>>> HashSet.map show (HashSet.fromList [1,2,3]) HashSet.fromList ["1","2","3"]
map f [x1, x2, ..., xn] == [f x1, f x2, ..., f xn] map f [x1, x2, ...] == [f x1, f x2, ...]
>>> map (+1) [1, 2, 3] [2,3,4]
runAccum (mapAccum f m) = f . runAccum m
runAccumT (mapAccumT f m) = f . runAccumT m
runCont (mapCont f m) = f . runCont m
runContT (mapContT f m) = f . runContT m
runExcept (mapExcept f m) = f (runExcept m)
runExceptT (mapExceptT f m) = f (runExceptT m)
runMaybeT (mapMaybeT f m) = f (runMaybeT m)
runRWS (mapRWS f m) r s = f (runRWS m r s)