Lets say I've got Interface IFoo<X,Y> Where X : IBar Where Y : IBar { } Would seem to translate roughly to.... class (IBar x, IBar y) => IFoo foo x y ? (or does it?) -----Original Message----- From: haskell-cafe-bounces@haskell.org [mailto:haskell-cafe-bounces@haskell.org] On Behalf Of Nicholls, Mark Sent: 28 December 2007 11:30 To: Chaddaï Fouché Cc: haskell-cafe@haskell.org Subject: RE: [Haskell-cafe] what does @ mean?..... Lovely....thank you very much....another small step forward. -----Original Message----- From: Chaddaï Fouché [mailto:chaddai.fouche@gmail.com] Sent: 28 December 2007 11:29 To: Nicholls, Mark Cc: Alfonso Acosta; haskell-cafe@haskell.org Subject: Re: [Haskell-cafe] what does @ mean?..... 2007/12/28, Nicholls, Mark <Nicholls.Mark@mtvne.com>:
So in the example given...
mulNat a b | a <= b = mulNat' a b b | otherwise = mulNat' b a a where mulNat' x@(S a) y orig | x == one = y | otherwise = mulNat' a (addNat orig y) orig
Is equivalent to
mulNat a b | a <= b = mulNat' a b b | otherwise = mulNat' b a a where mulNat' (S a) y orig | (S a) == one = y | otherwise = mulNat' a (addNat orig y) orig
?
Yes, but in the second version, it has to reconstruct (S a) before comparing it to "one" where in the first it could do the comparison directly. In this cas there may be some optimisation involved that negate this difference but in many case it can do a real performance difference. The "as-pattern" (@ means as) is both practical and performant in most cases. -- Jedaï _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe