If we look at swap from the standpoint of the laws/RULES it should support, viewing Hask over (,) as a symmetric monoidal category you get something like:

{-# RULES
"swap . swap = id" forall x. swap (swap x) = x
"fst . swap = snd" forall x. fst (swap x) = snd x
"snd . swap = fst" forall x. snd (swap x) = fst x
 #-}

That seems to argue for the lazy definition being the default to avoid the strict pattern match in swap breaking the latter very pleasing equalities.

-Edward Kmett

On Wed, Jun 17, 2009 at 8:52 PM, <roconnor@theorem.ca> wrote:
How about this: swap should be lazy because that is how H98 defines uncurry:

uncurry          :: (a -> b -> c) -> ((a, b) -> c)
uncurry f p      =  f (fst p) (snd p)


--
Russell O'Connor                                      <http://r6.ca/>
``All talk about `theft,''' the general counsel of the American Graphophone
Company wrote, ``is the merest claptrap, for there exists no property in
ideas musical, literary or artistic, except as defined by statute.''
_______________________________________________
Libraries mailing list
Libraries@haskell.org
http://www.haskell.org/mailman/listinfo/libraries