import HsSyn ( Pat(..), LPat, HsConDetails(..) )
import DsBinds ( dsLHsBinds )
-import DataCon ( DataCon, dataConInstOrigArgTys,
+import DataCon ( DataCon, dataConInstOrigArgTys, dataConEqSpec,
dataConFieldLabels, dataConSourceArity )
import TcType ( tcTyConAppArgs )
import Type ( mkTyVarTys )
pat_tvs = tvs1, pat_dicts = dicts1 } = firstPat eqn1
arg_tys = dataConInstOrigArgTys con inst_tys
- inst_tys = tcTyConAppArgs pat_ty1 ++ mkTyVarTys tvs1
+ n_co_args = length (dataConEqSpec con)
+ inst_tys = tcTyConAppArgs pat_ty1 ++ (drop n_co_args $ mkTyVarTys tvs1)
-- Newtypes opaque, hence tcTyConAppArgs
shift eqn@(EqnInfo { eqn_pats = ConPatOut{ pat_tvs = tvs, pat_dicts = ds,