We describe how multimodal grammars for dialogue systems can be
written using the Grammatical Framework (GF) formalism. A
proof-of-concept dialogue system constructed using these techniques is
also presented. The software engineering problem of keeping grammars
for different languages, modalities and systems (such as speech
recognizers and parsers) in sync is reduced by the formal relationship
between the abstract and concrete syntaxes, and by generating
equivalent grammars from GF grammars.