I may be totally wrong, but I read in Hughes paper than in Stream Processors, Either is "more a product" than (,) . It could be interesting to parameter the arrow by product, in order than the multiplexing is done using this product when using the new notation for arrow. Best regards, Nicolas Oury On Mon, 6 Jan 2003, Ashley Yakeley wrote:
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