-- | Like 'tcLookupDataFamInst_maybe', but returns the arguments back if
-- there is no data family to unwrap.
-- Returns a Representational coercion
tcLookupDataFamInst :: FamInstEnvs -> TyCon -> [TcType]
                    -> (TyCon, [TcType], Coercion)
tcLookupDataFamInst fam_inst_envs tc tc_args
  | Just (rep_tc, rep_args, co)
      <- tcLookupDataFamInst_maybe fam_inst_envs tc tc_args
  = (rep_tc, rep_args, co)
  | otherwise
  = (tc, tc_args, mkRepReflCo (mkTyConApp tc tc_args))
tcLookupDataFamInst :: FamInstEnvs -> TyCon -> [TcType]
                    -> (TyCon, [TcType], Coercion)
tcLookupDataFamInst fam_inst_envs tc tc_args
  | Just (rep_tc, rep_args, co)
      <- tcLookupDataFamInst_maybe fam_inst_envs tc tc_args
  = (rep_tc, rep_args, co)
  | otherwise
  = (tc, tc_args, mkRepReflCo (mkTyConApp tc tc_args))
tcLookupDataFamInst fam_inst_envs tc tc_args
  | Just (rep_tc, rep_args, co)
      <- tcLookupDataFamInst_maybe fam_inst_envs tc tc_args
  = (rep_tc, rep_args, co)
  | otherwise
  = (tc, tc_args, mkRepReflCo (mkTyConApp tc tc_args))