A Mixed Approach for Building Extensible Parsers

For languages whose syntax is fixed, parsers are usually built with a static structure. The implementation of features like macro mechanisms or extensible languages requires the use of parsers that may be dynamically extended. In this work, we discuss a mixed approach for building efficient top-down dynamically extensible parsers. Our view is based on the fact that a large part of the parser code can be statically compiled and only the parts that are dynamic should be interpreted for a more efficient processing. We propose the generation of code for the base parser, in which hooks are included to allow efficient extension of the underlying grammar and activation of a grammar interpreter whenever it is necessary to use an extended syntax. As a proof of concept, we present a prototype implementation of a parser generator using Adaptable Parsing Expression Grammars (APEG) as the underlying method for syntax definition. We show that APEG has features which allow an efficient implementation using the proposed mixed approach.