Roles12.hs:6:1: error:
    Type constructor ‘T’ has conflicting definitions in the module
    and its hs-boot file
    Main module: type role T phantom
                 type T :: * -> *
                 data T a
    Boot file:   type T :: * -> *
                 data T a
    The roles do not match.
    Roles on abstract types default to ‘representational’ in boot files.