Bracketed two-level grammars — a decidable and practical approach to language definitions

Abstract

Bracketed two-level grammars are not a variation of two-level grammars (van Wijngaarden grammars) but consitute a restriction within the general scheme. The resulting grammars give rise to an effective top-down analysis, where the replacement of metanotions is governed by rules similar to the evaluation dependencies in attribute grammars. Supplemented by the formalized concept of predicates, the class of languages is shown to be decidable and includes EXSPACE. Moreover it has been demonstrated by a description of PASCAL-S, that the grammars are versatile enough to yield quite readable formal definitions of programming languages. To allow a critical comparison, a grammar for the syntax of ASPLE is given in an Appendix.