[1 of 1] Compiling ShouldFail[sig of Prelude] ( tcfail220.hsig, nothing )

tcfail220.hsig:4:1: error:
    Type constructor ‘Either’ has conflicting definitions in the module
    and its hsig file
    Main module: data Either a b = Left a | Right b
    Hsig file:  type role Either representational phantom phantom
                data Either a b c = Left a
    The types have different kinds