Packrat Parsers Can Handle Practical Grammars in Mostly Constant Space

摘要

Packrat parsing is a powerful parsing algorithm presented by Ford in 2002. Packrat parsers can handle complicated grammars and recursive structures in lexical elements more easily than the traditional LL(k) or LR(1) parsing algorithms. However, packrat parsers require O(n) space for memoization, where n is the length of the input. This space inefficiency makes packrat parsers impractical in some applications. In our earlier work, we had proposed a packrat parser generator that accepts grammars extended with cut operators, which enable the generated parsers to reduce the amount of storage required.rnExperiments showed that parsers generated from cut-inserted grammars can parse Java programs and subset XML files in bounded space.rnIn this study, we propose methods to automatically insert cut operators into some practical grammars without changing the accepted languages. Our experimental evaluations indicated that using our methods, packrat parsers can handle some practical grammars including the Java grammar in mostly constant space without requiring any extra annotations.