On Tue, Jun 26, 2007 at 10:00:02PM -0700, Iavor Diatchki wrote:
I can see how this function can be useful. However, I am strongly opposed to adding the general monadic version---not all monads support graceful failure, and for monads that do not support it, the only option is to throw a run-time exception, which is at odds with the purity of Haskell (which leads to headaches when you try to write robust code). I think that the "Maybe" version is perfectly adequate but if we have to have an overloaded version, then we should use "MonadPlus".
Also, no functions in Data.List work with Monads right now, so this one would be an exception. If dropPrefix is to use Monad interface, so should find, findIndex, lookup and elemIndex. $ echo ':b Data.List' | ghci | grep Monad $ echo ':b Data.List' | ghci | grep Maybe lookup :: (Eq a) => a -> [(a, b)] -> Maybe b elemIndex :: (Eq a) => a -> [a] -> Maybe Int find :: (a -> Bool) -> [a] -> Maybe a findIndex :: (a -> Bool) -> [a] -> Maybe Int unfoldr :: (b -> Maybe (a, b)) -> b -> [a] Best regards Tomek