Implement str() and repr() builtin functions.
diff --git a/py/builtin.h b/py/builtin.h
index 3401528..0716b95 100644
--- a/py/builtin.h
+++ b/py/builtin.h
@@ -23,3 +23,5 @@
 MP_DECLARE_CONST_FUN_OBJ(mp_builtin_range_obj);
 MP_DECLARE_CONST_FUN_OBJ(mp_builtin_sorted_obj);
 MP_DECLARE_CONST_FUN_OBJ(mp_builtin_sum_obj);
+MP_DECLARE_CONST_FUN_OBJ(mp_builtin_str_obj);
+MP_DECLARE_CONST_FUN_OBJ(mp_builtin_repr_obj);