To hopefully wind up this discussion, I'd like to make three proposals: 1. That if a compiler understands an in-file pragma specifying options, it should take the form {-# OPTIONS_<compiler> ... #-}. 2. We introduce a new pragma to specify the language extensions in force for the current source file. I suggest: {-# LANGUAGE <ext1>,...,<extn> #-} where <ext> is taken from the list of extensions understood by Cabal in the 'extensions' field of a package description (eg. OverlappingInstances, RecursiveDo, etc.). 3. We add CPP to the list of extensions in Cabal, so you can say {-# LANGUAGE CPP #-} to get C preprocessing in the current file, or add CPP to the list of extensions in the package description to get CPP on every file. That doesn't preclude also using a .cpp extension, but it means you don't have to. Hmm, I've just realised some problems with this. Hugs probably won't be implementing {-# LANGUAGE #-} any time soon (I imagine?) so it wouldn't be portable. Also old compilers don't implement it, so we have a difficult migration path. Perhaps for the time being we just do 1 & 3, and use the package-wide list of extensions for portability. Cheers, Simon