GHC ignores Objective C sources unless -x c is passed to it on the command line before the source files.
As far as I could tell there is no way to pass that option to GHC through Cabal so no .m files ever get built (well.. not completely true - setting ghc-options works but that breaks compilation of Haskell code).
One way to get this to work would be to just add some extra code in Cabal to automatically pass -x c for .m files. This is probably a bad idea as someone might want or need to compile files using some other extension at some point.
Another option is add some way of specifying compile options on a per-file (or group of files) basis: setting ghc-options to -x c just for one set of files. Still very limited but it's an improvement over the first option.
Third option I can think of is to add a way of specifying compiler/extension pairs in Cabal so given compilers are automatically used to compile files with corresponding extensions.
Depending on how much time I have I might look into adding this functionality myself but would like some feedback on which approach to take.
Otherwise I might have to stick with autotools and ignore Cabal until it gets a bit more mature and flexible.
