18 Aug
2002
18 Aug
'02
10:26 p.m.
At 2002-08-18 18:19, Scott J. wrote:
A question: s is not a type variable as a isn't it?
Both are quantified type variables. But only one of those quantifiers can be placed at the top level of the expression. runST :: forall a. ((forall s. ST s a) -> a)
I mean a can be of type Integer while s cannot.
Well yes, you can specialise "forall a" to Integer. So runST can be specialised to this type: runST ::[special] (forall s. ST s Integer) -> Integer ...whereas you cannot specialise "s" in the same way. Think of it in terms of logic, if for all a: f(a), then by simple specialisation f(Integer). -- Ashley Yakeley, Seattle WA