At 2003-01-06 03:14, Ross Paterson wrote:
class PreArrow ar where arr :: (a -> b) -> ar a b (>>>) :: ar a b -> ar b c -> ar a c ... class (PreArrow ar, Monoidal p u) => GenArrow ar p u where first :: ar a b -> ar (p a c) (p b c)
My own preference is something like this: class (PreArrow ar) => GenArrow' ar where arrApply :: ar p (q -> r) -> ar p q -> ar p r My GenArrow' is actually equivalent to Hughes' Arrow and I assume your GenArrow. In an ideal world, I could leverage my FunctorApply class to have something like this: class (Functor f) => FunctorApply f where -- first arg (fab) "executed" first fApply :: f (a -> b) -> (f a -> f b) -- first arg (fa) "executed" first fPassTo :: f a -> f (a -> b) -> f b fPassTo fa fab = fApply (fmap (\a ab -> ab a) fa) fab class (PreArrow ar,forall p. FunctorApply (ar p)) => GenArrow'' ar Unfortunately, GHC does not yet allow this kind of superclassing. <http://cvs.sourceforge.net/cgi-bin/viewcvs.cgi/*checkout*/hbase/Source/HBa se/Category/Functor.hs?rev=HEAD&content-type=text/plain> <http://cvs.sourceforge.net/cgi-bin/viewcvs.cgi/*checkout*/hbase/Source/HBa se/Category/Arrow.hs?rev=HEAD&content-type=text/plain> -- Ashley Yakeley, Seattle WA