castAny :: (Storable a, Storable b) => a -> b castAny = unsafePerformIO . genericCast where genericCast :: (Storable a, Storable b) => a -> IO b genericCast v = return undefined >>= \r -> allocaBytes (max (sizeOf v) (sizeOf r)) $ \p -> poke p v >> if False then return r else peek (castPtr p)
let a = -1000 :: Int16 castAny a :: Word16 --> 64536 castAny a :: Ptr () 0xb4c2fc18
Try it on a big endian architecture, or one that has alignment restrictions, or a different size for HsChar or so forth. Casting by 'punning' (as the C folks like to call it) does have uses, but they are generally hardware dependent and useful only in certain rare circumstances that a generic cast probably isn't likely to fill.
Do you think this could be used as a way to handle C unions? If I had something like union example { struct firstview { char c; int n; } fv; long double ld; }; and 'firstview' had been mapped in Haskell as, say, FirstView {firstViewC :: CChar, firstVewN :: CInt} I could check what I would get after pokeing values using: (firstViewN . unionCast) (pi :: CDouble) Note that I changed the name from castAny to unionCast to reflect its use. Thanks for your comments, Maurício