T1897a.hs:9:1: error:
    • Could not deduce (Wob a0 b)
      from the context: Wob a b
        bound by the inferred type for ‘foo’:
                   forall {a} {b}. Wob a b => b -> [b]
        at T1897a.hs:9:1-24
      The type variable ‘a0’ is ambiguous
    • In the ambiguity check for the inferred type for ‘foo’
      To defer the ambiguity check to use sites, enable AllowAmbiguousTypes
      When checking the inferred type
        foo :: forall {a} {b}. Wob a b => b -> [b]