[Hat] How does the FFI work?

I'm having problems with the FFI and GHC 6.6. Namely, I edited one of the tools files (Detect.hs) that contains FFI imports, and now I end up with generalised death when I try to compile. The source compiles fine, but on linking I get: /usr/bin/ld: Undefined symbols: _anySuspect _extendParentSet _findMainUse _newParentSet _nextChild The C and H files are hanging around as they should be. Any ideas what's going on? Bob