T7558.hs:8:4:
Couldn't match type ‘a’ with ‘Maybe a’
‘a’ is a rigid type variable bound by
the type signature for: f :: T a a -> Bool at T7558.hs:7:6
Inaccessible code in
a pattern with constructor:
MkT :: forall a b. (a ~ Maybe b) => a -> Maybe b -> T a b,
in an equation for ‘f’
Relevant bindings include
f :: T a a -> Bool (bound at T7558.hs:8:1)
In the pattern: MkT x y
In an equation for ‘f’: f (MkT x y) = [x, y] `seq` True