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Subject: FAQ: Scheme Frequently Asked Questions 1/2 [Monthly posting]

This article was archived around: 13 Aug 1997 07:19:09 GMT

All FAQs in Directory: scheme-faq
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Archive-name: scheme-faq/part1 Last-Modified: Wed Apr 30 14:13:24 1997 by Mark Kantrowitz Version: 1.30 Maintainer: Mark Kantrowitz and Barry Margolin <ai+lisp-faq@cs.cmu.edu> URL: http://www.cs.cmu.edu/Web/Groups/AI/html/faqs/lang/scheme/top.html Size: 56149 bytes, 1157 lines
;;; **************************************************************** ;;; Answers to Frequently Asked Questions about Scheme ************* ;;; **************************************************************** ;;; Written by Mark Kantrowitz and Barry Margolin ;;; scheme_1.faq This post contains part 1 of the Scheme FAQ. If you think of questions that are appropriate for this FAQ, or would like to improve an answer, please send email to us at ai+lisp-faq@cs.cmu.edu. Note that the lisp-faq mailing list is for discussion of the content of the FAQ posting only. It is not the place to ask questions about Scheme; use either the scheme@ai.mit.edu mailing list, the comp.lang.scheme newsgroup or the Scheme Digest (scheme@mc.lcs.mit.edu) for that. If a question appears frequently in one of those forums, it will get added to the FAQ list. *** Copyright: Copyright (c) 1993-94 by Mark Kantrowitz and Barry Margolin. All rights reserved. This FAQ may be freely redistributed in its entirety without modification provided that this copyright notice is not removed. It may not be sold for profit or incorporated in commercial documents (e.g., published for sale on CD-ROM, floppy disks, books, magazines, or other print form) without the prior written permission of the copyright holder. Permission is expressly granted for this document to be made available for file transfer from installations offering unrestricted anonymous file transfer on the Internet. If this FAQ is reproduced in offline media (e.g., CD-ROM, print form, etc.), a complimentary copy should be sent to Mark Kantrowitz, School of Computer Science, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA 15213-3891 USA. This article is provided AS IS without any express or implied warranty. *** Topics Covered: Topics Covered (Part 1): [1-0] What is the purpose of this newsgroup? [1-2] What is the difference between Scheme and Common Lisp? [1-3] Scheme books, introductions, documentation, periodicals, journals, and conference proceedings. [1-4] Where can I learn about implementing Scheme interpreters and compilers? [1-7] Standards for Scheme -- What are R4RS and IEEE P1178? [1-8] How do I do object-oriented programming in Scheme? [1-9] Repositories of Scheme Software [1-10] Publicly Redistributable Scheme Software [1-11] Formatting code in LaTeX (WEB and other literate programming tools) [1-12] Where can I get an implementation of Prolog in Scheme? [1-13] What does SICP, SCOOPS, R4RS, CAR, CDR, ... mean? [1-14] Why is there no EVAL in Scheme? [1-15] World-Wide Web (WWW) Resources [1-16] Why is Scheme called 'Scheme'? Topics Covered (Part 2): [2-1] Free Scheme implementations. [2-2] Commercial Scheme implementations. [2-3] What Scheme-related discussion groups and mailing lists exist? Search for \[#\] to get to question number # quickly. *** Recent Changes: ;;; 1.19: ;;; 20-OCT-94 mk Added FTP location for Scheme84. ;;; 3-NOV-94 mk FTP collections on altdorf.ai.mit.edu have moved to ;;; swiss-ftp.ai.mit.edu ;;; 3-NOV-94 mk Added Christian Queinnec's Lisp book to [1-4]. ;;; ;;; 1.20: ;;; 15-NOV-94 mk Updated location of Ken Dickey article. ;;; ;;; 1.21: ;;; 22-NOV-94 mk Scheme Repository at Indiana University WWW page. ;;; 7-DEC-94 mk Updated EdScheme entry in [2-2]. ;;; ;;; 1.22: ;;; 16-JAN-95 mk Updated Schemers entry. ;;; 31-JAN-95 mk Added Manis' book to [1-3]. ;;; ;;; 1.23: ;;; 13-MAR-95 mk Updated EdScheme and 3DScheme for Windows in part 2. ;;; 7-APR-95 mk Added Scsh entry provided by Olin Shivers to [2-1]. ;;; ;;; 1.24: ;;; 14-APR-95 mk Updated description of the Schemer's Guide. ;;; ;;; 1.25: ;;; 13-JUL-95 mk Updated 3d-Scheme entry in part 2. ;;; ;;; 1.26: ;;; 17-AUG-95 mk Updated ELK entry in part 2. ;;; 11-SEP-95 mk Updated EdScheme and 3DScheme for Windows entries in part ;;; 2. ;;; 19-FEB-96 mk Updated Schemer's entry in part 2. ;;; 19-MAR-96 mk Added entry on comp.lang.scheme.scsh to part 2. ;;; 13-NOV-96 mk Added entry for MzScheme. ;;; 30-APR-97 mk Added Inlab Scheme to [2-2]. *** Introduction: Certain questions and topics come up frequently in the various network discussion groups devoted to and related to Scheme. This file/article is an attempt to gather these questions and their answers into a convenient reference for Scheme programmers. It (or a reference to it) is posted periodically. The hope is that this will cut down on the user time and network bandwidth used to post, read and respond to the same questions over and over, as well as providing education by answering questions some readers may not even have thought to ask. This is not a Scheme tutorial, nor is it an exhaustive list of all Scheme intricacies. Scheme is a very powerful and expressive language, but with that power comes many complexities. This list attempts to address the ones that average Scheme programmers are likely to encounter. If you are new to Scheme, see the answer to the question "How can I learn Scheme?" [1-3]. The latest version of this file is available via anonymous FTP from CMU: To obtain the files from CMU, connect by anonymous FTP to ftp.cs.cmu.edu:/user/ai/pubs/faqs/scheme/ [] using username "anonymous" and password "name@host" (substitute your email address) or via AFS in the Andrew File System directory /afs/cs.cmu.edu/project/ai-repository/ai/pubs/faqs/scheme/ and get the files scheme_1.faq and scheme_2.faq. You can also obtain a copy of the FAQ by sending a message to ai+query@cs.cmu.edu with Send Scheme FAQ in the message body. An automatically generated HTML version of the Scheme FAQ is accessible by WWW as part of the AI-related FAQs Mosaic page. The URL for this resource is http://www.cs.cmu.edu/Web/Groups/AI/html/faqs/top.html The direct URL for the Lisp FAQ is http://www.cs.cmu.edu/Web/Groups/AI/html/faqs/lang/scheme/top.html We've tried to minimize the overlap with the FAQ postings to the comp.lang.lisp, comp.lang.clos and comp.ai newsgroups, so if you don't find what you're looking for here, we suggest you try the FAQs for those newsgroups. These FAQs should be available by anonymous ftp from rtfm.mit.edu:/pub/usenet/news.answers/ [] in the lisp-faq/, ai-faq/ and scheme-faq/ subdirectories or by email. For instructions on email retrieval, send a mail message to mail-server@rtfm.mit.edu with "help" and "index" on separate lines in the body of the message. If you need to cite the FAQ for some reason, use the following format: Mark Kantrowitz and Barry Margolin, "Answers to Frequently Asked Questions about Scheme", comp.lang.scheme, <month>, <year>, ftp.cs.cmu.edu:/user/ai/pubs/faqs/scheme/scheme_?.faq, ai+lisp-faq@cs.cmu.edu. ---------------------------------------------------------------- Subject: [1-0] What is the purpose of this newsgroup? The newsgroup comp.lang.scheme exists for general discussion of topics related to the programming language Scheme. For example, possible topics can include (but are not necessarily limited to): announcements of Scheme books and products discussion of programs and utilities written in Scheme discussion of portability issues questions about possible bugs in Scheme implementations problems porting an implementation to some architecture Postings should be of general interest to the Scheme community. See also question [2-3]. The comp.lang.scheme newsgroup is archived in ftp.cs.cmu.edu:/user/ai/pubs/news/comp.lang.scheme/ on a weekly basis. Questions about Common Lisp should be directed to the newsgroup comp.lang.lisp. Discussion of object oriented programming in Lisp to the newsgroup comp.lang.clos. Discussion of functional programming language issues in general should be directed to the newsgroup comp.lang.functional. Discussion of AI programs implemented in Scheme should sometimes be cross-posted to the newsgroup comp.ai. ---------------------------------------------------------------- Subject: [1-2] What is the difference between Scheme and Common Lisp? Scheme is a dialect of Lisp that stresses conceptual elegance and simplicity. It is specified in R4RS and IEEE standard P1178. (See question [1-7] for details on standards for Scheme.) Scheme is much smaller than Common Lisp; the specification is about 50 pages, compared to Common Lisp's 1300 page draft standard. (See the Lisp FAQ for details on standards for Common Lisp.) Advocates of Scheme often find it amusing that the entire Scheme standard is shorter than the index to Guy Steele's "Common Lisp: the Language, 2nd Edition". Scheme is often used in computer science curricula and programming language research, due to its ability to represent many programming abstractions with its simple primitives. Common Lisp is often used for real world programming because of its large library of utility functions, a standard object-oriented programming facility (CLOS), and a sophisticated condition handling system. See question [1-8] for information about object-oriented programming in Scheme. In Common Lisp, a simple program would look something like the following: (defun fact (n) (if (< n 2) 1 (* n (fact (1- n))))) In Scheme, the equivalent program would like like this: (define fact (lambda (n) (if (< n 2) 1 (* n (fact (- n 1)))))) Experienced Lisp programmers might write this program as follows in order to allow it to run in constant space: (defun fact (n) (labels ((tail-recursive-fact (counter accumulator) (if (> counter n) accumulator (tail-recursive-fact (1+ counter) (* counter accumulator))))) (tail-recursive-fact 1 1))) Whereas in Scheme the same computation could be written as follows: (define fact (lambda (n) (letrec ((tail-recursive-fact (lambda (counter accumulator) (if (> counter n) accumulator (tail-recursive-fact (+ counter 1) (* counter accumulator)))))) (tail-recursive-fact 1 1)))) or perhaps (using IEEE named LETs): (define fact (lambda (n) (let loop ((counter n) (accumulator 1)) (if (< counter 2) accumulator (loop (- counter 1) (* accumulator counter)))))) Some Schemes allow one to use the syntax (define (fact n) ...) instead of (define fact (lambda (n) ...)). ---------------------------------------------------------------- Subject: [1-3] Scheme books, introductions, documentation, periodicals, journals, and conference proceedings. Introductions to Scheme: The following four books from MIT Press are listed in order of increasing difficulty. The first is good for the complete novice, the second for students with little or no previous exposure to programming, and the third and fourth for more advanced students. The third and fourth may also be used to learn a variety of powerful programming language concepts. One of these books will suit your needs. 1. Daniel P. Friedman and M. Felleisen. "The Little LISPer" MIT Press (Cambridge, MA), 3rd printing, 1989. ISBN 0-262-56038-0. Science Research Associates (Chicago), 3rd ed, 1989. 206 pages. Good for a quick introduction. Uses Scheme instead of Common Lisp. (The book uses a dialect of Scheme with footnotes about translating to Scheme or Common Lisp. The footnotes won't allow a non-expert to use Common Lisp for the advanced chapters because of the complexity.) 2. Brian Harvey and Matthew Wright "Simply Scheme: Introducing Computer Science" MIT Press, Cambridge, MA, 1994. 583 pages. ISBN 0-262-08226-8. $49.95. This book is ideal for students with little or no previous exposure to programming. The book is designed to be used before SICP (the authors call it a SICP "prequel"), and makes Scheme fun by sheltering the students from potentially confusing technical details. Unlike Pascal or C, the emphasis is on ideas, not obscure matters of syntax and arbitrary rules of style. High schools who have shied away from using Scheme because they found SICP to be too challenging should consider using this book instead. The text gradually and gently introduces students to some of the key concepts of programming in Scheme. It starts off with functions and function composition and continues with the notion of functions as data (first-class functions) and programs that write programs (higher-order functions). Since the complexity of the language is hidden, students can get involved in some of the more interesting and fun aspects of the language earlier than in other texts. Then the book progresses through the more complicated concepts of lambda, recursion, data abstraction and procedural abstraction, and concludes with sequential techniques, but with careful attention to topics students often find difficult. There are five chapters on recursion alone! There's also a pitfalls section at the end of most chapters to help students recognize and avoid common errors. The book uses several programs as examples, including a tic-tac-toe program, a pattern matcher, a miniature spreadsheet, and a simple database program. Source code for the programs is available by anonymous ftp from anarres.cs.berkeley.edu:/pub/scheme/, or for $10 on IBM or Macintosh diskettes from the publisher. 3. Harold Abelson and Gerald Jay Sussman, with Julie Sussman. "Structure and Interpretation of Computer Programs" MIT Press (Cambridge, MA) and McGraw-Hill (New York), 1985. 542 pages. ISBN 0-262-01077-1, $55. The teacher's manual, which is also available from MIT Press (ISBN 0-262-51046-4 $20), does NOT contain solutions to the exercises, but does contain hints on teaching with the book. Starts off introductory, but rapidly gets into powerful Lisp-particular constructs, such as using closures, building interpreters, compilers and object-oriented systems. Often referred to by its acronym, SICP, which is pronounced "Sick-Pee". This is the classical text for teaching program design using Scheme, and everybody should read it at least once. MIT problem sets are available from the repositories, and materials from Gustavus Adolphus College are available from ftp.gac.edu:/pub/SICP/. 4. George Springer and Daniel P. Friedman "Scheme and the Art of Programming" MIT Press and McGraw Hill, 1990, 596 pages. ISBN 0-262-19288-8, $50. Introduces basic concepts of programming in Scheme. Also deals with object oriented programming, co-routining, continuations. Gives numerous examples. Has more of an emphasis on teaching Scheme than SICP, and can be seen as an alternative to SICP. Source code from the chapters is available from ftp.cs.indiana.edu:/pub/scheme-repository/doc/lit/sap/ 5. Iain Ferguson, Edward Martin and Burt Kaufman. Foreword by Daniel Friedman. "The Schemer's Guide: Second Edition" Schemers Inc., Ft. Lauderdale, FL, 1995. (see EdScheme entry in [2-2]) 330 pages, ISBN 0-9628745-2-3, $35.95. This book assumes no previous programming experience and is ideal for high school or college students. The book presents the elements of modern computer programming in an easy-to-follow and entertaining manner. It gently introduces students to the Scheme programming language, guiding them through such concepts as functional programming, recursion, data structures, higher order functions, delayed evaluation, and object-oriented programming. The text concludes with a significant game-playing project involving artificial intelligence. The book strikes a good balance between theory and practice, while nurturing good programming practices. The Schemer's Guide has a proven track record of several years use in teaching the art of Scheme programming to high school students and college undergraduates. A comprehensive teacher's guide and an additional set of resource materials including worksheets, quizzes, projects, and exams are available to instructors using this text. (A Spanish translation will be available by August 1995.) Older Introductions to Scheme: 1. Smith, Jerry D. "Introduction to Scheme" Prentice Hall (Englewood Cliffs, NJ), 1988, 324 pages. Focuses on PC Scheme. 2. Michael Eisenberg "Programming in Scheme" Scientific Press (Redwood City, CA), 1988. 304 pages. 3. Two articles in BYTE Magazine, February 1988, by Abelson and Sussman, and Clinger. Online Introductions to Scheme: 1. The Ken Dickey article, "The Scheme Programming Language", in COMPUTER LANGUAGES magazine, June 1992, is available from the Scheme Repository at ftp.cs.indiana.edu:/pub/scheme-repository/doc/pubs/intro.txt The Revised^4 Report on the Algorithmic Language Scheme is also available from the Scheme Repository. 2. The Info files from the MIT Scheme implementation. ftp.cs.indiana.edu:/pub/scheme-repository/imp/MIT-Scheme-7.3/doc 3. "Introductory Scheme" by Joseph W. Lavinus and James D. Arthur, <lavinus@virginia.edu>. Available from the Lisp Utilities Repository as ftp.cs.cmu.edu:/user/ai/lang/scheme/doc/intro/ as scmintro.tgz. Scheme and Artificial Intelligence: 1. Wolfgang Kreutzer and Bruce McKenzie "Programming for Artificial Intelligence: Methods, Tools and Applications" Addison-Wesley (Reading, MA), 1990. 682 pages. ISBN 0-201-41621-2. Discusses Scheme, Prolog, and Smalltalk, gives an overview of the history and philosophy of AI, surveys three major programming paradigms (procedural, declarative, and object-oriented), and metaphors to AI programming. Source code from the chapters is available from ftp.cs.indiana.edu:/pub/scheme-repository/lit/ as aibook.tar.Z. Some of the programs will only run under MacScheme. Scheme-based Computer Science Texts: 1. Vincent Manis and James Little "The Schematics of Computation" Prentice-Hall, Inc., 1995. 848 pages ISBN 0-13-834284-9 (North America), $41 ISBN 0-13-433772-7 (International). For a copy of the publication announcement, see ftp.cs.cmu.edu:/user/ai/pubs/books/announce/manis95 General Scheme reference books include: 1. K. Dybvig "The Scheme programming language" Prentice Hall, 1987. Good reference for Scheme. Scheme-related periodicals include: 1. LISP Pointers. Published by ACM SIGPLAN six times a year. Volume 1, Number 1 was April-May 1987. Subscriptions: ACM Members $12; ACM Student Members $7; Non-ACM members $25. Mail checks payable to the ACM to ACM Inc., PO Box 12115, Church Street Station, New York, NY 10249. 2. LISP and Symbolic Computation, Kluwer Academic Press. Volume 1 was published in 1989. (jlz@lucid.com is the editor). ISSN 0892-4635. Subscriptions: Institutions $169; Individuals $80. Add $8 for air mail. Kluwer Academic Publishers, PO Box 322, 3300 AH Dordrecht, The Netherlands, or Kluwer Academic Publishers, PO Box 358, Accord Station, Hingham, MA 02018-0358. 3. Proceedings of the biannual ACM Lisp and Functional Programming Conference. (First one was in 1980.) 4. Proceedings of the annual Lisp Users and Vendors Conference. See also the Scheme Bibliography from the Scheme Repository (ftp.cs.indiana.edu:/pub/scheme-repository/) for additional readings. A large number of technical reports on Scheme are now available in the text section (ftp.cs.indiana.edu:/pub/scheme-repository/txt/). ---------------------------------------------------------------- Subject: [1-4] Where can I learn about implementing Scheme interpreters and compilers? There is no single book that is really comprehensive, so you will have to combine reading the sources to the various free implementations (e.g., Gambit [Feeley] and S48 [Rees]) with bits and pieces of tech reports and various books. Books about Scheme implementation include: 1. John Allen "Anatomy of Lisp" McGraw-Hill, 1978. 446 pages. ISBN 0-07-001115-X 2. Samuel Kamin "Programming Languages, An Interpreter-Based Approach" Addison-Wesley, Reading, Mass., 1990. ISBN 0-201-06824-9 Includes sources to several interpreters for Lisp-like languages, and a pointer to sources via anonymous ftp. 3. Sharam Hekmatpour "Lisp: A Portable Implementation" Prentice Hall, 1985. ISBN 0-13-537490-X. Describes a portable implementation of a small dynamic Lisp interpreter (including C source code). 4. Peter Henderson "Functional Programming: Application and Implementation" Prentice-Hall (Englewood Cliffs, NJ), 1980. 355 pages. 5. Peter M. Kogge "The Architecture of Symbolic Computers" McGraw-Hill, 1991. ISBN 0-07-035596-7. Includes sections on memory management, the SECD and Warren Abstract Machines, and overviews of the various Lisp Machine architectures. 6. Daniel P. Friedman, Mitchell Wand, and Christopher T. Haynes "Essentials of Programming Languages" MIT Press, 1992, 536 pages. ISBN 0-262-06145-7, $55. Teaches fundamental concepts of programming language design by using small interpreters as examples. Covers most of the features of Scheme. Includes a discussion of parameter passing techniques, object oriented languages, and techniques for transforming interpreters to allow their implementation in terms of any low-level language. Also discusses scanners, parsers, and the derivation of a compiler and virtual machine from an interpreter. Source files available by anonymous ftp from ftp.cs.indiana.edu:/pub/eopl/ ( or from the Scheme Repository in ftp.cs.indiana.edu:/pub/scheme-repository/doc/lit/eopl 7. Peter Lee, editor, "Topics in Advanced Language Implementation", The MIT Press, Cambridge, Mass., 1991. Articles relevant to the implementation of functional programming languages. 8. Also see the proceedings of the biannual ACM Lisp and Functional Programming conferences, the implementation notes for CMU Common Lisp, Peter Norvig's book ("Paradigms of AI Programming: Case Studies in Common Lisp", Morgan Kaufmann, 1992. 946 pages. ISBN 1-55860-191-0), and SICP (Abelson & Sussman). 9. Christian Queinnec "Les Langages Lisp" InterEditions (in French), 1994. 500 pages. ISBN 2-7296-0549-5, 61-2448-1. (?) The book covers Lisp, Scheme and other related dialects, their interpretation, semantics and compilation. All of the programs described in the book are available by anonymous ftp from ftp.inria.fr:/INRIA/Projects/icsla/Books/LiSP94Sep05.tar.gz For more information, see the book's URL file://ftp.inria.fr/INRIA/Projects/icsla/WWW/LiSP.html or contact the author at Christian.Queinnec@inria.fr Technical reports and journal articles about Scheme implementation include: Mitchell Wand and Daniel P. Friedman, "Compiling Lambda Expressions Using Continuations and Factorizations", Journal of Computer Languages 3(1978), 241-263. Guy Lewis Steele Jr., "Rabbit: A Compiler for Scheme", MIT AI Memo 474, Massachusetts Institute of Technology, Cambridge, MA, May 1978. Guy Lewis Steele Jr., "Compiler Optimization Based on Viewing LAMBDA as RENAME + GOTO", in "Artificial Intelligence: An MIT Perspective", Patrick Henry Winston and Richard Henry Brown (eds.), MIT Press, Cambridge, MA, 1980. Jonathan A. Rees and Norman I. Adams, "T: A Dialect of Lisp or, LAMBDA: The Ultimate Software Tool", Conference Record of the 1982 ACM Symposium on Lisp and Functional Programming, 1982, 114-122. R. Kent Dybvig, "C-Scheme", Computer Science Department Technical Report #149 (MS Thesis), Indiana University, Bloomington, IA, 1983. William Clinger, "The Scheme 311 compiler: An Exercise in Denotational Semantics", Conference Record of the 1984 ACM Symposium on Lisp and Functional Programming, 1984, 356-364. Guillermo J. Rozas, "Liar, an Algol-like Compiler for Scheme", S.B. Thesis, Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, January 1984. David H. Bartley and John C. Jensen, "The Implementation of PC Scheme", Proceedings of the 1986 ACM Conference on Lisp and Functional Programming, 1986, 86-93. David Kranz, Richard Kelsey, Jonathan A. Rees, Paul Hudak, James Philbin and Norman I. Adams, "Orbit: An Optimizing Compiler for Scheme", Proceedings of the SIGPLAN Notices '86 Symposium on Compiler Construction, June 1986, 219-233. Published as SIGPLAN Notices 21(7), July 1986. Marc Feeley, "Deux Approches a' L'implantation du Language Scheme", M.Sc. Thesis, De'partement d'Informatique et de Recherche Ope'rationelle, University of Montreal, May 1986. R. Kent Dybvig, "Three Implementation Models for Scheme", Department of Computer Science Technical Report #87-011 (Ph.D. Dissertation), University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, April 1987. William D. Clinger, Anne H. Hartheimer and Eric M. Ost, "Implementation Strategies for Continuations", Conference Record of the 1988 ACM Conference on Lisp and Functional Programming, August 1988, 124-131. David Kranz, "Orbit: An Optimizing Compiler for Scheme", Computer Science Technical report #632 (Ph.D. Dissertation), Yale University, 1988. Joel F. Bartlett, "SCHEME->C a Portable Scheme-to-C Compiler", Research Report 89/1, Dec. Western Research Laboratory, Palo Alto, CA, January 1989. Marc Feeley and James S. Miller, "A Parallel Virtual Machine for Efficient Scheme Compilation", Proceedings of the 1990 ACM Conference on Lisp and Functional Programming, Nice, France, June 1990. Chris Hanson, "Efficient Stack Allocation for Tail-Recursive Languages", Proceedings of the 1990 ACM Conference on Lisp and Functional Programming, Nice, France, June 1990. Robert Hieb, R. Kent Dybvig and Carl Bruggeman, "Representing Control in the Presence of First-Class Continuations", Proceedings of the SIGPLAN Notices '90 Conference on Programming Language Design and Implementation, White Plains, New York, June 1990, 66-77. Guillermo Rozas, "Taming the Y Operator", Proceedings of the 1992 ACM Conference on Lisp and Functional Programming, San Francisco, CA, June 1992, 226-234. Dan Teodosiu, "HARE: An Optimizing Portable Compiler for Scheme", ACM Sigplan Notices 26(1), January 1991. ---------------------------------------------------------------- Subject: [1-7] Standards for Scheme -- What are R4RS and IEEE P1178? R4RS is the Revised^4 Report on the Algorithmic Language Scheme, edited by W. Clinger and J. Rees. It appeared in ACM Lisp Pointers IV, July-September 1991, and also as MIT AI Memo 848b. It serves as a kind of standard for the language. It can be obtained by anonymous ftp at the two Scheme Repositories, swiss-ftp.ai.mit.edu and ftp.cs.indiana.edu. A HTML version is available as ftp://swiss-ftp.ai.mit.edu/pub/scm/HTML/r4rs_toc.html or http://www.maths.tcd.ie/scrg/scheme/index.html IEEE P1178 is IEEE Standard 1178-1990, "IEEE Standard for the Scheme Programming Language", published by IEEE in 1991. ISBN 1-55937-125-0. It is now also an ANSI standard. It may be ordered from IEEE by calling 1-800-678-IEEE or 908-981-1393 or writing IEEE Service Center, 445 Hoes Lane, P.O. Box 1331, Piscataway, NJ 08855-1331, and using order number SH14209 ($28 for IEEE members, $40 others). ---------------------------------------------------------------- Subject: [1-8] How do I do object-oriented programming in Scheme? Some Scheme implementations (for example, MacScheme, Feel, Oaklisp, XScheme, and PC-Scheme) include built-in object-oriented extensions. BOS (Bryan's Object System) is a very small object system for Scheme. It is based around generic functions and multiple inheritance. BOS provides more or less the same features as Meroon and the Tiny CLOS base language. Even though it has not been optimised, it should be quite a bit faster than those because it does not include a MOP. BOS has been tested under Scheme 48 and SCM, and should run under any fairly modern Scheme implementation (especially any which runs SLIB) with little or no change. It is available by anonymous ftp from ftp.maths.tcd.ie:/pub/bosullvn/misc/bos.tar.gz and the CMU AI Repository in ftp.cs.cmu.edu:/user/ai/lang/scheme/oop/bos/ For more information, write to Bryan O'Sullivan <bosullvn@maths.tcd.ie>. MEROON is a package written in Scheme to provide the basic facilities of an object-oriented programming style through three macros: define-class, define-generic, and define-method. MEROON offers simple inheritance, reflective metaclasses and simple dispatching generic functions with support for multimethods. MEROON also offers indexed fields subsuming Scheme vectors without inheritance restrictions. Meroon runs in Scheme->C, PC-Scheme, Chez Scheme, Elk, Bigloo, SCM with SLIB, and MacGambit. MEROON sources and documentation may be found in the Scheme Repository as ftp.cs.indiana.edu:/pub/scheme-repository/new/meroon.*.tar.Z and also from ftp.inria.fr:/pub/INRIA/icsla/Programs/MeroonV3*.tar.gz [] The file meroonet*.tar.gz is a toy version of meroon. For more information, contact Christian Queinnec <queinnec@polytechnnique.fr> or <Christian.Queinnec@inria.fr>. SCOOPS (Scheme Object Oriented Programming System) is an object system for Scheme written by Amitabh Srivastava/Texas Instruments with re-writes by Steve Sherin <sherin@linc.cis.upenn.edu>. [Email to this address bounced 7/7/93.] This package needs first-class environments. It is available from the Scheme Repository as /pub/scheme-repository/scm/scoops.sha. Tiny CLOS is a Scheme implementation of a `kernelized' CLOS, with a metaobject protocol. The implementation is even simpler than the simple CLOS found in `The Art of the Metaobject Protocol,' weighing in at around 850 lines of code, including (some) comments and documentation. Tiny CLOS is available by anonymous ftp from parcftp.xerox.com:/pub/mops/. Tiny CLOS runs in MIT Scheme 11.74 and should run with only minor modifications in other Schemes as well. If you want to be added to the mops@parc.xerox.com mailing list (technical questions and discussion only), send mail to Gregor Kiczales <gregor@parc.xerox.com>. YASOS (Yet Another Scheme Object System) is fairly functional in style and uses delegation. The implementation includes multiple inheritance and "send to super" and is much smaller than class-based OO systems. See Ken Dickey, "Scheming with Objects", AI Expert 7(10):24-33, October 1992. A copy of the article and YASOS code is available from the Scheme Repository in pub/scheme-repository/txt/swob.txt. YASOS is also included as part of SLIB. For further information, contact Ken Dickey <kend@newton.apple.com>. ---------------------------------------------------------------- Subject: [1-9] Repositories of Scheme Software There are several repositories of publicly redistributable and public domain Scheme code. CMU AI Repository, Scheme Section: The Scheme Section of the CMU Artificial Intelligence Repository is accessible by anonymous ftp to ftp.cs.cmu.edu:/user/ai/lang/scheme/ [] through the AFS directory /afs/cs.cmu.edu/project/ai-repository/ai/lang/scheme/ or by WWW from the URL http://www.cs.cmu.edu/Web/Groups/AI/html/repository.html and includes more than 200 megabytes of sources and other materials of interest to Scheme programmers, including all freely distributable implementations and many programs. Unlike the Scheme Repository at Indiana University, the entire contents of the CMU AI Repository has been keyword indexed to provide convenient browsing of the contents. The repository has standardized on using 'tar' for producing archives of files and 'gzip' for compression. To search the keyword index by mail, send a message to: ai+query@cs.cmu.edu with one or more lines containing calls to the keys command, such as: keys scheme awk in the message body. Keywords may be regular expressions and are compared with the index in a case-insensitive conjunctive fashion. You'll get a response by return mail. Do not include anything else in the Subject line of the message or in the message body. For help on the query mail server, include: help instead. A Mosaic interface to the keyword searching program is in the works. We also plan to make the source code (including indexes) to this program available, as soon as it is stable. Most of the Scheme Section of the AI Repository appears on Prime Time Freeware for AI, Issue 1-1, a mixed-media book/CD-ROM publication. It includes two ISO-9660 CD-ROMs bound into a 224 page book and sells (list) for US$60 plus applicable sales tax and shipping and handling charges. Payable through Visa, Mastercard, postal money orders in US funds, and checks in US funds drawn on a US bank. For more information write to Prime Time Freeware, 370 Altair Way, Suite 150, Sunnyvale, CA 94086 USA, call 408-433-9662, 408-433-0727 (fax), or send email to ptf@cfcl.com. Contributions of software and other materials are always welcome but must be accompanied by an unambiguous copyright statement that grants permission for free use, copying, and distribution -- either a declaration by the author that the materials are in the public domain, that the materials are subject to the GNU General Public License (cite version), or that the materials are subject to copyright, but the copyright holder grants permission for free use, copying, and distribution. (We will tell you if the copying permissions are too restrictive for us to include the materials in the repository.) Inclusion of materials in the repository does not modify their copyright status in any way. Materials may be placed in: ftp.cs.cmu.edu:/user/ai/new/ When you put anything in this directory, please send mail to ai+contrib@cs.cmu.edu giving us permission to distribute the files, and state whether this permission is just for the AI Repository, or also includes publication on the CD-ROM version (Prime Time Freeware for AI). We would also appreciate if you would include a 0.doc file for your package; see /user/ai/new/package.doc for a template. (If you don't have the time to write your own, we can write it for you based on the information in your package.) The Scheme Section of the AI Repository is maintained by Mark Kantrowitz <AI.Repository@cs.cmu.edu>. Scheme Repository at Indiana University: The Scheme Repository at Indiana University contains a Scheme bibliography, copies of the R4RS report and other papers, sample Scheme code for a variety of purposes, several utilities, and some implementations. The Scheme code includes code for calendar calculations, Earley parser, FORMAT for Scheme, a scheme version of the Gabriel benchmarks, Marc Feeley's minimal object support for Scheme, a Scheme pretty-printer, a Prolog interpreter written in Scheme, a random number generator in Scheme, an implementation of SCOOPS, code from Abelson and Sussman's SICP book, Aubrey Jaffer's IEEE/R4RS compliance test, an implementation of matrices, a Scheme implementation of the Common Lisp FORMAT function, a Scheme front end to Adobe Illustrator PostScript, and a LALR(1) parser (ZEBU). The repository was established by Ozan S. Yigit and is currently maintained by David Eby and John Zuckerman. Send administrative requests to scheme-repository-request@cs.indiana.edu The repository is accessible by anonymous ftp at ftp.cs.indiana.edu:/pub/scheme-repository/ [] or by WWW to http://www.cs.indiana.edu/scheme-repository/home.html The repository is mirrored in INRIA, courtesy of Christian Queinnec [Ecole Polytechnique and INRIA-Rocquencourt], ftp.inria.fr:/lang/Scheme/ and also faui80.informatik.uni-erlangen.de:/pub/scheme/yorku Other Scheme Collections: Scheme Implementations may also be found at swiss-ftp.ai.mit.edu:/archive/ The R4RS report is available in swiss-ftp.ai.mit.edu:/archive/scheme-reports/ or as MIT AI Memo 848b (email publications@ai.mit.edu for more information). The swiss-ftp archive includes SCOOPS, CL2Scheme, extend-syntax, btree, Gabriel benchmarks, FORMAT for Scheme, etc. The GI (German Computer Science Society) Scheme Archive contains a variety of scheme programs, utilities, code from theses, and other materials. It also mirrors the Scheme Repository. It is accessible by anonymous ftp to faui80.informatik.uni-erlangen.de (login as 'ftp', giving your email address as the password). pub/scheme/gi # GI Scheme Archive pub/scheme/yorku # Internet Scheme Repository Direct questions to scheme@faui80.informatik.uni-erlangen.de. The GI Scheme Archive is supported by the German Computer Society Special Interest Group on AI programming and sponsored by the Bavarian AI Center FORWISS -- Research Institute for Knowledge Based Systems. ---------------------------------------------------------------- Subject: [1-10] Publicly Redistributable Scheme Software SLIB (Standard Scheme Library) is a portable scheme library that provides compatibility and utility functions for many of the standard scheme implementations, including Chez, ELK 2.1, GAMBIT, MITScheme, scheme->C, Scheme48, T3.1, VSCM and Scm4e. It is available by anonymous ftp from swiss-ftp.ai.mit.edu:/archive/scm/slib2a1.tar.gz prep.ai.mit.edu:/pub/gnu/jacal/slib2a1.tar.gz ftp.cs.indiana.edu:/pub/scheme-repository/new/slib2a1.tar.gz Now includes a FAQ file. TEST.SCM is an IEEE and R4RS conformance test suite. It is available from swiss-ftp.ai.mit.edu:/archive/scm/test.scm prep.ai.mit.edu:/pub/gnu/jacal/test.scm ftp.cs.indiana.edu:/pub/scheme-repository/new/test.scm PSD (Portable Scheme Debugger) is available by anonymous ftp from Tampere University of Technology, Finland, ftp.cs.tut.fi:/pub/src/languages/schemes/psd-1.1.tar.Z With PSD, you can run a Scheme program in an Emacs buffer, set breakpoints, single step evaluation and access and modify the program's variables. It works by instrumenting the original source code, so it should run with any R4RS compliant Scheme. It has been tested with SCM and Elk 1.5, but should work with other Schemes with a minimal amount of porting, if at all. Includes documentation and user's manual. Written by Pertti Kellom\"aki, pk@cs.tut.fi The Lisp Pointers article describing PSD (Lisp Pointers VI(1):15-23, January-March 1993) is available as http://www.cs.tut.fi/staff/pk/scheme/psd/article/article.html SCLINT is a lint-like program for Scheme. It checks for consistency of indentation, syntax of special forms, and the number of arguments to primitive and most user-defined procedures. This is not a full implementation, but rather a quick hack. It is used in teaching programming at the Tampere University of Technology. It is available by anonymous ftp from ftp.cs.tut.fi:/pub/src/languages/schemes/sclint-0.9.tar.Z. For further information, write to Pertti Kellom\"aki <pk@cs.tut.fi>. A bibliography of work in functional programming can be obtained by anonymous ftp from tamdhu.dcs.st-andrews.ac.uk:/pub/staple/pubs.txt ( It uses a refer-like format with %T for title, %A for authors %I for a unique index entry %S for source (possibly a reference to another index) %K for keywords and %C for comments. Compiled by Tony Davie, <ajtd@honey.st-and.ac.uk>. [Email bounced, 7/7/93.] Scheme Utilities -- brokaw.lcs.mit.edu:/pub/scmutils.tar [This collection seems to no longer be located on brokaw -- does anybody know the current location?] A collection of Scheme implementations of data structures and algorithms is available by anonymous ftp from ftp.cs.tut.fi:/pub/src/languages/schemes/ as the file scheme-algorithms.tar. For more information, contact Pertti Kellom\"aki <pk@cs.tut.fi>. 6.001. The User's Manual, example code, and problem sets from MIT's course "Structure and Interpretation of Computer Programs" are available by anonymous ftp from swiss-ftp.ai.mit.edu:/archive/6.001/ []. Steele's Constraint System. Chris Hanson's implementation of Steele's constraint system is available for anonymous ftp from swiss-ftp.ai.mit.edu:/archive/cph/constraint.tar [] ftp.cs.indiana.edu:/pub/scheme-repository/new/constraint.tar.Z A compressed version is also stored there. The software is source code for MIT Scheme. It should run in release 7.1.3. Most of the MIT Scheme dependencies could be eliminated, but it also uses the following procedures which aren't in standard Scheme: error, bkpt, macros, dynamic binding, and string output ports. The code corresponds pretty closely to Guy Steele's PhD thesis implementation, which you can obtain in printed form from the MIT AI Lab publications office as AI-TR-595 for $15.00 (email publications@ai.mit.edu for more information). For more information, send email to Chris Hanson <cph@martigny.ai.mit.edu>. JACAL is a symbolic mathematics system for the simplification and manipulation of equations and single and multiple valued algebraic expressions constructed of numbers, variables, radicals, and algebraic functions, differential, and holonomic functions. In addition, vectors and matrices of the above objects are included. JACAL is written in Scheme and requires SLIB. JACAL source is available via anonymous FTP from swiss-ftp.ai.mit.edu:/archive/scm/jacal1a4.tar.Z, prep.ai.mit.edu:/pub/gnu/jacal/jacal1a4.tar.Z, and ftp.cs.indiana.edu:/pub/scheme-repository/new/jacal1a4.tar.Z Contact jaffer@altdorf.ai.mit.edu for more information. Zebu 0.9 is an LALR(1) parser generator for Scheme written by William M. Wells III. It lives in the Scheme Repository ftp.cs.indiana.edu:/pub/scheme-repository/scm/ and works with PC-Scheme from TI and MIT C-Scheme 6.2 (but not with anything after 7.0). Thomas is a compiler for the Dylan programming language. The Thomas system is written in Scheme and runs under MIT's CScheme, DEC's Scheme->C, and Marc Feeley's Gambit. It can run on a wide range of machines including the Macintosh, PC compatibles, Vax, MIPS, Alpha, and 680x0. Thomas generates IEEE compatible Scheme code. Thomas is available to the public by anonymous ftp at crl.dec.com:/pub/DEC/Thomas gatekeeper.pa.dec.com:/pub/DEC/Thomas swiss-ftp.ai.mit.edu:/archive/Thomas For more information on Thomas and Dylan, see part 4 of the Lisp FAQ. MATCH is a pattern matching macro package for Scheme. Pattern matching allows complicated control decisions based on data structure to be expressed in a concise manner. This document describes several pattern matching macros for Scheme, and an associated mechanism for defining new forms of structured data. This macro package works with any Scheme that supports defmacro (which is obtainable by loading SLIB), such as Chez Scheme (release 4 or greater). MATCH is available by anonymous ftp from titan.cs.rice.edu:/public/wright/match.tar.Z [] and includes the macro source code and documentation. A copy should be available from the Scheme Repository shortly. For further information, write to Andrew Wright, <wright@cs.rice.edu>. Soft Scheme provides the benefits of static typing for dynamically typed Scheme. Like a static type checker, a soft type checker infers types for variables and expressions. But rather than reject programs containing untypable fragments, a soft type checker inserts explicit run-time checks to transform untypable programs to typable form. These run-time checks indicate potential program errors, enabling programmers to detect errors prior to program execution. Soft type checking minimizes the number of run-time checks in the compiled code, enabling dynamically typed languages to attain the efficiency of statically typed languages like ML. Soft Scheme is available by anonymous ftp from titan.cs.rice.edu:public/wright/softscheme.tar.Z [] For more information, write to Andrew Wright <wright@cs.rice.edu>. ChezSybase is a Chez Scheme interface to the Sybase database. It uses the Chez Scheme foreign function interface to provide a high-level Scheme interface to the Sybase db-lib (the API to the Sybase database). Most of the db-lib calls and datatypes are supported, with the possible exception of spotty support for text and image data, and there is no analog to the datetime datatype. It is available by anonymous ftp from ftp.cs.cmu.edu:/user/ai/lang/scheme/code/io/chez_syb/ For more information, write to Karl O. Pinc <kop@acm.org>. ---------------------------------------------------------------- Subject: [1-11] Formatting code in LaTeX SLaTeX is a R4RS-compliant Scheme program that allows you to write program code "as is" in your LaTeX or TeX source. It is particularly geared to the programming languages Scheme and Common Lisp, and has been tested in Chez Scheme, Common Lisp, MIT C Scheme, Elk, Scheme->C, SCM and UMB Scheme on Unix; and MIT C Scheme and SCM on MSDOS. The formatting of the code includes assigning appropriate fonts to the various tokens in the code (keywords, variables, constants, data), at the same time retaining the proper indentation when going to the non-monospace (non-typewriter) provided by TeX. SLaTeX comes with two databases that recognize the standard keywords/variables/constants of Scheme and Common Lisp respectively. These can be modified by the user using easy TeX commands. In addition, the user can inform SLaTeX to typeset arbitrary identifiers as specially suited TeX expressions (i.e., beyond just fonting them). The code-typesetting program SLaTeX is available by anonymous ftp from cs.rice.edu:/public/dorai/slatex23.tar.gz Send bug reports to dorai@cs.rice.edu. SchemeWEB provides simple support for literate programming in Lisp. SchemeWEB version 2.0 is a Unix filter that allows you to generate both Lisp and LaTeX code from one source file. The generated LaTeX code formats Lisp programs in typewriter font obeying the spacing in the source file. Comments can include arbitrary LaTeX commands. SchemeWEB was originally developed for the Scheme dialect of Lisp, but it can easily be used with most other dialects. Version 2.0 is available in the Scheme Repository as ftp.cs.indiana.edu:/pub/scheme-repository/new/schemeweb.sh or in the Comprehensive TeX Archive Network (CTAN) in the directory ftp.shsu.edu:/tex-archive/web/schemeweb The Literate Programming FAQ lists a number of alternatives, both language-independent and Scheme-specific. The Literate Programming FAQ is posted once a quarter to the comp.programming.literate newsgroup and is available by anonymous ftp from rtfm.mit.edu. A copy may also be requested by sending an email message to fileserv@shsu.edu sendme litprog.faq in the body of the message. ---------------------------------------------------------------- Subject: [1-12] Where can I get an implementation of Prolog in Scheme? Prolog in Scheme is a collection of macros that expand syntax for clauses, elations, and so on. It is written in Scheme and has support for delayed goals and interval arithmetic. It is known to run in Chez Scheme and in Elk, and is intended to be portable to other Scheme implementations. It relies on continuations, and so is not easily ported to Common Lisp. Available from the University of Calgary by anonymous ftp from ftp.cpsc.ucalgary.ca:/pub/projects/prolog1.2/prolog12.tar.Z Questions and comments may be addressed to Alan Dewar <dewar@cpsc.ucalgary.ca> or John Cleary <jcleary@waikato.ac.nz>. Schelog is an embedding of Prolog in Scheme. It represents Prolog goals as procedures in Scheme, and includes macros to simulate a Prolog-style syntax for clauses, relations and queries. The embedding permits the user to combine Prolog and Scheme code freely, in the same s-expression, if desired. Documentation and examples are included. Schelog should run in any R4RS Scheme, has been tested in SCM and Chez Scheme, and will run in any Scheme implementation that supports SLIB (see entry in [1-10] above). Schelog (version 2) is available by anonymous ftp from titan.cs.rice.edu:/public/dorai/schelog2.tar.Z. Its use of higher-order continuations is probably a major obstacle to porting it to Common Lisp. For more information, please contact the author Dorai Sitaram <dorai@cs.rice.edu>. ---------------------------------------------------------------- Subject: [1-13] What does SICP, SCOOPS, R4RS, CAR, CDR, ... mean? Glossary of acronyms: CAR Originally meant "Contents of Address portion of Register", which is what CAR actually did on the IBM 704. CDR Originally meant "Contents of Decrement portion of Register", which is what CDR actually did on the IBM 704. Pronounced "Cudder". ANSI American National Standards Institute SICP Abelson and Sussman's book "Structure and Interpretation of Computer Programs". EOPL Essentials of Programming Languages SCOOPS An experimental object-oriented programming language for Scheme. R3RS Revised^3 Report on the Algorithmic Language Scheme. R4RS Revised^4 Report on the Algorithmic Language Scheme. ---------------------------------------------------------------- Subject: [1-14] Why is there no EVAL in Scheme? The answer to this question is based on information provided by Guillermo J. Rozas and Aubrey Jaffer. There are three major positions in the Scheme community regarding EVAL: 1. No EVAL: EVAL is antithetical to a Pascal-like (compiler based, externally statically linked) implementation for Scheme, such as some people have or wish to see. 2. Single Argument: There is a single distinguished top-level environment, and EVAL always evaluates its argument there. (This is the approach taken in Common Lisp, where EVAL evaluates its argument in the current dynamic environment and in a null lexical environment.) 3. Two Arguments: There are multiple environments in which the user might want to evaluate expressions, so EVAL should take two arguments, the second being an environment. In particular, in some systems with first-class environments, there is no a-priori single distinguished top-level environment, and defaulting the environment does not fit those dialects well. Not every dialect of Scheme has EVAL. Most do, but some with different names and arguments. Jaffer's SLIB package uses LOAD as defined in R4RS to define EVAL for those implementations that don't support EVAL (e.g., by writing the code out to a file and then loading it). Rozas's compromise proposal for EVAL was accepted for R5RS, but it is unclear whether there will ever be a R5RS. ---------------------------------------------------------------- Subject: [1-15] World-Wide Web (WWW) Resources The World Wide Web (WWW) is a hypermedia document that spans the Internet. It uses the http (HyperText Transfer Protocol) for the light-weight exchange of files over the Internet. NCSA Mosaic is a World Wide Web browser developed at the National Center for Supercomputing Applications (NCSA). Mosaic's popularity derives, in part, from its ability to communicate using more traditional Internet protocols like FTP, Gopher, WAIS, and NNTP, in addition to http. Mosaic can display text, hypertext links, and inlined graphics directly. When Mosaic encounters a file type it can't handle internally, such as Postscript documents, mpeg movies, sound files, and JPEG images, it uses an external viewer (or player) like Ghostscript to handle the file. Mosaic also includes facilities for exploring the Internet. In other words, Mosaic is an multimedia interface to the Internet. The hypertext documents viewed with Mosaic are written in HTML (HyperText Markup Language), which is a subset of SGML (Standard Generalized Markup Language). All that is needed is just a few more improvements, such as the ability to format tables and mathematics, and a WYSIWYG editor, for HTML to greatly facilitate electronic journals and other publications. NCSA Mosaic for the X Window System is available by anonymous ftp from ftp.ncsa.uiuc.edu:/Mosaic/ as source code and binaries for Sun, SGI, IBM RS/6000, DEC Alpha OSF/1, DEC Ultrix, and HP-UX. Questions about NCSA Mosaic should be directed to mosaic-x@ncsa.uiuc.edu (X-Windows version), mosaic-mac@ncsa.uiuc.edu (Macintosh), and mosaic-win@ncsa.uiuc.edu (Microsoft Windows). A simple HTML version of the Scheme FAQ (this FAQ) is available as http://www.cs.cmu.edu/Web/Groups/AI/html/faqs/lang/scheme/top.html The Scheme home page at MIT is http://www-swiss.ai.mit.edu/scheme-home.html It includes a nifty little form that lets you execute small examples of Scheme code. The Scheme Underground web page is http://www.ai.mit.edu/projects/su/su.html ---------------------------------------------------------------- Subject: [1-16] Why is Scheme called 'Scheme'? According to Steele and Gabriel's "The Evolution of Lisp" paper, Scheme was originally called Schemer, in the tradition of the AI languages Planner and Conniver. But the ITS operating system had a 6-character limitation of file names, so the names were shortened to PLNR, CNVR, and SCHEME. Eventually the truncated name Scheme stuck. ---------------------------------------------------------------- ;;; *EOF*