[Haskell-cafe] Puzzled by error with forall quantifier.
Theodore S. Norvell
theo at engr.mun.ca
Mon Feb 2 15:59:18 EST 2004
Can anyone explain the following error message from Hug98
(with extensions enabled)?
> class Space t
> class Space t => HasY v t
> assignY :: v -> t -> t
> getY :: t -> v
> varY :: forall w . Space w => v -> (t->t) -> (w->w)
I get an error on the last definition "quantifier does not
mention type variable v" (and if I quantify v, then it complains
that t is not quantified).
The idea I'm trying to express is that for any instance of HasY v t
there should be a function varY with type
v -> (t->t) -> (w->w)
for some type w of class Space.
Any help much appreciated.
Is there any kind of tutorial introduction to "forall" out there?
More information about the Haskell-Cafe