On 2/18/11 6:36 PM, Isaac Dupree wrote:
On 02/18/11 18:21, Edward Kmett wrote:
Hrmm, the strict version will violate the laws for Functor:
(fmap (const 12) . fmap error) /= fmap (const 12 . error)
That's an issue, though. It means you can't use a Map that tries to keep its values always strict if you want to use class Functor with it. *Even if* it's a separate type in Data.SomeMap.Strict. (Unless you're willing to break the law in the presence of _|_ values.)
FWIW, it's still a (category theoretic) functor: (fmap (const 12) . fmap error) == fmap (const 12 .! error) where (f .! g) x = f $! g x ...it's just not an endofunctor. But the Functor class is for encoding endofunctors, so this detail doesn't help us much. At least, not directly. -- Live well, ~wren