Peter Simons wrote:
Note my original definition:
type Buffer = (Ptr Word8, Int)
data StreamProc ctx a = SP { start :: IO ctx , feed :: ctx -> Buffer -> IO ctx , commit :: ctx -> IO a }
So you would use it like this:
foo :: StreamProc ctx a -> IO a foo sp = do ctx <- start sp (ptr,n) <- "read buffer" ctx' <- feed sp ctx (ptr,n) ... commit sp ctx'
Sorry, my mistake. I was thinking of StreamProc as a type class. What I meant was this: bar :: StreamProc ctx a -> IO (a,a) bar sp = do ctx <- start sp (ptr1,n1) <- ... (ptr2,n2) <- ... ctx1 <- feed sp ctx (ptr1,n1) ctx2 <- feed sp ctx (ptr2,n2) val1 <- commit sp ctx1 val2 <- commit sp ctx2 return (val1,val2) My point is just that bar typechecks and therefore must do something at runtime; what does it do? This is a genuine question -- I'm hoping the answer will help me understand what you're trying to do here. -- Ben