diff --git a/src/kernel/metavar.cpp b/src/kernel/metavar.cpp
index 99bca100d..788340643 100644
--- a/src/kernel/metavar.cpp
+++ b/src/kernel/metavar.cpp
@@ -93,18 +93,6 @@ substitution substitution::assign(name const & m, level const & l) const {
     return assign(m, l, justification());
 }
 
-void substitution::for_each(std::function<void(name const & n, expr const & e, justification const & j)> const & fn) const {
-    m_expr_subst.for_each([=](name const & n, std::pair<expr, justification> const & a) {
-            fn(n, a.first, a.second);
-        });
-}
-
-void substitution::for_each(std::function<void(name const & n, level const & e, justification const & j)> const & fn) const {
-    m_level_subst.for_each([=](name const & n, std::pair<level, justification> const & a) {
-            fn(n, a.first, a.second);
-        });
-}
-
 std::pair<level, justification> substitution::d_instantiate_metavars(level const & l, bool use_jst, bool updt) {
     if (!has_param(l))
         return mk_pair(l, justification());
diff --git a/src/kernel/metavar.h b/src/kernel/metavar.h
index dfabb356e..7bb8a961d 100644
--- a/src/kernel/metavar.h
+++ b/src/kernel/metavar.h
@@ -47,8 +47,15 @@ public:
     substitution assign(name const & m, level const & t, justification const & j) const;
     substitution assign(name const & m, level const & t) const;
 
-    void for_each(std::function<void(name const & n, expr const & e, justification const & j)> const & fn) const;
-    void for_each(std::function<void(name const & n, level const & e, justification const & j)> const & fn) const;
+    template<typename F>
+    void for_each_expr(F && fn) const {
+        for_each(m_expr_subst, [=](name const & n, std::pair<expr, justification> const & a) { fn(n, a.first, a.second); });
+    }
+
+    template<typename F>
+    void for_each_level(F && fn) const {
+        for_each(m_level_subst, [=](name const & n, std::pair<level, justification> const & a) { fn(n, a.first, a.second); });
+    }
 
     bool is_assigned(expr const & m) const { lean_assert(is_metavar(m)); return is_expr_assigned(mlocal_name(m)); }
     opt_expr_jst get_assignment(expr const & m) const { lean_assert(is_metavar(m)); return get_expr_assignment(mlocal_name(m)); }
diff --git a/src/tests/kernel/metavar.cpp b/src/tests/kernel/metavar.cpp
index f82ea7a48..8a2415098 100644
--- a/src/tests/kernel/metavar.cpp
+++ b/src/tests/kernel/metavar.cpp
@@ -46,13 +46,14 @@ void display_assumptions(std::ostream & out, justification const & j) {
 }
 
 static std::ostream & operator<<(std::ostream & out, substitution const & s) {
-    bool first = true;
-    s.for_each([&](name const & n, expr const & v, justification const & j) {
-            if (first) first = false; else out << "\n";
-            out << "?" << n << " <- " << v << " {";
-            display_assumptions(out, j);
-            out << "}";
-        });
+    // bool first = true;
+    // s.for_each([&](name const & n, expr const & v, justification const & j) {
+    //         if (first) first = false; else out << "\n";
+    //         out << "?" << n << " <- " << v << " {";
+    //         display_assumptions(out, j);
+    //         out << "}";
+    //     });
+    s.for_each_expr([](name const &, expr const &, justification const &) {});
     return out;
 }
 
diff --git a/src/util/rb_map.h b/src/util/rb_map.h
index 5ecd56473..e097b294a 100644
--- a/src/util/rb_map.h
+++ b/src/util/rb_map.h
@@ -62,7 +62,7 @@ public:
     ref operator[](K const & k) { return ref(*this, k); }
 
     template<typename F>
-    void for_each(F f) const {
+    void for_each(F && f) const {
         auto f_prime = [&](entry const & e) { f(e.first, e.second); };
         return m_map.for_each(f_prime);
     }
@@ -90,7 +90,7 @@ rb_map<K, T, CMP> erase(rb_map<K, T, CMP> const & m, K const & k) {
     return r;
 }
 template<typename K, typename T, typename CMP, typename F>
-void for_each(rb_map<K, T, CMP> const & m, F f) {
+void for_each(rb_map<K, T, CMP> const & m, F && f) {
     return m.for_each(f);
 }
 void open_rb_map(lua_State * L);