Island Grammar-Based Parsing Using GLL and Tom

Ali Afroozeh, Jean-Christophe Bach, Mark van den Brand, Adrian Johnstone, Maarten Manders, Pierre-Etienne Moreau, Elizabeth Scott

Research output: Chapter in Book/Report/Conference proceedingConference contribution


Extending a language by embedding within it another language presents significant parsing challenges, especially if the embedding is recursive. The composite grammar is likely to be nondeterministic as a result of tokens that are valid in both the host and the embedded language. In this paper we examine the challenges of embedding the Tom language into a variety of general-purpose high level languages. Tom provides syntax and semantics for advanced pattern matching and tree rewriting facilities. Embedded Tom constructs are translated into the host language by a preprocessor, the output of which is a composite program written purely in the host language. Tom implementations exist for Java, C, C#, Python and Caml. The current parser is complex and difficult to maintain. In this paper, we describe how Tom can be parsed using island grammars implemented with the Generalised LL (GLL) parsing algorithm. The grammar is, as might be expected, ambiguous. Extracting the correct derivation relies on our disambiguation strategy which is based on pattern matching within the parse forest. We describe different classes of ambiguity and propose patterns for resolving them.
Original languageEnglish
Title of host publicationSoftware Language Engineering Lecture Notes in Computer Science
Subtitle of host publication5th International Conference, SLE 2012, Dresden, Germany, September 26-28, 2012, Revised Selected Papers
Number of pages20
ISBN (Electronic)978-3-642-36089-3
Publication statusPublished - 2013

Cite this