On Sat, Sep 30, 2006 at 12:41:42PM +0100, Conor McBride wrote:
So, with this arrangement, quite a lot of library functionality is potentially affected (good!), especially if Traversable is also kicking around, allowing us
crush :: (Monoid t, Traversable f) => (s -> t) -> f s -> t
(1) Which library functions should just be binned? (2) Which library functions should be retained but generalised (eg, working for Applicative rather than Monad, or any Traversable f rather than just [])? In particular, what happens to mapM?
For some possible answers, see http://www.haskell.org/ghc/dist/current/docs/libraries/base/Data-Foldable.ht... http://www.haskell.org/ghc/dist/current/docs/libraries/base/Data-Traversable... coming soon to all Haskell implementations. For crush, there's foldMap :: (Foldable f, Monoid m) => (a -> m) -> f a -> m Ashley's quite ambitious to push this refactoring of Monad for Haskell', since there is limited experience with Applicative, and class system changes that might help with fine-grained hierarchies are unlikely to be available, but I wish him luck. I've collected several such issues on the StandardClasses page.