Add hint to overloading errors
The definition
main = snd (x, True) where x free
produces the following error message:
Ambiguous type variable _3
in type Prelude.Data _3 => Prelude.Bool
Since this is difficult to understand for newbies, maybe the front end can add a hint for such cases, i.e., when a type variable is ambiguous but does not occur in the top-level type expression. E.g.:
Hint: add type annotation to local variable or declaration