[Haskell-beginners] (no subject)
dennis.raddle at gmail.com
Mon Sep 3 05:32:13 CEST 2012
I wanted to run the map function from Data.Map, let's call it M.map, but
inside a monad transformer stack including the Error monad.
M.map has this type:
M.map :: (Ord k) => (a -> b) -> Map k a -> Map k b
However, I want to use a mapping function that has type
(Monad m) => a -> m b
(i.e. errors could be thrown during the computation, a log could be
I wrote the following. Any comments on this way of doing things?
mapMapM :: (Monad m, Ord k) => (a -> m b) -> Map k a -> m (Map k b)
mapMapM g mapIn = do
let h (k,a) = do
b <- g a
y <- mapM h (M.toAscList mapIn)
return $ M.fromAscList y
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