Parsing Reflective Grammars

TL;DR

This paper introduces reflective grammars that can modify their syntax during parsing, enabling more flexible language extension, and presents a correct, efficient parsing algorithm based on Earley's algorithm.

Contribution

It proposes a novel reflective grammar framework and an Earley-based parsing algorithm that supports dynamic syntax modifications during parsing.

Findings

The algorithm correctly parses reflective grammars.

Performance is asymptotically comparable to Earley's algorithm.

Reflective grammars enable more powerful syntax extension systems.

Abstract

Existing technology can parse arbitrary context-free grammars, but only a single, static grammar per input. In order to support more powerful syntax-extension systems, we propose reflective grammars, which can modify their own syntax during parsing. We demonstrate and prove the correctness of an algorithm for parsing reflective grammars. The algorithm is based on Earley's algorithm, and we prove that it performs asymptotically no worse than Earley's algorithm on ordinary context-free grammars.