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Chapter 1 : INTRODUCTION

The reference section describes the SNOBOL4 system. It will tell you how to create and run SNOBOL4 programs, and catalogs all the standard language features. The tutorial section can be consulted for illustrative uses of various functions and operators.

SNOBOL4 is a full implementation of the powerful development language SNOBOL4 for the IBM PC and the entire 8086/286/386 family of computers. It has all the features of mainframe SNOBOL4, plus numerous useful extensions. Compatibility with mainframe SNOBOL4 is achieved by basing this product on the Macro Implementation used on such mainframes as the IBM 370 and the CDC 7600. Thus, it incorporates a thoroughly tested implementation in its entirety. All SNOBOL4 string and pattern matching facilities available in the mainframe environment are now available to the personal computer user.

The SNOBOL4 program contains both a compiler and interpreter. They are inseparable, and share many common routines. Your source program is compiled into a compact internal notation, which is interpreted during execution. More information on the internal code may be found in Griswold's "The Macro Implementation of SNOBOL4;" see file SNOBOL4.DOC for ordering information.

1.1 LANGUAGE BACKGROUND

In 1962, several researchers at Bell Telephone Laboratories (BTL) were applying computers to problems such as factoring multivariate polynomials and symbolic integration. Available tools were the Symbolic Communication Language (SCL), an internal BTL product for processing symbolic expressions, and COMIT, designed for natural-language analysis. Both proved inadequate, and frustration with them led the researchers to attempt the design of a new language.

The original SNOBOL was developed by David J. Farber, Ralph E. Griswold, and Ivan P. Polonsky, and was first implemented on an IBM 7090 computer in 1963. The name, SNOBOL, came after the implementation, and ostensibly stands for StriNg Oriented symBOlic Language.

It was soon discovered that SNOBOL was applicable to a much wider range of problems. In fact, the language proved more interesting than the problems it was intended to solve. As more people used it, new features such as recursive functions were added, and its generality grew. By 1964, it had become SNOBOL3, and was available on such machines as the IBM 7094, CDC 3600, SDS 930, Burroughs 5500, and the RCA 601. Because these implementations were all written from scratch, each machine introduced its own dialect of the language.

SNOBOL3 had only one data type, the string. The desire for additional data types, more complex pattern matching, and other features led to a major redesign of the language in 1966, by Ralph Griswold, Jim Poage, and Ivan Polonsky. The new language -- SNOBOL4 -- was also designed to be portable to other machines. Most of SNOBOL4 was completed by 1967, although some features, such as operator redefinition, did not appear until 1969. Portability was achieved by writing the system in a macro assembly language for an abstract machine, hence the name "Macro Implementation of SNOBOL4." By 1970 it was available on nine different types of mainframes. Currently, it is available on most large- and medium-scale computers.

The SNOBOL4 language evolved on computers whose primary input/output devices were the card reader, card punch, and line printer. The current breed of microcomputers are interactive, rather than batch-oriented. Thus, SNOBOL4 contains slight alterations of the language to conform to the personal computer environment. For example, the preassigned output keyword PUNCH has been replaced by SCREEN. Experienced SNOBOL4 programmers will find little incompatibility with familiar implementations. Most existing SNOBOL4 programs should operate correctly using SNOBOL4 with little or no change.

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