 3726: are applied to the latest defined word (as reported by @code{last} or 3727: @code{lastxt}), if possible, irrespective of the compilation wordlist. 3728: 3729: @item search order empty (@code{previous}): 3730: @code{abort" Vocstack empty"}. 3731: 3732: @item too many word lists in search order (@code{also}): 3733: @code{abort" Vocstack full"}. 3734: 3735: @end table 3736: 3737: @node Model, Integrating Gforth, ANS conformance, Top 3738: @chapter Model 3739: 3740: This chapter has yet to be written. It will contain information, on 3741: which internal structures you can rely. 3742: 3743: @node Integrating Gforth, Emacs and Gforth, Model, Top 3744: @chapter Integrating Gforth into C programs 3745: 3746: This is not yet implemented. 3747: 3748: Several people like to use Forth as scripting language for applications 3749: that are otherwise written in C, C++, or some other language. 3750: 3751: The Forth system ATLAST provides facilities for embedding it into 3752: applications; unfortunately it has several disadvantages: most 3753: importantly, it is not based on ANS Forth, and it is apparently dead 3754: (i.e., not developed further and not supported). The facilities 3755: provided by Gforth in this area are inspired by ATLASTs facilities, so 3756: making the switch should not be hard. 3757: 3758: We also tried to design the interface such that it can easily be 3759: implemented by other Forth systems, so that we may one day arrive at a 3760: standardized interface. Such a standard interface would allow you to 3761: replace the Forth system without having to rewrite C code. 3762: 3763: You embed the Gforth interpreter by linking with the library 3764: @code{libgforth.a} (give the compiler the option @code{-lgforth}). All 3765: global symbols in this library that belong to the interface, have the 3766: prefix @code{forth_}. (Global symbols that are used internally have the 3767: prefix @code{gforth_}). 3768: 3769: You can include the declarations of Forth types and the functions and 3770: variables of the interface with @code{#include <forth.h>}. 3771: 3772: Types. 3773: 3774: Variables. 3775: 3776: Data and FP Stack pointer. Area sizes. 3777: 3778: functions. 3779: 3780: forth_init(imagefile) 3781: forth_evaluate(string) exceptions? 3782: forth_goto(address) (or forth_execute(xt)?) 3783: forth_continue() (a corountining mechanism) 3784: 3785: Adding primitives. 3786: 3787: No checking. 3788: 3789: Signals? 3790: 3791: Accessing the Stacks 3792: 3793: @node Emacs and Gforth, Internals, Integrating Gforth, Top 3794: @chapter Emacs and Gforth 3795: 3796: Gforth comes with @file{gforth.el}, an improved version of 3797: @file{forth.el} by Goran Rydqvist (included in the TILE package). The 3798: improvements are a better (but still not perfect) handling of 3799: indentation. I have also added comment paragraph filling (@kbd{M-q}), 3800: commenting (@kbd{C-x \}) and uncommenting (@kbd{C-u C-x \}) regions and 3801: removing debugging tracers (@kbd{C-x ~}, @pxref{Debugging}). I left the 3802: stuff I do not use alone, even though some of it only makes sense for 3803: TILE. To get a description of these features, enter Forth mode and type 3804: @kbd{C-h m}. 3805: 3806: In addition, Gforth supports Emacs quite well: The source code locations 3807: given in error messages, debugging output (from @code{~~}) and failed 3808: assertion messages are in the right format for Emacs' compilation mode 3809: (@pxref{Compilation, , Running Compilations under Emacs, emacs, Emacs 3810: Manual}) so the source location corresponding to an error or other 3811: message is only a few keystrokes away (@kbd{C-x `} for the next error, 3812: @kbd{C-c C-c} for the error under the cursor). 3813: 3814: Also, if you @code{include} @file{etags.fs}, a new @file{TAGS} file 3815: (@pxref{Tags, , Tags Tables, emacs, Emacs Manual}) will be produced that 3816: contains the definitions of all words defined afterwards. You can then 3817: find the source for a word using @kbd{M-.}. Note that emacs can use 3818: several tags files at the same time (e.g., one for the Gforth sources 3819: and one for your program, @pxref{Select Tags Table,,Selecting a Tags 3820: Table,emacs, Emacs Manual}). The TAGS file for the preloaded words is 3821: @file{$(datadir)/gforth/$(VERSION)/TAGS} (e.g., 3822: @file{/usr/local/share/gforth/0.2.0/TAGS}). 3823: 3824: To get all these benefits, add the following lines to your @file{.emacs} 3825: file: 3826: 3827: @example 3828: (autoload 'forth-mode "gforth.el") 3829: (setq auto-mode-alist (cons '("\\.fs\\'" . forth-mode) auto-mode-alist)) 3830: @end example 3831: 3832: @node Internals, Bugs, Emacs and Gforth, Top 3833: @chapter Internals 3834: 3835: Reading this section is not necessary for programming with Gforth. It 3836: should be helpful for finding your way in the Gforth sources. 3837: 3838: The ideas in this section have also been published in the papers 3839: @cite{ANS fig/GNU/??? Forth} (in German) by Bernd Paysan, presented at 3840: the Forth-Tagung '93 and @cite{A Portable Forth Engine} by M. Anton 3841: Ertl, presented at EuroForth '93; the latter is available at 3842: @*@file{}. 3843: 3844: @menu 3845: * Portability:: 3846: * Threading:: 3847: * Primitives:: 3848: * System Architecture:: 3849: * Performance:: 3850: @end menu 3851: 3852: @node Portability, Threading, Internals, Internals 3853: @section Portability 3854: 3855: One of the main goals of the effort is availability across a wide range 3856: of personal machines. fig-Forth, and, to a lesser extent, F83, achieved 3857: this goal by manually coding the engine in assembly language for several 3858: then-popular processors. This approach is very labor-intensive and the 3859: results are short-lived due to progress in computer architecture. 3860: 3861: Others have avoided this problem by coding in C, e.g., Mitch Bradley 3862: (cforth), Mikael Patel (TILE) and Dirk Zoller (pfe). This approach is 3863: particularly popular for UNIX-based Forths due to the large variety of 3864: architectures of UNIX machines. Unfortunately an implementation in C 3865: does not mix well with the goals of efficiency and with using 3866: traditional techniques: Indirect or direct threading cannot be expressed 3867: in C, and switch threading, the fastest technique available in C, is 3868: significantly slower. Another problem with C is that it's very 3869: cumbersome to express double integer arithmetic. 3870: 3871: Fortunately, there is a portable language that does not have these 3872: limitations: GNU C, the version of C processed by the GNU C compiler 3873: (@pxref{C Extensions, , Extensions to the C Language Family, gcc.info, 3874: GNU C Manual}). Its labels as values feature (@pxref{Labels as Values, , 3875: Labels as Values, gcc.info, GNU C Manual}) makes direct and indirect 3876: threading possible, its @code{long long} type (@pxref{Long Long, , 3877: Double-Word Integers, gcc.info, GNU C Manual}) corresponds to Forth's 3878: double numbers@footnote{Unfortunately, long longs are not implemented 3879: properly on all machines (e.g., on alpha-osf1, long longs are only 64 3880: bits, the same size as longs (and pointers), but they should be twice as 3881: long according to @ref{Long Long, , Double-Word Integers, gcc.info, GNU 3882: C Manual}). So, we had to implement doubles in C after all. Still, on 3883: most machines we can use long longs and achieve better performance than 3884: with the emulation package.}. GNU C is available for free on all 3885: important (and many unimportant) UNIX machines, VMS, 80386s running 3886: MS-DOS, the Amiga, and the Atari ST, so a Forth written in GNU C can run 3887: on all these machines. 3888: 3889: Writing in a portable language has the reputation of producing code that 3890: is slower than assembly. For our Forth engine we repeatedly looked at 3891: the code produced by the compiler and eliminated most compiler-induced 3892: inefficiencies by appropriate changes in the source-code. 3893: 3894: However, register allocation cannot be portably influenced by the 3895: programmer, leading to some inefficiencies on register-starved 3896: machines. We use explicit register declarations (@pxref{Explicit Reg 3897: Vars, , Variables in Specified Registers, gcc.info, GNU C Manual}) to 3898: improve the speed on some machines. They are turned on by using the 3899: @code{gcc} switch @code{-DFORCE_REG}. Unfortunately, this feature not 3900: only depends on the machine, but also on the compiler version: On some 3901: machines some compiler versions produce incorrect code when certain 3902: explicit register declarations are used. So by default 3903: @code{-DFORCE_REG} is not used. 3904: 3905: @node Threading, Primitives, Portability, Internals 3906: @section Threading 3907: 3908: GNU C's labels as values extension (available since @code{gcc-2.0}, 3909: @pxref{Labels as Values, , Labels as Values, gcc.info, GNU C Manual}) 3910: makes it possible to take the address of @var{label} by writing 3911: @code{&&@var{label}}. This address can then be used in a statement like 3912: @code{goto *@var{address}}. I.e., @code{goto *&&x} is the same as 3913: @code{goto x}. 3914: 3915: With this feature an indirect threaded NEXT looks like: 3916: @example 3917: cfa = *ip++; 3918: ca = *cfa; 3919: goto *ca; 3920: @end example 3921: For those unfamiliar with the names: @code{ip} is the Forth instruction 3922: pointer; the @code{cfa} (code-field address) corresponds to ANS Forths 3923: execution token and points to the code field of the next word to be 3924: executed; The @code{ca} (code address) fetched from there points to some 3925: executable code, e.g., a primitive or the colon definition handler 3926: @code{docol}. 3927: 3928: Direct threading is even simpler: 3929: @example 3930: ca = *ip++; 3931: goto *ca; 3932: @end example 3933: 3934: Of course we have packaged the whole thing neatly in macros called 3935: @code{NEXT} and @code{NEXT1} (the part of NEXT after fetching the cfa). 3936: 3937: @menu 3938: * Scheduling:: 3939: * Direct or Indirect Threaded?:: 3940: * DOES>:: 3941: @end menu 3942: 3943: @node Scheduling, Direct or Indirect Threaded?, Threading, Threading 3944: @subsection Scheduling 3945: 3946: There is a little complication: Pipelined and superscalar processors, 3947: i.e., RISC and some modern CISC machines can process independent 3948: instructions while waiting for the results of an instruction. The 3949: compiler usually reorders (schedules) the instructions in a way that 3950: achieves good usage of these delay slots. However, on our first tries 3951: the compiler did not do well on scheduling primitives. E.g., for 3952: @code{+} implemented as 3953: @example 3954: n=sp[0]+sp[1]; 3955: sp++; 3956: sp[0]=n; 3957: NEXT; 3958: @end example 3959: the NEXT comes strictly after the other code, i.e., there is nearly no 3960: scheduling. After a little thought the problem becomes clear: The 3961: compiler cannot know that sp and ip point to different addresses (and 3962: the version of @code{gcc} we used would not know it even if it was 3963: possible), so it could not move the load of the cfa above the store to 3964: the TOS. Indeed the pointers could be the same, if code on or very near 3965: the top of stack were executed. In the interest of speed we chose to 3966: forbid this probably unused ``feature'' and helped the compiler in 3967: scheduling: NEXT is divided into the loading part (@code{NEXT_P1}) and 3968: the goto part (@code{NEXT_P2}). @code{+} now looks like: 3969: @example 3970: n=sp[0]+sp[1]; 3971: sp++; 3972: NEXT_P1; 3973: sp[0]=n; 3974: NEXT_P2; 3975: @end example 3976: This can be scheduled optimally by the compiler. 3977: 3978: This division can be turned off with the switch @code{-DCISC_NEXT}. This 3979: switch is on by default on machines that do not profit from scheduling 3980: (e.g., the 80386), in order to preserve registers. 3981: 3982: @node Direct or Indirect Threaded?, DOES>, Scheduling, Threading 3983: @subsection Direct or Indirect Threaded? 3984: 3985: Both! After packaging the nasty details in macro definitions we 3986: realized that we could switch between direct and indirect threading by 3987: simply setting a compilation flag (@code{-DDIRECT_THREADED}) and 3988: defining a few machine-specific macros for the direct-threading case. 3989: On the Forth level we also offer access words that hide the 3990: differences between the threading methods (@pxref{Threading Words}). 3991: 3992: Indirect threading is implemented completely 3993: machine-independently. Direct threading needs routines for creating 3994: jumps to the executable code (e.g. to docol or dodoes). These routines 3995: are inherently machine-dependent, but they do not amount to many source 3996: lines. I.e., even porting direct threading to a new machine is a small 3997: effort. 3998: 3999: @node DOES>, , Direct or Indirect Threaded?, Threading 4000: @subsection DOES> 4001: One of the most complex parts of a Forth engine is @code{dodoes}, i.e., 4002: the chunk of code executed by every word defined by a 4003: @code{CREATE}...@code{DOES>} pair. The main problem here is: How to find 4004: the Forth code to be executed, i.e. the code after the @code{DOES>} (the 4005: DOES-code)? There are two solutions: 4006: 4007: In fig-Forth the code field points directly to the dodoes and the 4008: DOES-code address is stored in the cell after the code address 4009: (i.e. at cfa cell+). It may seem that this solution is illegal in the 4010: Forth-79 and all later standards, because in fig-Forth this address 4011: lies in the body (which is illegal in these standards). However, by 4012: making the code field larger for all words this solution becomes legal 4013: again. We use this approach for the indirect threaded version. Leaving 4014: a cell unused in most words is a bit wasteful, but on the machines we 4015: are targetting this is hardly a problem. The other reason for having a 4016: code field size of two cells is to avoid having different image files 4017: for direct and indirect threaded systems (@pxref{System Architecture}). 4018: 4019: The other approach is that the code field points or jumps to the cell 4020: after @code{DOES}. In this variant there is a jump to @code{dodoes} at 4021: this address. @code{dodoes} can then get the DOES-code address by 4022: computing the code address, i.e., the address of the jump to dodoes, 4023: and add the length of that jump field. A variant of this is to have a 4024: call to @code{dodoes} after the @code{DOES>}; then the return address 4025: (which can be found in the return register on RISCs) is the DOES-code 4026: address. Since the two cells available in the code field are usually 4027: used up by the jump to the code address in direct threading, we use 4028: this approach for direct threading. We did not want to add another 4029: cell to the code field. 4030: 4031: @node Primitives, System Architecture, Threading, Internals 4032: @section Primitives 4033: 4034: @menu 4035: * Automatic Generation:: 4036: * TOS Optimization:: 4037: * Produced code:: 4038: @end menu 4039: 4040: @node Automatic Generation, TOS Optimization, Primitives, Primitives 4041: @subsection Automatic Generation 4042: 4043: Since the primitives are implemented in a portable language, there is no 4044: longer any need to minimize the number of primitives. On the contrary, 4045: having many primitives is an advantage: speed. In order to reduce the 4046: number of errors in primitives and to make programming them easier, we 4047: provide a tool, the primitive generator (@file{prims2x.fs}), that 4048: automatically generates most (and sometimes all) of the C code for a 4049: primitive from the stack effect notation. The source for a primitive 4050: has the following form: 4051: 4052: @format 4053: @var{Forth-name} @var{stack-effect} @var{category} [@var{pronounc.}] 4054: [@code{""}@var{glossary entry}@code{""}] 4055: @var{C code} 4056: [@code{:} 4057: @var{Forth code}] 4058: @end format 4059: 4060: The items in brackets are optional. The category and glossary fields 4061: are there for generating the documentation, the Forth code is there 4062: for manual implementations on machines without GNU C. E.g., the source 4063: for the primitive @code{+} is: 4064: @example 4065: + n1 n2 -- n core plus 4066: n = n1+n2; 4067: @end example 4068: 4069: This looks like a specification, but in fact @code{n = n1+n2} is C 4070: code. Our primitive generation tool extracts a lot of information from 4071: the stack effect notations@footnote{We use a one-stack notation, even 4072: though we have separate data and floating-point stacks; The separate 4073: notation can be generated easily from the unified notation.}: The number 4074: of items popped from and pushed on the stack, their type, and by what 4075: name they are referred to in the C code. It then generates a C code 4076: prelude and postlude for each primitive. The final C code for @code{+} 4077: looks like this: 4078: 4079: @example 4080: I_plus: /* + ( n1 n2 -- n ) */ /* label, stack effect */ 4081: /* */ /* documentation */ 4082: @{ 4083: DEF_CA /* definition of variable ca (indirect threading) */ 4084: Cell n1; /* definitions of variables */ 4085: Cell n2; 4086: Cell n; 4087: n1 = (Cell) sp[1]; /* input */ 4088: n2 = (Cell) TOS; 4089: sp += 1; /* stack adjustment */ 4090: NAME("+") /* debugging output (with -DDEBUG) */ 4091: @{ 4092: n = n1+n2; /* C code taken from the source */ 4093: @} 4094: NEXT_P1; /* NEXT part 1 */ 4095: TOS = (Cell)n; /* output */ 4096: NEXT_P2; /* NEXT part 2 */ 4097: @} 4098: @end example 4099: 4100: This looks long and inefficient, but the GNU C compiler optimizes quite 4101: well and produces optimal code for @code{+} on, e.g., the R3000 and the 4102: HP RISC machines: Defining the @code{n}s does not produce any code, and 4103: using them as intermediate storage also adds no cost. 4104: 4105: There are also other optimizations, that are not illustrated by this 4106: example: Assignments between simple variables are usually for free (copy 4107: propagation). If one of the stack items is not used by the primitive 4108: (e.g. in @code{drop}), the compiler eliminates the load from the stack 4109: (dead code elimination). On the other hand, there are some things that 4110: the compiler does not do, therefore they are performed by 4111: @file{prims2x.fs}: The compiler does not optimize code away that stores 4112: a stack item to the place where it just came from (e.g., @code{over}). 4113: 4114: While programming a primitive is usually easy, there are a few cases 4115: where the programmer has to take the actions of the generator into 4116: account, most notably @code{?dup}, but also words that do not (always) 4117: fall through to NEXT. 4118: 4119: @node TOS Optimization, Produced code, Automatic Generation, Primitives 4120: @subsection TOS Optimization 4121: 4122: An important optimization for stack machine emulators, e.g., Forth 4123: engines, is keeping one or more of the top stack items in 4124: registers. If a word has the stack effect @var{in1}...@var{inx} @code{--} 4125: @var{out1}...@var{outy}, keeping the top @var{n} items in registers 4126: @itemize @bullet 4127: @item 4128: is better than keeping @var{n-1} items, if @var{x>=n} and @var{y>=n}, 4129: due to fewer loads from and stores to the stack. 4130: @item is slower than keeping @var{n-1} items, if @var{x<>y} and @var{x<n} and 4131: @var{y<n}, due to additional moves between registers. 4132: @end itemize 4133: 4134: In particular, keeping one item in a register is never a disadvantage, 4135: if there are enough registers. Keeping two items in registers is a 4136: disadvantage for frequent words like @code{?branch}, constants, 4137: variables, literals and @code{i}. Therefore our generator only produces 4138: code that keeps zero or one items in registers. The generated C code 4139: covers both cases; the selection between these alternatives is made at 4140: C-compile time using the switch @code{-DUSE_TOS}. @code{TOS} in the C 4141: code for @code{+} is just a simple variable name in the one-item case, 4142: otherwise it is a macro that expands into @code{sp[0]}. Note that the 4143: GNU C compiler tries to keep simple variables like @code{TOS} in 4144: registers, and it usually succeeds, if there are enough registers. 4145: 4146: The primitive generator performs the TOS optimization for the 4147: floating-point stack, too (@code{-DUSE_FTOS}). For floating-point 4148: operations the benefit of this optimization is even larger: 4149: floating-point operations take quite long on most processors, but can be 4150: performed in parallel with other operations as long as their results are 4151: not used. If the FP-TOS is kept in a register, this works. If 4152: it is kept on the stack, i.e., in memory, the store into memory has to 4153: wait for the result of the floating-point operation, lengthening the 4154: execution time of the primitive considerably. 4155: 4156: The TOS optimization makes the automatic generation of primitives a 4157: bit more complicated. Just replacing all occurrences of @code{sp[0]} by 4158: @code{TOS} is not sufficient. There are some special cases to 4159: consider: 4160: @itemize @bullet 4161: @item In the case of @code{dup ( w -- w w )} the generator must not 4162: eliminate the store to the original location of the item on the stack, 4163: if the TOS optimization is turned on. 4164: @item Primitives with stack effects of the form @code{--} 4165: @var{out1}...@var{outy} must store the TOS to the stack at the start. 4166: Likewise, primitives with the stack effect @var{in1}...@var{inx} @code{--} 4167: must load the TOS from the stack at the end. But for the null stack 4168: effect @code{--} no stores or loads should be generated. 4169: @end itemize 4170: 4171: @node Produced code, , TOS Optimization, Primitives 4172: @subsection Produced code 4173: 4174: To see what assembly code is produced for the primitives on your machine 4175: with your compiler and your flag settings, type @code{make engine.s} and 4176: look at the resulting file @file{engine.s}. 4177: 4178: @node System Architecture, Performance, Primitives, Internals 4179: @section System Architecture 4180: 4181: Our Forth system consists not only of primitives, but also of 4182: definitions written in Forth. Since the Forth compiler itself belongs 4183: to those definitions, it is not possible to start the system with the 4184: primitives and the Forth source alone. Therefore we provide the Forth 4185: code as an image file in nearly executable form. At the start of the 4186: system a C routine loads the image file into memory, sets up the 4187: memory (stacks etc.) according to information in the image file, and 4188: starts executing Forth code. 4189: 4190: The image file format is a compromise between the goals of making it 4191: easy to generate image files and making them portable. The easiest way 4192: to generate an image file is to just generate a memory dump. However, 4193: this kind of image file cannot be used on a different machine, or on 4194: the next version of the engine on the same machine, it even might not 4195: work with the same engine compiled by a different version of the C 4196: compiler. We would like to have as few versions of the image file as 4197: possible, because we do not want to distribute many versions of the 4198: same image file, and to make it easy for the users to use their image 4199: files on many machines. We currently need to create a different image 4200: file for machines with different cell sizes and different byte order 4201: (little- or big-endian)@footnote{We are considering adding information to the 4202: image file that enables the loader to change the byte order.}. 4203: 4204: Forth code that is going to end up in a portable image file has to 4205: comply to some restrictions: addresses have to be stored in memory with 4206: special words (@code{A!}, @code{A,}, etc.) in order to make the code 4207: relocatable. Cells, floats, etc., have to be stored at the natural 4208: alignment boundaries@footnote{E.g., store floats (8 bytes) at an address 4209: dividable by~8. This happens automatically in our system when you use 4210: the ANS Forth alignment words.}, in order to avoid alignment faults on 4211: machines with stricter alignment. The image file is produced by a 4212: metacompiler (@file{cross.fs}). 4213: 4214: So, unlike the image file of Mitch Bradleys @code{cforth}, our image 4215: file is not directly executable, but has to undergo some manipulations 4216: during loading. Address relocation is performed at image load-time, not 4217: at run-time. The loader also has to replace tokens standing for 4218: primitive calls with the appropriate code-field addresses (or code 4219: addresses in the case of direct threading). 4220: 4221: @node Performance, , System Architecture, Internals 4222: @section Performance 4223: 4224: On RISCs the Gforth engine is very close to optimal; i.e., it is usually 4225: impossible to write a significantly faster engine. 4226: 4227: On register-starved machines like the 386 architecture processors 4228: improvements are possible, because @code{gcc} does not utilize the 4229: registers as well as a human, even with explicit register declarations; 4230: e.g., Bernd Beuster wrote a Forth system fragment in assembly language 4231: and hand-tuned it for the 486; this system is 1.19 times faster on the 4232: Sieve benchmark on a 486DX2/66 than Gforth compiled with 4233: @code{gcc-2.6.3} with @code{-DFORCE_REG}. 4234: 4235: However, this potential advantage of assembly language implementations 4236: is not necessarily realized in complete Forth systems: We compared 4237: Gforth (direct threaded, compiled with @code{gcc-2.6.3} and 4238: @code{-DFORCE_REG}) with Win32Forth 1.2093, LMI's NT Forth (Beta, May 4239: 1994) and Eforth (with and without peephole (aka pinhole) optimization 4240: of the threaded code); all these systems were written in assembly 4241: language. We also compared Gforth with three systems written in C: 4242: PFE-0.9.14 (compiled with @code{gcc-2.6.3} with the default 4243: configuration for Linux: @code{-O2 -fomit-frame-pointer -DUSE_REGS 4244: -DUNROLL_NEXT}), ThisForth Beta (compiled with gcc-2.6.3 -O3 4245: -fomit-frame-pointer; ThisForth employs peephole optimization of the 4246: threaded code) and TILE (compiled with @code{make opt}). We benchmarked 4247: Gforth, PFE, ThisForth and TILE on a 486DX2/66 under Linux. Kenneth 4248: O'Heskin kindly provided the results for Win32Forth and NT Forth on a 4249: 486DX2/66 with similar memory performance under Windows NT. Marcel 4250: Hendrix ported Eforth to Linux, then extended it to run the benchmarks, 4251: added the peephole optimizer, ran the benchmarks and reported the 4252: results. 4253: 4254: We used four small benchmarks: the ubiquitous Sieve; bubble-sorting and 4255: matrix multiplication come from the Stanford integer benchmarks and have 4256: been translated into Forth by Martin Fraeman; we used the versions 4257: included in the TILE Forth package, but with bigger data set sizes; and 4258: a recursive Fibonacci number computation for benchmarking calling 4259: performance. The following table shows the time taken for the benchmarks 4260: scaled by the time taken by Gforth (in other words, it shows the speedup 4261: factor that Gforth achieved over the other systems). 4262: 4263: @example 4264: relative Win32- NT eforth This- 4265: time Gforth Forth Forth eforth +opt PFE Forth TILE 4266: sieve 1.00 1.39 1.14 1.39 0.85 1.58 3.18 8.58 4267: bubble 1.00 1.31 1.41 1.48 0.88 1.50 3.88 4268: matmul 1.00 1.47 1.35 1.46 0.74 1.58 4.09 4269: fib 1.00 1.52 1.34 1.22 0.86 1.74 2.99 4.30 4270: @end example 4271: 4272: You may find the good performance of Gforth compared with the systems 4273: written in assembly language quite surprising. One important reason for 4274: the disappointing performance of these systems is probably that they are 4275: not written optimally for the 486 (e.g., they use the @code{lods} 4276: instruction). In addition, Win32Forth uses a comfortable, but costly 4277: method for relocating the Forth image: like @code{cforth}, it computes 4278: the actual addresses at run time, resulting in two address computations 4279: per NEXT (@pxref{System Architecture}). 4280: 4281: Only Eforth with the peephole optimizer performs comparable to 4282: Gforth. The speedups achieved with peephole optimization of threaded 4283: code are quite remarkable. Adding a peephole optimizer to Gforth should 4284: cause similar speedups. 4285: 4286: The speedup of Gforth over PFE, ThisForth and TILE can be easily 4287: explained with the self-imposed restriction to standard C, which makes 4288: efficient threading impossible (however, the measured implementation of 4289: PFE uses a GNU C extension: @ref{Global Reg Vars, , Defining Global 4290: Register Variables, gcc.info, GNU C Manual}). Moreover, current C 4291: compilers have a hard time optimizing other aspects of the ThisForth 4292: and the TILE source. 4293: 4294: Note that the performance of Gforth on 386 architecture processors 4295: varies widely with the version of @code{gcc} used. E.g., @code{gcc-2.5.8} 4296: failed to allocate any of the virtual machine registers into real 4297: machine registers by itself and would not work correctly with explicit 4298: register declarations, giving a 1.3 times slower engine (on a 486DX2/66 4299: running the Sieve) than the one measured above. 4300: 4301: In @cite{Translating Forth to Efficient C} by M. Anton Ertl and Martin 4302: Maierhofer (presented at EuroForth '95), an indirect threaded version of 4303: Gforth is compared with Win32Forth, NT Forth, PFE, and ThisForth; that 4304: version of Gforth is 2\%@minus{}8\% slower on a 486 than the version 4305: used here. The paper available at 4306: @*@file{}; 4307: it also contains numbers for some native code systems. You can find 4308: numbers for Gforth on various machines in @file{Benchres}. 4309: 4310: @node Bugs, Origin, Internals, Top 4311: @chapter Bugs 4312: 4313: Known bugs are described in the file BUGS in the Gforth distribution. 4314: 4315: If you find a bug, please send a bug report to 4316: @code{bug-gforth@@gnu.ai.mit.edu}. A bug report should 4317: describe the Gforth version used (it is announced at the start of an 4318: interactive Gforth session), the machine and operating system (on Unix 4319: systems you can use @code{uname -a} to produce this information), the 4320: installation options (send the @code{config.status} file), and a 4321: complete list of changes you (or your installer) have made to the Gforth 4322: sources (if any); it should contain a program (or a sequence of keyboard 4323: commands) that reproduces the bug and a description of what you think 4324: constitutes the buggy behaviour. 4325: 4326: For a thorough guide on reporting bugs read @ref{Bug Reporting, , How 4327: to Report Bugs, gcc.info, GNU C Manual}. 4328: 4329: 4330: @node Origin, Word Index, Bugs, Top 4331: @chapter Authors and Ancestors of Gforth 4332: 4333: @section Authors and Contributors 4334: 4335: The Gforth project was started in mid-1992 by Bernd Paysan and Anton 4336: Ertl. The third major author was Jens Wilke. Lennart Benschop (who was 4337: one of Gforth's first users, in mid-1993) and Stuart Ramsden inspired us 4338: with their continuous feedback. Lennart Benshop contributed 4339: @file{glosgen.fs}, while Stuart Ramsden has been working on automatic 4340: support for calling C libraries. Helpful comments also came from Paul 4341: Kleinrubatscher, Christian Pirker, Dirk Zoller, Marcel Hendrix, John 4342: Wavrik, Barrie Stott and Marc de Groot. 4343: 4344: Gforth also owes a lot to the authors of the tools we used (GCC, CVS, 4345: and autoconf, among others), and to the creators of the Internet: Gforth 4346: was developed across the Internet, and its authors have not met 4347: physically yet. 4348: 4349: @section Pedigree 4350: 4351: Gforth descends from BigForth (1993) and fig-Forth. Gforth and PFE (by 4352: Dirk Zoller) will cross-fertilize each other. Of course, a significant 4353: part of the design of Gforth was prescribed by ANS Forth. 4354: 4355: Bernd Paysan wrote BigForth, a descendent from TurboForth, an unreleased 4356: 32 bit native code version of VolksForth for the Atari ST, written 4357: mostly by Dietrich Weineck. 4358: 4359: VolksForth descends from F83. It was written by Klaus Schleisiek, Bernd 4360: Pennemann, Georg Rehfeld and Dietrich Weineck for the C64 (called 4361: UltraForth there) in the mid-80s and ported to the Atari ST in 1986. 4362: 4363: Henry Laxen and Mike Perry wrote F83 as a model implementation of the 4364: Forth-83 standard. !! Pedigree? When? 4365: 4366: A team led by Bill Ragsdale implemented fig-Forth on many processors in 4367: 1979. Robert Selzer and Bill Ragsdale developed the original 4368: implementation of fig-Forth for the 6502 based on microForth. 4369: 4370: The principal architect of microForth was Dean Sanderson. microForth was 4371: FORTH, Inc.'s first off-the-shelf product. It was developped in 1976 for 4372: the 1802, and subsequently implemented on the 8080, the 6800 and the 4373: Z80. 4374: 4375: All earlier Forth systems were custom-made, usually by Charles Moore, 4376: who discovered (as he puts it) Forth during the late 60s. The first full 4377: Forth existed in 1971. 4378: 4379: A part of the information in this section comes from @cite{The Evolution 4380: of Forth} by Elizabeth D. Rather, Donald R. Colburn and Charles 4381: H. Moore, presented at the HOPL-II conference and preprinted in SIGPLAN 4382: Notices 28(3), 1993. You can find more historical and genealogical 4383: information about Forth there. 4384: 4385: @node Word Index, Node Index, Origin, Top 4386: @chapter Word Index 4387: 4388: This index is as incomplete as the manual. Each word is listed with 4389: stack effect and wordset. 4390: 4391: @printindex fn 4392: 4393: @node Node Index, , Word Index, Top 4394: @chapter Node Index 4395: 4396: This index is even less complete than the manual. 4397: 4398: @contents 4399: @bye 4400: