objsingleton: New home for Ellipsis and NotImplemented.

Having NotImplemented as MP_OBJ_SENTINEL turned out to be problematic
(it needs to be checked for in a lot of places, otherwise it'll crash
as would pass MP_OBJ_IS_OBJ()), so made a proper singleton value like
Ellipsis, both of them sharing the same type.

py/modbuiltins.c

@@ -635,7 +635,7 @@ STATIC const mp_map_elem_t mp_module_builtins_globals_table[] = {
     // built-in objects
     { MP_OBJ_NEW_QSTR(MP_QSTR_Ellipsis), (mp_obj_t)&mp_const_ellipsis_obj },
     #if MICROPY_PY_BUILTINS_NOTIMPLEMENTED
-    { MP_OBJ_NEW_QSTR(MP_QSTR_NotImplemented), MP_OBJ_SENTINEL },
+    { MP_OBJ_NEW_QSTR(MP_QSTR_NotImplemented), (mp_obj_t)&mp_const_notimplemented_obj },
     #endif
 
     // built-in user functions

py/obj.c

@@ -62,14 +62,6 @@ void mp_obj_print_helper(const mp_print_t *print, mp_obj_t o_in, mp_print_kind_t
         return;
     }
 #endif
-
-    #if MICROPY_PY_BUILTINS_NOTIMPLEMENTED
-    if (o_in == MP_OBJ_SENTINEL) {
-        mp_printf(print, "%q", MP_QSTR_NotImplemented);
-        return;
-    }
-    #endif
-
     mp_obj_type_t *type = mp_obj_get_type(o_in);
     if (type->print != NULL) {
         type->print((mp_print_t*)print, o_in, kind);

py/obj.h

@@ -449,7 +449,8 @@ extern const struct _mp_obj_bool_t mp_const_false_obj;
 extern const struct _mp_obj_bool_t mp_const_true_obj;
 extern const struct _mp_obj_str_t mp_const_empty_bytes_obj;
 extern const struct _mp_obj_tuple_t mp_const_empty_tuple_obj;
-extern const struct _mp_obj_ellipsis_t mp_const_ellipsis_obj;
+extern const struct _mp_obj_singleton_t mp_const_ellipsis_obj;
+extern const struct _mp_obj_singleton_t mp_const_notimplemented_obj;
 extern const struct _mp_obj_exception_t mp_const_MemoryError_obj;
 extern const struct _mp_obj_exception_t mp_const_GeneratorExit_obj;
 

py/objsingleton.c

@@ -0,0 +1,57 @@
+/*
+ * This file is part of the Micro Python project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2013, 2014 Damien P. George
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include <stdlib.h>
+#include <assert.h>
+
+#include "py/nlr.h"
+#include "py/obj.h"
+#include "py/runtime0.h"
+
+/******************************************************************************/
+/* singleton objects defined by Python                                        */
+
+typedef struct _mp_obj_singleton_t {
+    mp_obj_base_t base;
+    qstr name;
+} mp_obj_singleton_t;
+
+STATIC void singleton_print(const mp_print_t *print, mp_obj_t self_in, mp_print_kind_t kind) {
+    (void)kind;
+    mp_obj_singleton_t *self = self_in;
+    mp_printf(print, "%q", self->name);
+}
+
+const mp_obj_type_t mp_type_singleton = {
+    { &mp_type_type },
+    .name = MP_QSTR_,
+    .print = singleton_print,
+};
+
+const mp_obj_singleton_t mp_const_ellipsis_obj = {{&mp_type_singleton}, MP_QSTR_Ellipsis};
+#if MICROPY_PY_BUILTINS_NOTIMPLEMENTED
+const mp_obj_singleton_t mp_const_notimplemented_obj = {{&mp_type_singleton}, MP_QSTR_NotImplemented};
+#endif

py/objslice.c

@@ -31,27 +31,6 @@
 #include "py/obj.h"
 #include "py/runtime0.h"
 
-/******************************************************************************/
-/* ellipsis object, a singleton                                               */
-
-typedef struct _mp_obj_ellipsis_t {
-    mp_obj_base_t base;
-} mp_obj_ellipsis_t;
-
-STATIC void ellipsis_print(const mp_print_t *print, mp_obj_t self_in, mp_print_kind_t kind) {
-    (void)self_in;
-    (void)kind;
-    mp_print_str(print, "Ellipsis");
-}
-
-const mp_obj_type_t mp_type_ellipsis = {
-    { &mp_type_type },
-    .name = MP_QSTR_Ellipsis,
-    .print = ellipsis_print,
-};
-
-const mp_obj_ellipsis_t mp_const_ellipsis_obj = {{&mp_type_ellipsis}};
-
 /******************************************************************************/
 /* slice object                                                               */
 

py/py.mk

@@ -82,6 +82,7 @@ PY_O_BASENAME = \
 	objrange.o \
 	objreversed.o \
 	objset.o \
+	objsingleton.o \
 	objslice.o \
 	objstr.o \
 	objstrunicode.o \