Abstract
Recently, a new way to represent context-free grammars (CFG) has been put forward. The representation uses a directed graph called the Grammar Flow Graph (GFG). The GFG provides a framework to parse all context-free languages (CFL) based on Earley's algorithm that is easier to understand than the original Earley's presentation. In addition, the GFG connects two seemingly distant concepts for regular language parsing and parsing of CFLs. It shows that simulating all the moves through a non-deterministic finite-state automaton (NFA) can be generalized to moving along all appropriate GFG paths. This paper introduces a GFG parser generator whose functionalities are equivalent to popular parser generators like Yacc or Bison. However, it works on all CFGs-ambiguous or unambiguous. Our parser generator takes a grammar file that represents strings in CFL as an input and outputs a parser program to parse those strings. We evaluate it against two other parser generators, one based on the original Earley's representation and the other based on the Cocke-Younger-Kasami (CYK) algorithm. The result indicates that the performance of our parser generator is on a par with that based on the original Earley's scheme and superior to the CYK's parser generator. The code for our parser generator can be downloaded from the following link: https://bitbucket.org/kramatk/earleyparser.
Published Version
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