On Friday 16 January 2009 9:42:46 am eyal.lotem@gmail.com wrote:
I think currently many modules are designed to be imported unqualified, and this is unfortunate. Haskell' libraries can fix this. For example, the various Monadic counterparts such as mapM, replicateM, etc could do without the "M" in their names, and one could use:
import qualified Control.Monad as M
M.for M.map
I don't think I can fully agree with this. The fooM functions are so named because their type is different in a fairly predictable way from ordinary foo functions. And there are, in fact, two different functions that could lay claim to M.map. One is named mapM, of course, but the other is liftM: liftM :: Monad m => (a -> b) -> m a -> m b Which is an implementation of the ordinary map using the methods of Monad. Similarly, Data.Traversable has two functions: mapM :: Monad m => (a -> m b) -> t a -> m (t b) fmapDefault :: Traversable t => (a -> b) -> t a -> t b So, do we end up with T.map is a monadic map, but T.mapDefault is an ordinary Functor map using the Traversable methods. There are also mapAccumL and mapAccumR, but those don't allow monadic functions like T.map, just pure functions like T.mapDefault (although, secretly it's T.map specialized to the state monad). Anyhow, if you have some easy way to view the types of these functions, that clears up their use quite a bit. However, the naming scheme is not purely due to "this is map from the Monad module we're going to import unqualified." There is some method to it. -- Dan