Semantic routines and LR(k) parsers

Summary Most applications of parsing require that the parser call semantic action routines while processing the input. For LR(k) parsers it is well known that a semantic action routine can be called when the end of a production is recognized. Often, however, it is desirable to call routines at other times.This paper presents fast algorithms that determine, for an LR(k) (or SLR(k)) grammar, which positions are suitable for calling routines. The algorithms are practical for use with LR(1) (SLR(1)) parser building programs, because the worst case running time is dominated by the time required to build the LR(1) (SLR(1)) parser. Applications of the algorithms to attribute grammars and automatic indentation are discussed.