On constructing efficient evaluators for attribute grammars

Abstract

An attribute grammar is an ordinary context-free grammar augmented with attributes and semantic rules for describing the semantics of terminal strings generated by the underlying context-free grammar. The meaning of a terminal string is revealed in two steps: first a parse tree is constructed for the string, and then a so-called evaluator defines the values of attribute instances attached to the parse tree. Many of these values are very temporary in nature, making it important to use the space allocated for them repeatedly. In this paper the evaluator construction method of Kennedy and Warren is improved in two ways. First, we present how temporary values can be detected and stored in a stack so that their space requirement is linear in the height of the parse tree. Second, we demonstrate how to reduce the size of the evaluator. In the best case a reduction by an exponential factor can be achieved.