5 - Forth Interest Group

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Published by Forth Interest Group Volume II No. 5 January/February 1981 Publisher Roy C. Martens Guest Edi tor S B Bassett Editorial Review Board Bill Ragsdale Dave Boulton Kim Harris John James Dave Kilbridge Henry Laxen George Maverick FORTH DIMENSIONS sclicits editorial material. comments and letters No responsibility is assumed for accuracy of material submitted ALL MATERIAL PUBLISHED BY THE FORTH INTEREST GROUP IS IN THE PUBLIC DOMAIN Information in FORTH DIMENSIONS may be reproduced with credit given to the author and the Forth Interest Group Subscription to FORTH DIMENSIONS is free with membership in the Forth Interest Group at $1 2 00 per year ($24 00 Overseas air) For membership. change of address and/or to submit material, the address is Forth Interest Group P.O. Box 1105 San Carlos, CA 94070 HISTORICAL PERSPECTIVE FORTH was created by Mr. Charles H. Moore in 1969 at the National Radio Astronomy C)Dservatory. Charlottesville. VA. It was created out of ctissatisfaction with available programming tools, especially for obser- vatory automation. Mr. Moore and several associates formed FORTH, Inc. in 1973 for the purpose of licensing and support of the FORTH Operating System and programming Lan- guage, and to supply application programming :o meet customers' unique requirements. The Forth Interest Group is centered in Northern California. although our membership of 2,400 is world- wide. It was formed in 1978 by FORTH programmers to encourage use of the language by the interchange of ideas through seminars and publications. EDITOR'S COLUMN Alan Taylor. in his speech at the FORTH Convention banquet, pointed out that FORTH is an incredibly powerful tool, snd not precisely a language. in the traditiowl sci~sc FORTH Wkvha close 10 the "naked machine and yet is as general a:id powerful as many High Level Lan- guages This makes FORTH the perfect langiiage for writing compilers or pseudo compilers for other !anyuages If we welt? to produce a compiler lor ANSI Standard COBOL. for InLtance. COBOL would run on any machine which had FOHTH running-which is easy' A major software house is presently writing an Ada compiler, and expects to have it out in 1983. I an1 uiliirig to Set that a working FORTH compiler for Ada could be written in half that time-does anyone want to take me UD 311 the bet7 S. B Bassett PUBLISHER'S COLUMN 1981) retropective FORTH DIMENSIONS has covpleted a whole year with the new format and a number of people think it gets better with each issue FORTH Interest Group has grown from 647 members on July 1st to over 2,400 thanks to Byte, EE Tlrnes, InfoWorlU. Cornpri'erWorld arid other publications The FORML Conference and FIG Convention were great succtsses Many new chapters are being formed, how about you forming one? FORTH vendors are increasing ainiost as fast as the membership FORTH is being im- plemented or' more and more machines and applica- tions are beginning !o roll out Its been a great year for us and we hope for you 1381 perspective FORTH DIMENSIONS will get better. we will have paid guest editors for each issue A number of new publications and other FIG items w~ll be introduced !see order form) A number of mailings will be done to FIG members about products available (if you don't want to receive these mailings, please drop us a note) We'll be doing more publicity to trade maga- zines and at complrter shows We need more aticles for FORTH DIMENSIONS, send yours in Happy New Year1 Roy Martens Page 120 FORTH DIMENSIONS II/5
A NEW SYNTAX FOR DEFINING DEFINING WORDS William F. Ragsdale ABSTRACT The computer language FORTH util- izes a syntax that is generally con- text free (i.e., postfix, or reverse Polish). However, deviations from this principle are noted in the syntax for words that themselves define words. This paper presents an altered form, which improves clarity of expression, and generalizes the con- struction for compilers which generate FORTH systems (meta-FORTH). BACKGROUND Compilation of FORTH programs con- sists of adding to memory a sequence of numerical values (addresses) corre- sponding to source text (words). This period is called compile-time. These values, called compilation addresses, are later interpreted by the address interpreter (at their run-time). They specify actual machine code which is ultimately executed, under control of the address interpreter. 1. FORTH source syntax is close to FORTH object code. 2. Traditional computer languages require significant processing to convert their syntax to object code. The syntax con- version is specified using Backus-Naur statements or "rail-road-track" diagrams of N. Wirth. 3. The traditional compiler's con- version adds complexity to the compiler, increases complexity and compiler size. It also masks the results from the user FORTH DIMENSIONS II/5 so that the use can't see or control the object code FORTH reduces complexity by requiring the user to write in a direct, simple syntax. The espoused benefits are: 1. The programmer directly con- trols program flow. Inef f i- ciency should be more apparent to the programmer. 2. The compiler is simpler, smaller, and more time efficient. 3. Compiler functions may be added by the programmer consistent with those previously in the system. The arguments against having to write in this form include: 1. God created infix notation. If not so, why did we learn it as children? God doesn't lie to little children. 2. Languages are created by compiler writers, not compiler users. Therefore, let these brilliant sources have a larger part of the pie (read headaches for pie). For completeness, it should be noted that program branching requires reference to addresses not at the point of compilation. The compiling words of FORTH (DO, UNTIL, IF, etc.) use the compile time stack to hold interim addresses which specify such branching. The nesting of condition- als keeps this process simple and efficient, and obiviates the need for backtracking or looking ahead in the source text. Page 121
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5 - Forth Interest Group

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