+1 in favour. This is Haskell, and as such, program crashable effects should not be the default, whenever possible. Regarding support for older programs relying on IO effects here, deprecated versions with the old type would be a good concession to backwards compatibility, or adding a lifter of, ... => Maybe a -> m a to Maybe might also be wise. -- Don ross:
Several functions on containers used to have types like
lookup :: (Ord k) => k -> Map k a -> Maybe a
but these were generalized to
lookup :: (Monad m, Ord k) => k -> Map k a -> m a
The only methods of Monad used are return and fail. The problem is that, depending on the monad, fail can be an ordinary value or a runtime error: this device makes it harder to check whether a program is safe, because it hides possible runtime errors among testable conditions.
The proposal is to change these signatures back, specializing them to Maybe.
The functions involved are:
lookup :: Ord k => k -> Map k a -> Maybe a lookupIndex :: Ord k => k -> Map k a -> Maybe Int minViewWithKey :: Map k a -> Maybe ((k,a), Map k a) maxViewWithKey :: Map k a -> Maybe ((k,a), Map k a) minView :: Map k a -> Maybe (a, Map k a) maxView :: Map k a -> Maybe (a, Map k a)
lookup :: Key -> IntMap a -> Maybe a maxViewWithKey :: IntMap a -> Maybe ((Key, a), IntMap a) minViewWithKey :: IntMap a -> Maybe ((Key, a), IntMap a) maxView :: IntMap a -> Maybe (a, IntMap a) minView :: IntMap a -> Maybe (a, IntMap a)
minView :: Set a -> Maybe (a, Set a) maxView :: Set a -> Maybe (a, Set a)
maxView :: IntSet -> Maybe (Int, IntSet) minView :: IntSet -> Maybe (Int, IntSet)
No information is lost, because in each case there is a single failure mode. _______________________________________________ Libraries mailing list Libraries@haskell.org http://www.haskell.org/mailman/listinfo/libraries