11 Aug
2005
11 Aug
'05
8:04 p.m.
Hello,
On 8/11/05, Simon Peyton-Jones
... Here is a boiled down version, much simpler to understand.
module Proxy where
class Dep a b | a -> b instance Dep Char Bool
foo :: forall a. a -> (forall b. Dep a b => a -> b) -> Int foo x f = error "urk"
Should this really be valid? It seems that because 'b' is determined by 'a' we should not be allowed to quantify over 'b' without quantifying over 'a'. I think we can view the class 'Dep' as a function on types, that is defined by the instances. Then the above type is: a -> (a -> Dep a) -> Int and it seems that the quantification over 'b' is non-sensical. -Iavor