diff --git a/src/item.cc b/src/item.cc
index 5262d1db..17d46652 100644
--- a/src/item.cc
+++ b/src/item.cc
@@ -398,6 +398,13 @@ value_t get_comment(item_t& item)
   }
 }
 
+void item_t::define(const symbol_t::kind_t, const string& name,
+                    expr_t::ptr_op_t def)
+{
+  bind_scope_t bound_scope(*scope_t::default_scope, *this);
+  set_tag(name, def->calc(bound_scope));
+}
+
 expr_t::ptr_op_t item_t::lookup(const symbol_t::kind_t kind,
                                 const string& name)
 {
diff --git a/src/item.h b/src/item.h
index c56fba27..8d9a79ee 100644
--- a/src/item.h
+++ b/src/item.h
@@ -216,6 +216,8 @@ public:
     return _state;
   }
 
+  virtual void define(const symbol_t::kind_t, const string&,
+                      expr_t::ptr_op_t);
   virtual expr_t::ptr_op_t lookup(const symbol_t::kind_t kind,
                                   const string& name);