AN INTERPRETER FOR SNOBOL4- USING SOFTWARE SIMULATION APPROACH

Abstract

SNOBOL4 is the most widely used string processing language developed at Bell-telephone laboratories during 1960's. Its major application is to problems in which substantial amounts of character-string data must be processed in complex ways, e.g., in processing natural language text. In this dissertation, an interpretor for SNOBOL4 subset, whose syntax is given in Appendix-II, is implemented with AI 0L-60 as an host language. The complete implementation of the language is done in two phases. In the first phase, the source language written in SNOBOL4 is translated into an in termediate code. This intermediate code bears no resemblance to the hardware machine language. The translation of the source program to the intermediate code is done by the syntax analyser which calls basical analyzers routine whenever it needs t,)kens. The parsing technique used is operative pro. cadencefor expressions and recursive descent for the rest of the language. The intermediate form is simply a convenient input form for the software interpreter written in ALGOL-60, which acts as an abstract machine and executes the program. The major features of the language that are implemented are pattern-matching, assignment statements, pattern-matching with replm cement statement, input-output statement sequence control statements, and system defined functions which form the core of the SNOBOL4 language.