diff --git a/include/chaiscript/dispatchkit/bootstrap.hpp b/include/chaiscript/dispatchkit/bootstrap.hpp
index 114a99a..5cf0f48 100644
--- a/include/chaiscript/dispatchkit/bootstrap.hpp
+++ b/include/chaiscript/dispatchkit/bootstrap.hpp
@@ -558,7 +558,7 @@ namespace chaiscript
     template<typename Type>
     Boxed_Value ptr_assign(Boxed_Value lhs, const boost::shared_ptr<typename boost::add_const<Type>::type> &rhs)
     {
-      if (lhs.is_unknown() 
+      if (lhs.is_undef() 
           || (!lhs.get_type_info().is_const() && lhs.get_type_info().bare_equal(chaiscript::detail::Get_Type_Info<Type>::get())))
       {
         lhs.assign(Boxed_Value(rhs));
@@ -580,7 +580,7 @@ namespace chaiscript
       */
       static Boxed_Value unknown_assign(Boxed_Value lhs, Boxed_Value rhs)
       {
-        if (lhs.is_unknown())
+        if (lhs.is_undef())
         {
           return (lhs.assign(rhs));
         } else {
@@ -708,6 +708,7 @@ namespace chaiscript
         m->add(fun(&Dynamic_Object::get_attr), "get_attr");
         m->eval("def Dynamic_Object::clone() { var new_o := Dynamic_Object(this.get_type_name()); for_each(this.get_attrs(), bind(fun(new_o, x) { new_o.get_attr(x.first) = x.second; }, new_o, _) ); return new_o; }");
 
+        m->add(fun(&Boxed_Value::is_undef), "is_undef");
 
         basic_constructors<bool>("bool", m);
         oper_assign<std::string>(m);
diff --git a/include/chaiscript/dispatchkit/boxed_value.hpp b/include/chaiscript/dispatchkit/boxed_value.hpp
index 9a6bc56..e4b5c3b 100644
--- a/include/chaiscript/dispatchkit/boxed_value.hpp
+++ b/include/chaiscript/dispatchkit/boxed_value.hpp
@@ -293,9 +293,9 @@ namespace chaiscript
       /**
        * return true if the object is uninitialized
        */
-      bool is_unknown() const
+      bool is_undef() const
       {
-        return m_data->m_type_info.is_unknown();
+        return m_data->m_type_info.is_undef();
       }
 
       boost::any get() const
@@ -594,7 +594,7 @@ namespace chaiscript
     Boxed_POD_Value(const Boxed_Value &v)
       : d(0), i(0), m_isfloat(false)
     {
-      if (v.get_type_info().is_unknown())
+      if (v.get_type_info().is_undef())
       {
         throw boost::bad_any_cast();
       }
diff --git a/include/chaiscript/dispatchkit/proxy_functions.hpp b/include/chaiscript/dispatchkit/proxy_functions.hpp
index 4f3b641..ebd85b9 100644
--- a/include/chaiscript/dispatchkit/proxy_functions.hpp
+++ b/include/chaiscript/dispatchkit/proxy_functions.hpp
@@ -92,7 +92,7 @@ namespace chaiscript
 
             const Type_Info &ti = types[1];
 
-            if (ti.is_unknown() || vals[0].get_type_info().is_unknown()
+            if (ti.is_undef() || vals[0].get_type_info().is_undef()
                 || ti.bare_equal(user_type<Boxed_Value>())
                 || ti.bare_equal(user_type<Boxed_POD_Value>())
                 || ti.bare_equal(vals[0].get_type_info()))
diff --git a/include/chaiscript/dispatchkit/type_info.hpp b/include/chaiscript/dispatchkit/type_info.hpp
index f16094c..3b3eb49 100644
--- a/include/chaiscript/dispatchkit/type_info.hpp
+++ b/include/chaiscript/dispatchkit/type_info.hpp
@@ -29,14 +29,14 @@ namespace chaiscript
         : m_is_const(t_is_const), m_is_reference(t_is_reference), m_is_pointer(t_is_pointer),
         m_is_void(t_is_void),
         m_type_info(t_ti), m_bare_type_info(t_bareti),
-        m_is_unknown(false)
+        m_is_undef(false)
       {
       }
 
       Type_Info()
         : m_is_const(false), m_is_reference(false), m_is_pointer(false),
         m_is_void(false), m_type_info(0), m_bare_type_info(0),
-        m_is_unknown(true)
+        m_is_undef(true)
       {
       }
 
@@ -45,7 +45,7 @@ namespace chaiscript
         m_is_pointer(ti.m_is_pointer),
         m_is_void(ti.m_is_void), m_type_info(ti.m_type_info), 
         m_bare_type_info(ti.m_bare_type_info),
-        m_is_unknown(ti.m_is_unknown)
+        m_is_undef(ti.m_is_undef)
       {
       }
 
@@ -57,7 +57,7 @@ namespace chaiscript
         m_is_void = ti.m_is_void;
         m_type_info = ti.m_type_info;
         m_bare_type_info = ti.m_bare_type_info;
-        m_is_unknown = ti.m_is_unknown;
+        m_is_undef = ti.m_is_undef;
         return *this;
       }
 
@@ -86,7 +86,7 @@ namespace chaiscript
       bool is_const() const { return m_is_const; }
       bool is_reference() const { return m_is_reference; }
       bool is_void() const { return m_is_void; }
-      bool is_unknown() const { return m_is_unknown || m_bare_type_info == 0; }
+      bool is_undef() const { return m_is_undef || m_bare_type_info == 0; }
 
       std::string bare_name() const
       {
@@ -105,7 +105,7 @@ namespace chaiscript
       bool m_is_void;
       const std::type_info *m_type_info;
       const std::type_info *m_bare_type_info;
-      bool m_is_unknown;
+      bool m_is_undef;
   };
 
   namespace detail
diff --git a/include/chaiscript/language/chaiscript_eval.hpp b/include/chaiscript/language/chaiscript_eval.hpp
index 8862895..3a639db 100644
--- a/include/chaiscript/language/chaiscript_eval.hpp
+++ b/include/chaiscript/language/chaiscript_eval.hpp
@@ -171,7 +171,7 @@ namespace chaiscript
                     Boxed_Value lhs = eval_token(ss, node->children[i]);
 
                     try {
-                        if (lhs.is_unknown())
+                        if (lhs.is_undef())
                         {
                           retval = ss.call_function("clone", Param_List_Builder() << retval);
                         }
@@ -191,7 +191,7 @@ namespace chaiscript
                 }
                 else if (node->children[i+1]->text == ":=") {
                     Boxed_Value lhs = eval_token(ss, node->children[i]);
-                    if (lhs.is_unknown() || type_match(lhs, retval)) {
+                    if (lhs.is_undef() || type_match(lhs, retval)) {
                         lhs.assign(retval);
                     }
                     else {
diff --git a/unittests/is_undef.chai b/unittests/is_undef.chai
new file mode 100644
index 0000000..384761d
--- /dev/null
+++ b/unittests/is_undef.chai
@@ -0,0 +1,4 @@
+var i;
+print(i.is_undef());
+i = 5;
+print(i.is_undef());
diff --git a/unittests/is_undef.txt b/unittests/is_undef.txt
new file mode 100644
index 0000000..da29283
--- /dev/null
+++ b/unittests/is_undef.txt
@@ -0,0 +1,2 @@
+true
+false