A more generic version of mapM

\begin{code}
module MapG where
import Array
import Event 
class Monad d => MapG c a b d where
 mapG :: (a -> d b) -> c a -> d (c b)

instance Monad d => MapG [] a b d where
 mapG = mapM

instance (Ix a,Monad d) => MapG (Array a) b c d where
 mapG = mapGArray 

instance Monad d => MapG Maybe a b d where
 mapG f Nothing = return Nothing
 mapG f (Just a) = f a >>= return . Just 

mapGArray :: (Monad d,Ix c) => (a -> d b) -> Array c a -> d (Array c b)
mapGArray f arr = 
 do
  vals <- mapM (\n -> do v <- f $ arr ! n
                         return (n,v)) 
               (range $ bounds arr)
  return $ array (bounds arr) vals
 
instance MapG Event a b IO where
 mapG f e = return $! withIOE e f
\end{code}