mkArbitraryTypeEnv :: [TyVar] -> [([TyVar], a, b, c)] -> DsM (TyVarEnv Type)
-- If any of the tyvars is missing from any of the lists in
-- the second arg, return a binding in the result
mkArbitraryTypeEnv :: [TyVar] -> [([TyVar], a, b, c)] -> DsM (TyVarEnv Type)
-- If any of the tyvars is missing from any of the lists in
-- the second arg, return a binding in the result