8 Apr
2011
8 Apr
'11
11:55 p.m.
On 4/8/11 8:55 AM, Twan van Laarhoven wrote:
-- this class is useful beyond this FRP library, -- you might already be able to find it on hackage somewhere class Functor f => Filterable f where filter :: (a -> Bool) -> f a -> f a -- filter p . fmap f == fmap f . filter (p . f) -- filter (const True) == id -- filter p . filter q == filter (\x -> p x && q x)
There are a few other methods that should be added to this typeclass. In particular, filterMap :: (a -> Maybe b) -> f a -> f b which fuses the first rule and saves the redundant passes and evaluations. In a similar vein you may want a class for versions that allow applicative/monadic functions along with the sequenceA/sequence capabilities of Traversable. -- Live well, ~wren