Given this code in module X,
> type RM s a = s -> a
> instance Functor ((->) s) where
> map f m = \s -> f (m s)
> instance Monad ((->) s) where
> return a = \s -> a
> m >>= k = \s -> k (m s) s
> getStateRM f = \s -> s
which is imported in module Y, and used eg
> foo = getStateRM >>= \x -> return (x + x) :: RM Int Int
THEN ghc (versions 2.10, 3.02, 4.01) complain
No instance for `Monad (-> Int)'
arising from use of `return' at <FILE & LINE>
But the problem is cured by adding this line in the module which won't
compile
> {-#SPECIALISE instance Monad ((->) Int) #-}
So, is there a bug with calculation of instances?
(Hugs is quite happy with such constructions.)
Thanks,
Paul Callaghan
Durham
