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 ==============================================================================