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arXiv · 1911.12737

LL(1) Parsing with Derivatives and Zippers

Romain Edelmann·Jad Hamza·Viktor Kunčak
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Abstract

In this paper, we present an efficient, functional, and formally verified parsing algorithm for LL(1) context-free expressions based on the concept of derivatives of formal languages. Parsing with derivatives is an elegant parsing technique, which, in the general case, suffers from cubic worst-case time complexity and slow performance in practice. We specialise the parsing with derivatives algorithm to LL(1) context-free expressions, where alternatives can be chosen given a single token of lookahead. We formalise the notion of LL(1) expressions and show how to efficiently check the LL(1) property. Next, we present a novel linear-time parsing with derivatives algorithm for LL(1) expressions operating on a zipper-inspired data structure. We prove the algorithm correct in Coq and present an implementation as a parser combinators framework in Scala, with enumeration and pretty printing capabilities.

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Romain Edelmann, Jad Hamza, Viktor Kunčak. 2019-11-28. LL(1) Parsing with Derivatives and Zippers. https://doi.org/10.1145/3385412.3385992

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