Parsing with Earley Virtual Machines

Earley parser is a well-known parsing method used to analyse context-free grammars. While being less efficient in practical contexts than other generalized context-free parsing algorithms, such as GLR, it is also more general. As such it can be used as a foundation to build more complex parsing algorithms. We present a new, virtual machine based approach to parsing, heavily based on the original Earley parser. We present several variations of the Earley Virtual Machine, each with increasing feature set. The final iteration of the Earley Virtual Machine is capable of parsing context-free grammars with data-dependant constraints and support grammars with regular right hand sides and regular lookahead. We show how to translate grammars into virtual machine instruction sequences that are then used by the parsing algorithm. Additionally, we present two methods for constructing shared packed parse forests based on the parse input.