-ruleLhsTvs (OpApp e1 op _ e2)
- = ruleLhsTvs e1 `unionVarSet` ruleLhsTvs op `unionVarSet` ruleLhsTvs e2
-ruleLhsTvs (HsApp e1 e2)
- = ruleLhsTvs e1 `unionVarSet` ruleLhsTvs e2
-ruleLhsTvs (HsVar v) = emptyVarSet -- I don't think we need the tyvars of the Id
-ruleLhsTvs (TyApp e1 tys)
- = ruleLhsTvs e1 `unionVarSet` tyVarsOfTypes tys
+-- Uh oh! validRuleLhs only checks the function part of rule LHSs!
+
+ruleLhsTvs (HsPar e) = ruleLhsTvs e
+ruleLhsTvs (HsLit e) = emptyVarSet
+ruleLhsTvs (HsOverLit e) = emptyVarSet
+ruleLhsTvs (HsVar v) = emptyVarSet -- I don't think we need the tyvars of the Id
+
+ruleLhsTvs (OpApp e1 op _ e2) = ruleLhsTvs e1 `unionVarSet` ruleLhsTvs op
+ `unionVarSet` ruleLhsTvs e2
+ruleLhsTvs (HsApp e1 e2) = ruleLhsTvs e1 `unionVarSet` ruleLhsTvs e2
+ruleLhsTvs (TyApp e1 tys) = ruleLhsTvs e1 `unionVarSet` tyVarsOfTypes tys
+ruleLhsTvs (DictApp e ds) = ruleLhsTvs e
+ruleLhsTvs (NegApp e _) = ruleLhsTvs e
+ruleLhsTvs (ExplicitList ty es) = tyVarsOfType ty `unionVarSet` ruleLhsTvs_s es
+ruleLhsTvs (ExplicitTuple es _) = ruleLhsTvs_s es
+
+-- Type abstractions can occur in rules like
+-- "foldr k z (build g) = g k z"
+ruleLhsTvs (TyLam tvs e) = ruleLhsTvs e `delVarSetList` tvs
+ruleLhsTvs (DictLam ids e) = ruleLhsTvs e