On Monday 22 April 2002 23:31, Hal Daume III wrote:
> I'd like to be able to define something like
>
> instance Eq a => Coll (-> Bool) a where
> empty = \_ -> False
> single x = \y -> if x == y then True else False
> union a b = \x -> a x || b x
> insert s x = \y -> x == y || s y
>
> and the like
>
> However, this seems to be impossible. Is this the type lambda restriction
> that's been discussed recently on the mailing list?
>
> - Hal
Hi Hal,
I'd do it like this, hope it helps.
----------------------------------
module Test where
newtype BinClass a = BC (a->Bool)
class Coll c a where
empty :: c a
single :: a->c a
union :: c a->c a->c a
insert :: c a->a->c a
instance Eq a => Coll BinClass a where
empty = BC(\_->True)
single x = BC(\y -> if x == y then True else False)
union (BC a) (BC b) = BC(\x -> a x || b x)
insert (BC s) x = BC(\y -> x == y || s y)
_______________________________________________
Haskell mailing list
[EMAIL PROTECTED]
http://www.haskell.org/mailman/listinfo/haskell
