Generating Specialized Interpreters for Modular Structural Operational Semantics

Modular Structural Operational Semantics (MSOS) is a variant of Structural Operational Semantics (SOS). It allows language constructs to be specified independently, such that no reformulation of existing rules in an MSOS specification is required when a language is extended with new constructs and features. Introducing the Prolog MSOS tool, we first recall how to synthesize executable interpreters from small-step MSOS specifications by compiling MSOS rules to Prolog clauses. Implementing the transitive closure of compiled clauses gives an executable interpreter in Prolog. Such interpreters, however, traverse each intermediate program term, resulting in a significant overhead in each step. We then show how to transform small-step MSOS specifications into corresponding big-step specifications via a two-step specialization by internalizing and extending the rules implementing the transitive closure in MSOS. Specialized specifications result in generated interpreters with significantly reduced interpretive overhead.