- -- DERIVING CHECK
- -- It is obviously illegal to have an explicit instance
- -- for something that we are also planning to `derive'
- | maybeToBool alg_tycon_app_maybe && clas `elem` (tyConDerivings alg_tycon)
- -> addErrTc (derivingWhenInstanceExistsErr clas first_inst_tau)
- -- Kind check will have ensured inst_taus is of length 1
-