
T1897a.hs:9:1:
    Ambiguous type variable `a0' in the constraint:
      (Wob a0 b) arising from the ambiguity check for `foo'
    Probable fix: add a type signature that fixes these type variable(s)
    When checking that `foo'
      has the inferred type `forall a b. Wob a b => b -> [b]'
    Probable cause: the inferred type is ambiguous
