4 When matching the contexts of the signatures for `f' and `g'
5 (the signature contexts in a mutually recursive group should all be identical)
8 Cannot unify the type-signature variable `c'
9 with the type `a -> b -> b'
10 Expected type: a -> b -> b
12 In the first argument of `f', namely `c'
13 In the first argument of `foldr', namely `(f c)'
15 Compilation had errors