Implement str() and repr() builtin functions.
diff --git a/py/builtin.c b/py/builtin.c
index a45b146..bc10f29 100644
--- a/py/builtin.c
+++ b/py/builtin.c
@@ -338,3 +338,19 @@
     return self;
 }
 MP_DEFINE_CONST_FUN_OBJ_KW(mp_builtin_sorted_obj, 1, mp_builtin_sorted);
+
+mp_obj_t mp_builtin_str(mp_obj_t o) {
+    vstr_t *vstr = vstr_new();
+    mp_obj_print_helper(vstr_printf_wrapper, vstr, o, PRINT_STR);
+    return mp_obj_new_str(qstr_from_str_take(vstr->buf, vstr->alloc));
+}
+
+MP_DEFINE_CONST_FUN_OBJ_1(mp_builtin_str_obj, mp_builtin_str);
+
+mp_obj_t mp_builtin_repr(mp_obj_t o) {
+    vstr_t *vstr = vstr_new();
+    mp_obj_print_helper(vstr_printf_wrapper, vstr, o, PRINT_REPR);
+    return mp_obj_new_str(qstr_from_str_take(vstr->buf, vstr->alloc));
+}
+
+MP_DEFINE_CONST_FUN_OBJ_1(mp_builtin_repr_obj, mp_builtin_repr);
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);
diff --git a/py/misc.h b/py/misc.h
index e985bc5..8c2c854 100644
--- a/py/misc.h
+++ b/py/misc.h
@@ -81,6 +81,8 @@
 //void vstr_add_le32(vstr_t *vstr, unsigned int v);
 void vstr_cut_tail(vstr_t *vstr, int len);
 void vstr_printf(vstr_t *vstr, const char *fmt, ...);
+// TODO: do we need wrapper at all?
+void vstr_printf_wrapper(void *env, const char *fmt, ...);
 
 #ifdef va_start
 void vstr_vprintf(vstr_t *vstr, const char *fmt, va_list ap);
diff --git a/py/mpqstrraw.h b/py/mpqstrraw.h
index c3cda84..615c9da 100644
--- a/py/mpqstrraw.h
+++ b/py/mpqstrraw.h
@@ -56,9 +56,11 @@
 Q(pow)
 Q(print)
 Q(range)
+Q(repr)
 Q(set)
 Q(sorted)
 Q(sum)
+Q(str)
 Q(tuple)
 Q(type)
 Q(zip)
diff --git a/py/runtime.c b/py/runtime.c
index 3d8f0c9..3f75957 100644
--- a/py/runtime.c
+++ b/py/runtime.c
@@ -136,6 +136,8 @@
     mp_map_add_qstr(&map_builtins, MP_QSTR_range, (mp_obj_t)&mp_builtin_range_obj);
     mp_map_add_qstr(&map_builtins, MP_QSTR_sorted, (mp_obj_t)&mp_builtin_sorted_obj);
     mp_map_add_qstr(&map_builtins, MP_QSTR_sum, (mp_obj_t)&mp_builtin_sum_obj);
+    mp_map_add_qstr(&map_builtins, MP_QSTR_str, (mp_obj_t)&mp_builtin_str_obj);
+    mp_map_add_qstr(&map_builtins, MP_QSTR_repr, (mp_obj_t)&mp_builtin_repr_obj);
 
     next_unique_code_id = 1; // 0 indicates "no code"
     unique_codes_alloc = 0;