An Introduction to S/SL: Syntax/Semantic Language

Abstract

S/SL (Syntax/Semantic Language) is a language that was developed for implementing compilers.A subset called SL (Syntax Language) has the same recognition power as do LR(k) parsers.Complete S/SL includes invocation of semantic operations implemented in another language such as PASCAL.S/SL implies a top-down programming methodology.First, a data-free algorithm is developed in S/SL.The algorithm invokes operations on "semantic mechanisms."A semantic mechanism is an abstract object, specified, from the point of view of the S/SL, only by the effect of operations upon the object.Later, the mechanisms are implemented apart from the S/SL program.The separation of the algorithm from the data and the division of data into mechanisms reduce the effort needed to understand and maintain the resulting software.S/SL has been used to construct compilers for SPECKLE (a PL/I subset), PT (a PASCAL subset), Toronto EUCLID, and Concurrent EUCLID.It has been used to implement scanners, parsers, semantic analyzers, and code generators.S/SL programs are implemented by translating them into tables of integers.A "table walker" program executes the S/SL program by interpreting this table.The translation of S/SL programs into tables is performed by a program called the S/SL processor.This processor serves a function analogous to that served by an LR(k) parser generator.The implementation of S/SL is simple and portable.It is available in a small subset of PASCAL that can easily be transliterated into other high-level languages.