Wed, 26 Jul 2000 15:46:16 +0100, Claus Reinke <[EMAIL PROTECTED]> pisze:
> class CallN sigF sig where
> callN :: IO sigF -> sig
AAA! Thank you, it works now!
Having IO in the argument here, together with doing the work inside
the argument of the recursive call, was The Lacking Idea.
------------------------------------------------------------------------
class ForeignArg f h where
convertArg :: (f -> IO a) -> h -> IO a
class ForeignRes f h where
convertRes :: IO f -> IO h
class Call f h where
callIO :: IO f -> h
instance ForeignRes fr hr => Call (IO fr) (IO hr) where
callIO f = f >>= convertRes
instance (ForeignArg fa ha, Call ff hf) => Call (fa -> ff) (ha -> hf) where
callIO f = callIO . convertArg (\fa -> f >>= return . ($fa))
call:: Call f h => f -> h
call = callIO . return
------------------------------------------------------------------------
Example of usage:
openFd:: String -> Int -> Int -> IO Fd
openFd = call openC
foreign import "open" unsafe openC :: CString -> CInt -> CMode -> IO (ThrowIfMinus1 Fd)
> PS. Even if this should do what you want, I'm not sure how
> much type-class machinery and partial applications you'll
> want to introduce at the ground level of a foreign function
> interface. Unless compilers are very good at getting all
> this machinery out of the way, the word overhead comes
> to mind.
I hope that compilers will be able to reasonably inline it, eliminating
the overhead. At least theorethically is should be possible.
Unfortunately I guess that GHC does not unfold any recursion.
Maybe it won't be hard to make it possible to add a hint:
{-# UNFOLD 6 callIO #-}
that the programmer politely asks to try to inline and unfold the
recursion up to 6 times at call sites to see if it finishes?
If tuples were changed to be defined recursively - I think it would
work, be compatible and be a good idea - then it would be useful to
have (==) on small tuples with class dispatching optimized away.
--
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