Multiple modules in a file

Hi, I don't seem to be able have multiple modules in one file (at least for hugs and ghc). The gentle intro says that there is no restriction and I can't find any mention in the ghc jobs (apart from a recommendation to name a file after the module it contains to help make). It's not a desperate problem - I can split files - but I'd like to know if I'm doing something stupid, or if this is a real restriction. (I can see arguments why from an engineering/maintenance point of view, but one module is small and fits nicely with another; it also makes literate programming slightly more complicated). Thanks, Andrew -- http://www.andrewcooke.free-online.co.uk/index.html