Tom Schrijvers wrote:
> On Wed, 26 Mar 2008, Ganesh Sittampalam wrote:
>> On Wed, 26 Mar 2008, Ross Paterson wrote:
>>
>>> On Wed, Mar 26, 2008 at 08:52:43PM +0000, Ganesh Sittampalam wrote:
>>>> I'm a bit confused about why the following program doesn't compile
>>>> (in any of 6.6.1, 6.8.1 and 6.9.20080316). Shouldn't the Ord (a, b)
>>>> context be reduced?
>>>
>>> To use bar, you need (Ord a, Ord b). You're assuming that Ord (a, b)
>>> implies that, but it's the other way round.
> Logically, the implication holds. There's an equivalence:
>
> Ord a /\ Ord b <=> Ord (a,b)
Unfortunately, GHC accepts the following:
{-# LANGUAGE FlexibleInstances #-}
module Foo2 where
data Foo = Foo
deriving Eq
instance Ord (Foo, Foo) where
(Foo, Foo) < (Foo, Foo) = False
Cheers,
Ganesh
==============================================================================
Please access the attached hyperlink for an important electronic communications
disclaimer:
http://www.credit-suisse.com/legal/en/disclaimer_email_ib.html
==============================================================================
_______________________________________________
Glasgow-haskell-users mailing list
Glasgow-haskell-users@haskell.org
http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
