[jhc] some FFI questions

[Samuel Bronson]

First of all, I'm wondering what the intended uses of the lookupCType
and lookupCType' functions are. It seems like lookupCType tells you
the type that should be used in marshalling a type, and lookupCType
tells you the primitive type that is used in the representation of a
type as well as how to extract the value from it. I'm not sure how to
go from there to actually converting to/from the correct primitive
type to use in interfacing with C code...

Another question is: what sort of E type should an imperative foreign
export use? Consider:

foreign export hello :: Int -> IO ()
hello n = putStrLn ("Hello, "++show n)

foreign export foo :: IO Int
foo :: Num a => IO a
foo = return 1

Should they just use IO? I guess that's what main does...