map :: Functor [] => (a -> b) -> [a] -> [b] already has existing, different, semantics today to what Greg is proposing here. It is asking for an instance of Functor for [] to be supplied. Since that instance exists an is scope, the constraint is trivially satisfied, so this collapses to map :: (a -> b) -> [a] -> [b] the signature we already have, with the semantics we already have. -Edward On Tue, Feb 17, 2015 at 3:38 AM, Henning Thielemann < lemming@henning-thielemann.de> wrote:
On Mon, 16 Feb 2015, Greg Weber wrote:
I had an idea whose goal is to ease people into Foldable, Traversable,
etc. There could be a notation that shows the generalization that is occurring.
map :: Functor [_] => (a -> b) -> [a] -> [b]
This means that the syntax for the list type is now syntax for the variable created by the Functor constraint.
Btw. there is already a prefix name for the list type constructor, namely '[]'. Thus I think your example would be:
map :: Functor [] => (a -> b) -> [a] -> [b]
_______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries