rnfail020.hs:12:
- The constraint `Eq a' does not mention any of the universally quantified type variables
- in the type `(Eq a) => Set a -> Set a -> Set a'
+ All of the type variables in the constraint `Eq a' are already in scope
+ At least one must be universally quantified here
+ In the type `(Eq a) => Set a -> Set a -> Set a'
In a type signature for `unionSets'
- In an equation for function `unionSetB':
+ In the definition of `unionSetB':
unionSetB (s1 :: Set a) s2
= unionSets s1 s2
where