Sure, depending on the size and structure of the grammar you might want to split it into multiple classes. Yes, that's a possibility that works well. Maybe better use the accessor #productionAt: to access the cached productions of a different grammar, otherwise you end up with much larger grammars than necessary. The problem of splitting up the grammars as you propose is that it is not that easy anymore (but still possible) when you want to use subclassing to customize the grammar with different production actions. Another (and more traditional approach) is to use a separate lexer: You can see that in TextLint (check on squeaksource.com). There we have different lexers for plain text, LaTeX and HTML; and a parser for a 'natural language' of words, sentences, and paragraphs (very simple) that can be composed in different ways. For Java such a split probably doesn't make sense, but it is a good example of PetitParser being very flexible to different requirements. Also you might want to look at my work on language embedding, especially <http://scg.unibe.ch/archive/papers/Reng09cLanguageBoxes.pdf>. There we programmatically compose different languages modeled as PPCompositeParser instances at specific join-points. Lukas -- Lukas Renggli www.lukas-renggli.ch