"no input files"

buzzard(150)% cat Two-part.hs
main = return ()
buzzard(151)% ghc --make Two-part.hs
ghc-5.04.2: chasing modules from: Two-part.hs
Compiling Main             ( Two-part.hs, ./Two-part.o )
ghc: linking ...
buzzard(152)% ghc --make Two-part
ghc-5.04.2: no input files
Usage: For basic information, try the `--help' option.

GHC usually has no problem when I leave off the ".hs" extension.  Why
should it matter that there's a '-' in the file name?