[Haskell] PROPOSAL: class aliases

[Wolfgang Jeltsch]

Am Donnerstag, 13. Oktober 2005 15:43 schrieb Simon Peyton-Jones:
> John
>
> Replying just to you to avoid spamming everyone.

Hmm, you did write to the list as well...

> [...]

> I don't agree.  What do you mean by "distinct types"?  In H98 both of
> these are ok:
>
> 	f :: CD a => ty
> 	f = ...code...
>
> 	g :: (C a, D a) => ty
> 	g = f

This is not okay.  Hugs gives this error message (with ty = a):

	Cannot justify constraints in explicitly typed binding
	*** Expression    : g
	*** Type          : (C a, D a) => a
	*** Given context : (C a, D a)
	*** Constraints   : CD a

> [...]

Best wishes,
Wolfgang