diff --git a/include/pocketpy/common/strname.h b/include/pocketpy/common/strname.h
index 10991d41..eece32d5 100644
--- a/include/pocketpy/common/strname.h
+++ b/include/pocketpy/common/strname.h
@@ -9,6 +9,8 @@ extern "C" {
 
 typedef uint16_t StrName;
 
+#define py_name(name) pk_StrName__map(#name)
+
 uint16_t pk_StrName__map(const char*);
 uint16_t pk_StrName__map2(c11_string);
 const char* pk_StrName__rmap(uint16_t index);
diff --git a/include/pocketpy/interpreter/frame.h b/include/pocketpy/interpreter/frame.h
index ce06e2c5..692893f6 100644
--- a/include/pocketpy/interpreter/frame.h
+++ b/include/pocketpy/interpreter/frame.h
@@ -11,7 +11,7 @@
 extern "C" {
 #endif
 
-PyVar* FastLocals__try_get_by_name(PyVar* locals, const CodeObject* co, StrName name);
+PyVar* FastLocals__try_get_by_name(PyVar* locals, const CodeObject* co, py_Name name);
 pk_NameDict* FastLocals__to_namedict(PyVar* locals, const CodeObject* co);
 
 typedef struct ValueStack {
@@ -46,7 +46,7 @@ typedef struct Frame {
 } Frame;
 
 
-Frame* Frame__new(const CodeObject* co, PyObject* module, PyObject* function, PyVar* p0, PyVar* locals, const CodeObject* locals_co);
+Frame* Frame__new(const CodeObject* co, const PyVar* module, const PyVar* function, PyVar* p0, PyVar* locals, const CodeObject* locals_co);
 void Frame__delete(Frame* self);
 
 PK_INLINE int Frame__ip(const Frame* self){
@@ -64,14 +64,14 @@ PK_INLINE int Frame__iblock(const Frame* self){
 }
 
 PK_INLINE pk_NameDict* Frame__f_globals(Frame* self){
-    return self->module->dict;
+    return PyObject__dict(self->module);
 }
 
-PK_INLINE PyVar* Frame__f_globals_try_get(Frame* self, StrName name){
-    return pk_NameDict__try_get(self->module->dict, name);
+PK_INLINE PyVar* Frame__f_globals_try_get(Frame* self, py_Name name){
+    return pk_NameDict__try_get(Frame__f_globals(self), name);
 }
 
-PyVar* Frame__f_closure_try_get(Frame* self, StrName name);
+PyVar* Frame__f_closure_try_get(Frame* self, py_Name name);
 
 int Frame__prepare_jump_exception_handler(Frame* self, ValueStack*);
 void Frame__prepare_jump_break(Frame* self, ValueStack*, int);
diff --git a/include/pocketpy/interpreter/gc.h b/include/pocketpy/interpreter/gc.h
index 355b34c7..6f8fa221 100644
--- a/include/pocketpy/interpreter/gc.h
+++ b/include/pocketpy/interpreter/gc.h
@@ -28,8 +28,8 @@ void pk_ManagedHeap__collect_if_needed(pk_ManagedHeap* self);
 int pk_ManagedHeap__collect(pk_ManagedHeap* self);
 int pk_ManagedHeap__sweep(pk_ManagedHeap* self);
 
-PyObject* pk_ManagedHeap__new(pk_ManagedHeap* self, Type type, int size);
-PyObject* pk_ManagedHeap__gcnew(pk_ManagedHeap* self, Type type, int size);
+PyObject* pk_ManagedHeap__new(pk_ManagedHeap* self, Type type, int slots, int size);
+PyObject* pk_ManagedHeap__gcnew(pk_ManagedHeap* self, Type type, int slots, int size);
 
 // external implementation
 void pk_ManagedHeap__mark(pk_ManagedHeap* self);
diff --git a/include/pocketpy/interpreter/vm.h b/include/pocketpy/interpreter/vm.h
index b25fcda7..6b00cbb4 100644
--- a/include/pocketpy/interpreter/vm.h
+++ b/include/pocketpy/interpreter/vm.h
@@ -9,7 +9,7 @@ extern "C" {
 #endif
 
 typedef struct pk_TypeInfo{
-    StrName name;
+    py_Name name;
     Type base;
 
     PyVar self;      // the type object itself
@@ -38,7 +38,7 @@ typedef struct pk_TypeInfo{
     py_CFunction on_end_subclass;   // for enum module
 } pk_TypeInfo;
 
-void pk_TypeInfo__ctor(pk_TypeInfo* self, StrName name, Type base, PyObject* obj, const PyVar* module, bool subclass_enabled);
+void pk_TypeInfo__ctor(pk_TypeInfo* self, py_Name name, Type base, PyObject* obj, const PyVar* module, bool subclass_enabled);
 void pk_TypeInfo__dtor(pk_TypeInfo* self);
 
 typedef struct pk_VM {
diff --git a/include/pocketpy/objects/object.h b/include/pocketpy/objects/object.h
index 04f39fca..1824fb2d 100644
--- a/include/pocketpy/objects/object.h
+++ b/include/pocketpy/objects/object.h
@@ -11,17 +11,24 @@ typedef struct PyObject{
     Type type;          // we have a duplicated type here for convenience
     bool gc_is_large;
     bool gc_marked;
-    pk_NameDict* dict;  // gc will delete this on destruction
+    int slots;          // number of slots in the object
 } PyObject;
 
-static_assert(sizeof(PyObject) <= 16, "!(sizeof(PyObject) <= 16)");
+// slots >= 0, allocate N slots
+// slots == -1, allocate a dict
 
-#define PyObject__value_ptr(self)   ((char*)self + 16)
-#define PyObject__as(T, self)       (T*)(PyObject__value_ptr(self))
-#define PK_OBJ_GET(T, val)          (*(T*)(PyObject__value_ptr((val)._obj)))
-#define PK_OBJ_SIZEOF(T)            (sizeof(T) + 16)
+// | 8 bytes HEADER | <N slots> | <value>
+// | 8 bytes HEADER | <dict>    | <value>
 
-PyObject* PyObject__new(Type type, int size);
+static_assert(sizeof(PyObject) <= 8, "!(sizeof(PyObject) <= 8)");
+
+PyVar* PyObject__slots(PyObject* self);
+pk_NameDict* PyObject__dict(PyObject* self);
+void* PyObject__value(PyObject* self);
+
+#define PK_OBJ_HEADER_SIZE(slots) ((slots)>=0 ? 8+sizeof(PyVar)*(slots) : 8+sizeof(pk_NameDict))
+
+PyObject* PyObject__new(Type type, int slots, int size);
 void PyObject__delete(PyObject* self);
 
 PK_INLINE PyVar PyVar__fromobj(PyObject* obj){
diff --git a/include/pocketpy/pocketpy.h b/include/pocketpy/pocketpy.h
index c58680f1..7dad4e33 100644
--- a/include/pocketpy/pocketpy.h
+++ b/include/pocketpy/pocketpy.h
@@ -10,7 +10,14 @@ extern "C" {
 typedef struct PyObject PyObject;
 typedef struct PyVar PyVar;
 typedef struct pk_VM pk_VM;
-typedef struct py_Error py_Error;
+typedef uint16_t py_Name;
+typedef int16_t Type;
+typedef PyVar* py_Ref;
+typedef int (*py_CFunction)(const py_Ref, int);
+
+typedef struct py_Error{
+    Type type;
+} py_Error;
 
 typedef enum BindType {
     BindType_FUNCTION,
@@ -18,55 +25,76 @@ typedef enum BindType {
     BindType_CLASSMETHOD,
 } BindType;
 
-typedef int (*py_CFunction)(const PyVar*, int);
 
-typedef uint16_t StrName;
-typedef int16_t Type;
 
 extern pk_VM* pk_current_vm;
 
+
 void py_initialize();
 // void py_switch_vm(const char* name);
 void py_finalize();
 
-py_Error* py_exec_simple(const char*);
-py_Error* py_eval_simple(const char*, PyVar*);
+int py_exec_simple(const char*);
+int py_eval_simple(const char*, py_Ref);
 
 /* py_error */
-void py_Error__print(const py_Error*);
-void py_Error__delete(py_Error*);
+py_Error* py_getlasterror();
+void py_Error__print(py_Error*);
 
-int py_eq(const PyVar*, const PyVar*);
-int py_le(const PyVar*, const PyVar*);
-int py_hash(const PyVar*, int64_t* out);
+int py_eq(const py_Ref, const py_Ref);
+int py_le(const py_Ref, const py_Ref);
+int py_hash(const py_Ref, int64_t* out);
 
 /* py_var */
-void py_new_int(PyVar*, int64_t);
-void py_new_float(PyVar*, double);
-void py_new_bool(PyVar*, bool);
-void py_new_str(PyVar*, const char*);
-void py_new_strn(PyVar*, const char*, int);
-void py_new_fstr(PyVar*, const char*, ...);
-void py_new_bytes(PyVar*, const uint8_t*, int);
-void py_new_none(PyVar*);
-void py_new_null(PyVar*);
+void py_new_int(py_Ref, int64_t);
+void py_new_float(py_Ref, double);
+void py_new_bool(py_Ref, bool);
+void py_new_str(py_Ref, const char*);
+void py_new_strn(py_Ref, const char*, int);
+void py_new_fstr(py_Ref, const char*, ...);
+void py_new_bytes(py_Ref, const uint8_t*, int);
+void py_new_none(py_Ref);
+void py_new_null(py_Ref);
+
+void py_new_tuple(PyVar, int);
 
 // new style decl-based function
-void py_new_function(PyVar*, py_CFunction, const char* sig, BindType bt);
-void py_new_function2(PyVar*, py_CFunction, const char* sig, BindType bt, const char* docstring, const PyVar* userdata);
+void py_new_function(py_Ref, py_CFunction, const char* sig, BindType bt);
+void py_new_function2(py_Ref, py_CFunction, const char* sig, BindType bt, const char* docstring, const py_Ref userdata);
 // old style argc-based function
-void py_new_nativefunc(PyVar*, py_CFunction, int argc, BindType bt);
-void py_new_nativefunc2(PyVar*, py_CFunction, int argc, BindType bt, const char* docstring, const PyVar* userdata);
+void py_new_nativefunc(py_Ref, py_CFunction, int argc, BindType bt);
+void py_new_nativefunc2(py_Ref, py_CFunction, int argc, BindType bt, const char* docstring, const py_Ref userdata);
 
-int py_setattr(PyVar* self, StrName name, const PyVar* val);
 
-PyVar py_new_module(const char* name);
-PyVar pk_new_module(const char* name, const char* package);
-
-// Type pk_new_type
+py_Ref py_new_module(const char* name);
+const py_Ref py_import(const char* name);
 
 #define py_isnull(self) ((self)->type == 0)
 
+
+/// Sets the name of the object to the given value.
+void py_setdict(py_Ref self, py_Name name, const py_Ref val);
+/// Returns a reference to the name of the object.
+py_Ref py_getdict(const py_Ref self, py_Name name);
+
+/// Sets the i-th slot of the object to the given value.
+void py_setslot(py_Ref self, int i, const py_Ref val);
+/// Returns a reference to the i-th slot of the object.
+py_Ref py_getslot(const py_Ref self, int i);
+
+/// Sets the attribute of the object to the given value.
+/// This is equivalent to `self.name = val`.
+/// Returns 0 | err
+int py_setattr(py_Ref self, py_Name name, const py_Ref val);
+
+/// Gets the attribute of the object.
+/// This is equivalent to `self.name`.
+/// Returns 0 | err
+int py_getattr(const py_Ref self, py_Name name, py_Ref out);
+
+void py_pushref(const py_Ref src);
+void py_copyref(const py_Ref src, py_Ref dst);
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/src/interpreter/frame.c b/src/interpreter/frame.c
index 3521b97c..36e6b3bd 100644
--- a/src/interpreter/frame.c
+++ b/src/interpreter/frame.c
@@ -10,7 +10,7 @@ void ValueStack__clear(ValueStack* self) {
     self->sp = self->begin;
 }
 
-PyVar* FastLocals__try_get_by_name(PyVar* locals, const CodeObject* co, StrName name){
+PyVar* FastLocals__try_get_by_name(PyVar* locals, const CodeObject* co, py_Name name){
     int index = c11_smallmap_n2i__get(&co->varnames_inv, name, -1);
     if(index == -1) return NULL;
     return &locals[index];
@@ -39,14 +39,14 @@ void UnwindTarget__delete(UnwindTarget* self){
     free(self);
 }
 
-Frame* Frame__new(const CodeObject* co, PyObject* module, PyObject* function, PyVar* p0, PyVar* locals, const CodeObject* locals_co){
+Frame* Frame__new(const CodeObject* co, const PyVar* module, const PyVar* function, PyVar* p0, PyVar* locals, const CodeObject* locals_co){
     static_assert(sizeof(Frame) <= kPoolFrameBlockSize, "!(sizeof(Frame) <= kPoolFrameBlockSize)");
     Frame* self = PoolFrame_alloc();
     self->f_back = NULL;
     self->ip = (Bytecode*)co->codes.data - 1;
     self->co = co;
-    self->module = module;
-    self->function = function;
+    self->module = module->_obj;
+    self->function = function->_obj;
     self->p0 = p0;
     self->locals = locals;
     self->locals_co = locals_co;
diff --git a/src/interpreter/gc.c b/src/interpreter/gc.c
index a55dfc74..94f0d5c7 100644
--- a/src/interpreter/gc.c
+++ b/src/interpreter/gc.c
@@ -88,21 +88,23 @@ int pk_ManagedHeap__sweep(pk_ManagedHeap *self){
     return freed;
 }
 
-PyObject* pk_ManagedHeap__new(pk_ManagedHeap *self, Type type, int size){
-    PyObject* obj = PyObject__new(type, size);
+PyObject* pk_ManagedHeap__new(pk_ManagedHeap *self, Type type, int slots, int size){
+    PyObject* obj = PyObject__new(type, slots, size);
     c11_vector__push(PyObject*, &self->no_gc, obj);
     return obj;
 }
 
-PyObject* pk_ManagedHeap__gcnew(pk_ManagedHeap *self, Type type, int size){
-    PyObject* obj = PyObject__new(type, size);
+PyObject* pk_ManagedHeap__gcnew(pk_ManagedHeap *self, Type type, int slots, int size){
+    PyObject* obj = PyObject__new(type, slots, size);
     c11_vector__push(PyObject*, &self->gen, obj);
     self->gc_counter++;
     return obj;
 }
 
-PyObject* PyObject__new(Type type, int size){
+PyObject* PyObject__new(Type type, int slots, int size){
+    assert(slots >= 0 || slots == -1);
     PyObject* self;
+    size += PK_OBJ_HEADER_SIZE(slots);
     if(size <= kPoolObjectBlockSize){
         self = PoolObject_alloc();
         self->gc_is_large = false;
@@ -112,6 +114,6 @@ PyObject* PyObject__new(Type type, int size){
     }
     self->type = type;
     self->gc_marked = false;
-    self->dict = NULL;
+    self->slots = slots;
     return self;
 }
diff --git a/src/interpreter/vm.c b/src/interpreter/vm.c
index 29c4816c..7830329b 100644
--- a/src/interpreter/vm.c
+++ b/src/interpreter/vm.c
@@ -15,7 +15,7 @@ static void pk_default_stderr(const char* s){
     fflush(stderr);
 }
 
-void pk_TypeInfo__ctor(pk_TypeInfo *self, StrName name, Type base, PyObject* obj, const PyVar* module, bool subclass_enabled){
+void pk_TypeInfo__ctor(pk_TypeInfo *self, py_Name name, Type base, PyObject* obj, const PyVar* module, bool subclass_enabled){
     memset(self, 0, sizeof(pk_TypeInfo));
     
     self->name = name;
@@ -25,14 +25,14 @@ void pk_TypeInfo__ctor(pk_TypeInfo *self, StrName name, Type base, PyObject* obj
     self->module = module ? *module : PY_NULL;
     self->subclass_enabled = subclass_enabled;
 
-    c11_vector__ctor(&self->annotated_fields, sizeof(StrName));
+    c11_vector__ctor(&self->annotated_fields, sizeof(py_Name));
 }
 
 void pk_TypeInfo__dtor(pk_TypeInfo *self){
     c11_vector__dtor(&self->annotated_fields);
 }
 
-static int _hello(const PyVar* args, int argc){
+static int _hello(const py_Ref args, int argc){
     return 0;
 }
 
@@ -40,7 +40,7 @@ static void do_builtin_bindings(){
     pk_VM* vm = pk_current_vm;
 
     py_new_nativefunc(&vm->reg[0], _hello, 2, BindType_FUNCTION);
-    py_setattr(&vm->builtins, pk_StrName__map("hello"), &vm->reg[0]);
+    py_setdict(&vm->builtins, py_name("hello"), &vm->reg[0]);
 }
 
 void pk_VM__ctor(pk_VM* self){
@@ -69,19 +69,19 @@ void pk_VM__ctor(pk_VM* self){
     ValueStack__ctor(&self->stack);
 
     self->True = (PyVar){.type=tp_bool, .is_ptr=true, .extra=1,
-        ._obj=pk_ManagedHeap__gcnew(&self->heap, tp_bool, 1),
+        ._obj=pk_ManagedHeap__gcnew(&self->heap, tp_bool, 0, 1),
     };
     self->False = (PyVar){.type=tp_bool, .is_ptr=true, .extra=0,
-        ._obj=pk_ManagedHeap__gcnew(&self->heap, tp_bool, 1),
+        ._obj=pk_ManagedHeap__gcnew(&self->heap, tp_bool, 0, 1),
     };
     self->None = (PyVar){.type=tp_none_type, .is_ptr=true,
-        ._obj=pk_ManagedHeap__gcnew(&self->heap, tp_none_type, 1),
+        ._obj=pk_ManagedHeap__gcnew(&self->heap, tp_none_type, 0, 1),
     };
     self->NotImplemented = (PyVar){.type=tp_not_implemented_type, .is_ptr=true,
-        ._obj=pk_ManagedHeap__gcnew(&self->heap, tp_not_implemented_type, 1),
+        ._obj=pk_ManagedHeap__gcnew(&self->heap, tp_not_implemented_type, 0, 1),
     };
     self->Ellipsis = (PyVar){.type=tp_ellipsis, .is_ptr=true,
-        ._obj=pk_ManagedHeap__gcnew(&self->heap, tp_ellipsis, 1),
+        ._obj=pk_ManagedHeap__gcnew(&self->heap, tp_ellipsis, 0, 1),
     };
 
     /* Init Builtin Types */
@@ -132,7 +132,7 @@ void pk_VM__ctor(pk_VM* self){
     #undef validate
 
     self->StopIteration = c11__at(pk_TypeInfo, &self->types, tp_stop_iteration)->self;
-    self->builtins = py_new_module("builtins");
+    self->builtins = *py_new_module("builtins");
     
     /* Setup Public Builtin Types */
     Type public_types[] = {
@@ -147,13 +147,13 @@ void pk_VM__ctor(pk_VM* self){
     for(int i=0; i<PK_ARRAY_COUNT(public_types); i++){
         Type t = public_types[i];
         pk_TypeInfo* ti = c11__at(pk_TypeInfo, &self->types, t);
-        pk_NameDict__set(self->builtins._obj->dict, ti->name, ti->self);
+        py_setdict(&self->builtins, ti->name, &ti->self);
     }
-    pk_NameDict__set(self->builtins._obj->dict, pk_StrName__map("NotImplemented"), self->NotImplemented);
+    py_setdict(&self->builtins, py_name("NotImplemented"), &self->NotImplemented);
 
     /* Do Buildin Bindings*/
     do_builtin_bindings();
-    self->main = py_new_module("__main__");
+    self->main = *py_new_module("__main__");
 }
 
 void pk_VM__dtor(pk_VM* self){
@@ -186,17 +186,18 @@ pk_FrameResult pk_VM__run_top_frame(pk_VM* self){
 Type pk_VM__new_type(pk_VM* self, const char* name, Type base, const PyVar* module, bool subclass_enabled){
     Type type = self->types.count;
     pk_TypeInfo* ti = c11_vector__emplace(&self->types);
-    PyObject* typeobj = pk_ManagedHeap__gcnew(&self->heap, tp_type, PK_OBJ_SIZEOF(Type));
-    *PyObject__as(Type, typeobj) = type;
-    pk_TypeInfo__ctor(ti, pk_StrName__map(name), base, typeobj, module, subclass_enabled);
+    PyObject* typeobj = pk_ManagedHeap__gcnew(&self->heap, tp_type, 0, sizeof(Type));
+    Type* value = PyObject__value(typeobj);
+    *value = type;
+    pk_TypeInfo__ctor(ti, py_name(name), base, typeobj, module, subclass_enabled);
     return type;
 }
 
 /****************************************/
 void PyObject__delete(PyObject *self){
     pk_TypeInfo* ti = c11__getitem(pk_TypeInfo*, &pk_current_vm->types, self->type);
-    if(ti->dtor) ti->dtor(PyObject__value_ptr(self));
-    if(self->dict) pk_NameDict__delete(self->dict);
+    if(ti->dtor) ti->dtor(PyObject__value(self));
+    if(self->slots == -1) pk_NameDict__dtor(PyObject__dict(self));
     if(self->gc_is_large){
         free(self);
     }else{
diff --git a/src/objects/dict.c b/src/objects/dict.c
index 8dfe376b..9387361f 100644
--- a/src/objects/dict.c
+++ b/src/objects/dict.c
@@ -1,5 +1,6 @@
 #include "pocketpy/objects/dict.h"
 #include "pocketpy/common/utils.h"
+#include <stdint.h>
 #include <stdlib.h>
 #include <assert.h>
 #include <string.h>
@@ -113,14 +114,18 @@ static void pkpy_Dict__extendht(pkpy_Dict* self) {
         struct pkpy_DictEntry* entry = &c11__getitem(struct pkpy_DictEntry, &self->_entries, i);
         if(pkpy_Var__is_null(&entry->key)) continue;
 
-        int rhash = DICT_HASH_TRANS(py_hash(&entry->key));
+        int64_t out;
+        int err = py_hash(&entry->key, &out);
+        int rhash = DICT_HASH_TRANS(out);
         int h = pkpy_Dict__probe0(self, entry->key, rhash);
         pkpy_Dict__htset(self, h, i);
     }
 }
 
 bool pkpy_Dict__set(pkpy_Dict* self, PyVar key, PyVar val) {
-    int hash = DICT_HASH_TRANS(py_hash(&key));
+    int64_t out;
+    int err = py_hash(&key, &out);
+    int hash = DICT_HASH_TRANS(out);
     int h = pkpy_Dict__probe1(self, key, hash);
 
     int idx = pkpy_Dict__htget(self, h);
@@ -155,7 +160,9 @@ bool pkpy_Dict__set(pkpy_Dict* self, PyVar key, PyVar val) {
 }
 
 bool pkpy_Dict__contains(const pkpy_Dict* self, PyVar key) {
-    int hash = DICT_HASH_TRANS(py_hash(&key));
+    int64_t out;
+    int err = py_hash(&key, &out);
+    int hash = DICT_HASH_TRANS(out);
     int h = pkpy_Dict__probe1(self, key, hash);
 
     int idx = pkpy_Dict__htget(self, h);
@@ -187,7 +194,9 @@ static bool pkpy_Dict__refactor(pkpy_Dict* self) {
         struct pkpy_DictEntry* entry = &c11__getitem(struct pkpy_DictEntry, &self->_entries, i);
         if(pkpy_Var__is_null(&entry->key)) continue;
 
-        int rhash = DICT_HASH_TRANS(py_hash(&entry->key));
+        int64_t out;
+        py_hash(&entry->key, &out);
+        int rhash = DICT_HASH_TRANS(out);
         int h = pkpy_Dict__probe0(self, entry->key, rhash);
         pkpy_Dict__htset(self, h, i);
     }
@@ -195,7 +204,9 @@ static bool pkpy_Dict__refactor(pkpy_Dict* self) {
 }
 
 bool pkpy_Dict__del(pkpy_Dict* self, PyVar key) {
-    int hash = DICT_HASH_TRANS(py_hash(&key));
+    int64_t out;
+    int err = py_hash(&key, &out);
+    int hash = DICT_HASH_TRANS(out);
     int h = pkpy_Dict__probe1(self, key, hash);
     int idx = pkpy_Dict__htget(self, h), null = pkpy_Dict__idx_null(self);
     if(idx == null) return false;
@@ -208,7 +219,9 @@ bool pkpy_Dict__del(pkpy_Dict* self, PyVar key) {
 }
 
 const PyVar *pkpy_Dict__try_get(const pkpy_Dict* self, PyVar key) {
-    int hash = DICT_HASH_TRANS(py_hash(&key));
+    int64_t out;
+    int err = py_hash(&key, &out);
+    int hash = DICT_HASH_TRANS(out);
     int h = pkpy_Dict__probe1(self, key, hash);
     
     int idx = pkpy_Dict__htget(self, h);
diff --git a/src/objects/object.c b/src/objects/object.c
index c6e8f25e..c0dd2552 100644
--- a/src/objects/object.c
+++ b/src/objects/object.c
@@ -1,4 +1,6 @@
 #include "pocketpy/objects/object.h"
+#include "pocketpy/pocketpy.h"
+#include <assert.h>
 
 void PyVar__ctor3(PyVar* self, PyObject* existing){
     assert(existing);
@@ -6,3 +8,17 @@ void PyVar__ctor3(PyVar* self, PyObject* existing){
     self->is_ptr = true;
     self->_obj = existing;
 }
+
+void* PyObject__value(PyObject* self){
+    return (char*)self + PK_OBJ_HEADER_SIZE(self->slots);
+}
+
+pk_NameDict* PyObject__dict(PyObject* self){
+    assert(self->slots == -1);
+    return (pk_NameDict*)((char*)self + 8);
+}
+
+PyVar* PyObject__slots(PyObject* self){
+    assert(self->slots >= 0);
+    return (PyVar*)((char*)self + 8);
+}
\ No newline at end of file
diff --git a/src/pocketpy.c b/src/pocketpy.c
index afe4c94c..4803df38 100644
--- a/src/pocketpy.c
+++ b/src/pocketpy.c
@@ -14,12 +14,12 @@ void py_initialize(){
     pk_VM__ctor(&pk_default_vm);
 }
 
-py_Error* py_exec_simple(const char* source){
+int py_exec_simple(const char* source){
     CodeObject* co = NULL;
     pk_VM* vm = pk_current_vm;
     Frame* frame = Frame__new(
         co,
-        vm->main,
+        &vm->main,
         NULL,
         vm->stack.sp,
         vm->stack.sp,
@@ -27,11 +27,19 @@ py_Error* py_exec_simple(const char* source){
     );
     pk_VM__push_frame(vm, frame);
     pk_FrameResult res = pk_VM__run_top_frame(vm);
-    if(res == RES_ERROR) return vm->last_error;
-    if(res == RES_RETURN) return NULL; // vm->last_retval;
+    if(res == RES_ERROR) return vm->last_error->type;
+    if(res == RES_RETURN) return 0; // vm->last_retval;
     assert(0);  // unreachable
 }
 
+py_Error* py_getlasterror(){
+    return pk_current_vm->last_error;
+}
+
+void py_Error__print(py_Error* self){
+    abort();
+}
+
 void py_finalize(){
     pk_VM__dtor(&pk_default_vm);
     pk_current_vm = NULL;
@@ -39,31 +47,17 @@ void py_finalize(){
     Pools_finalize();
 }
 
-void py_newint(PyVar* self, int64_t val){
+void py_setdict(py_Ref self, py_Name name, const py_Ref val){
+    pk_NameDict__set(
+        PyObject__dict(self->_obj),
+        name,
+        *val
+    );
+}
+
+void py_newint(py_Ref self, int64_t val){
     self->type = tp_int;
     self->is_ptr = false;
     self->_i64 = val;
 }
 
-void py_newfloat(PyVar* self, double val){
-    self->type = tp_float;
-    self->is_ptr = false;
-    self->_f64 = val;
-}
-
-void py_newbool(PyVar* self, bool val){
-    // return a global singleton
-}
-
-void py_newnone(PyVar* self){
-    // return a heap object
-}
-
-void py_newstr(PyVar* self, const char* val){
-    // return a heap object
-}
-
-void py_newstr2(PyVar*, const char*, int);
-
-void py_newbytes(PyVar*, const uint8_t*, int);
-
diff --git a/src2/main.c b/src2/main.c
index c4f0e3c7..005fca28 100644
--- a/src2/main.c
+++ b/src2/main.c
@@ -1,6 +1,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include "pocketpy.h"
+#include "pocketpy/pocketpy.h"
 
 char* read_file(const char* path) {
     FILE* file = fopen(path, "r");
@@ -27,10 +28,9 @@ int main(int argc, char** argv) {
     char* source = read_file(argv[1]);
     py_initialize();
 
-    py_Error* err = py_exec_simple(source);
-    if(err){
+    if(py_exec_simple(source)){
+        py_Error* err = py_getlasterror();
         py_Error__print(err);
-        py_Error__delete(err);
     }
     
     py_finalize();