From 56efc969fd391edc272f424c8d00d978a3e56b46 Mon Sep 17 00:00:00 2001
From: Daniel Selsam <daniel.selsam@gmail.com>
Date: Mon, 16 Nov 2015 17:48:19 -0800
Subject: [PATCH] feat(library/simplifier/simp_rule_set): throw exception for
 null simp rule

---
 src/library/simplifier/simp_rule_set.cpp | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/library/simplifier/simp_rule_set.cpp b/src/library/simplifier/simp_rule_set.cpp
index c6581c492..b56f68c82 100644
--- a/src/library/simplifier/simp_rule_set.cpp
+++ b/src/library/simplifier/simp_rule_set.cpp
@@ -259,6 +259,7 @@ static name * g_prefix = nullptr;
 simp_rule_sets add_core(tmp_type_context & tctx, simp_rule_sets const & s,
                         name const & id, levels const & univ_metas, expr const & e, expr const & h) {
     list<expr_pair> ceqvs   = to_ceqvs(tctx, e, h);
+    if (is_nil(ceqvs)) throw exception("[simp] rule invalid");
     environment const & env = tctx.env();
     simp_rule_sets new_s = s;
     for (expr_pair const & p : ceqvs) {