Parsing Expression GLL

TL;DR

This paper introduces PEGLL, an extended GLL parsing algorithm that supports parsing expression grammars with ordered choice and lookahead, broadening the scope of parsers for complex grammar types.

Contribution

The authors extend the GLL algorithm to support parsing expression grammars, including ordered choice and lookahead, and adapt parser-generation tools accordingly.

Findings

Supports a broader class of grammars including PEGs and CFGs

Modified parser-generator to incorporate new operators and lexing strategies

Retains support for unordered choice while adding ordered choice capabilities

Abstract

This paper presents an extension of the GLL parsing algorithm for context-free grammars which also supports parsing expression grammars with ordered choice and lookahead. The new PEGLL algorithm retains support for unordered choice, and thus parses a common superset of context-free grammars and parsing expression grammars. As part of this work, the authors have modified an existing GLL parser-generator to support parsing expression grammars, adding operators for common parsing expressions and modifying the lexer algorithm to better support ordered choice.