diff --git a/build_cpp.sh b/build_cpp.sh
index 3a241834..974a6df7 100644
--- a/build_cpp.sh
+++ b/build_cpp.sh
@@ -1 +1 @@
-g++ -o pocketpy src/main.cpp --std=c++17 -O2 -Wall -Wno-sign-compare -Wno-unused-variable -fno-rtti
\ No newline at end of file
+g++ -o pocketpy src/main.cpp -Wfatal-errors --std=c++17 -O2 -Wall -Wno-sign-compare -Wno-unused-variable -fno-rtti
\ No newline at end of file
diff --git a/src/ceval.h b/src/ceval.h
index 3167306b..9b50a9e8 100644
--- a/src/ceval.h
+++ b/src/ceval.h
@@ -18,12 +18,12 @@ PyVar VM::run_frame(Frame* frame){
         case OP_LOAD_CONST: frame->push(frame->co->consts[byte.arg]); continue;
         case OP_LOAD_FUNCTION: {
             const PyVar obj = frame->co->consts[byte.arg];
-            Function f = PyFunction_AS_C(obj);  // copy
+            Function f = py_cast_v<Function>(this, obj);  // copy
             f._module = frame->_module;
-            frame->push(PyFunction(f));
+            frame->push(py_object(this, f));
         } continue;
         case OP_SETUP_CLOSURE: {
-            Function& f = PyFunction_AS_C(frame->top());    // reference
+            Function& f = py_cast<Function>(this, frame->top());    // reference
             f._closure = frame->_locals;
         } continue;
         case OP_LOAD_NAME_REF: {
@@ -70,7 +70,7 @@ PyVar VM::run_frame(Frame* frame){
             continue;
         case OP_BUILD_TUPLE: {
             Args items = frame->pop_n_values_reversed(this, byte.arg);
-            frame->push(PyTuple(std::move(items)));
+            frame->push(py_object(this, std::move(items)));
         } continue;
         case OP_BUILD_TUPLE_REF: {
             Args items = frame->pop_n_reversed(byte.arg);
@@ -79,13 +79,13 @@ PyVar VM::run_frame(Frame* frame){
         case OP_BUILD_STRING: {
             Args items = frame->pop_n_values_reversed(this, byte.arg);
             StrStream ss;
-            for(int i=0; i<items.size(); i++) ss << PyStr_AS_C(asStr(items[i]));
-            frame->push(PyStr(ss.str()));
+            for(int i=0; i<items.size(); i++) ss << py_cast<Str>(this, asStr(items[i]));
+            frame->push(py_object(this, ss.str()));
         } continue;
         case OP_LOAD_EVAL_FN: frame->push(builtins->attr(m_eval)); continue;
         case OP_LIST_APPEND: {
             PyVar obj = frame->pop_value(this);
-            List& list = PyList_AS_C(frame->top_1());
+            List& list = py_cast<List>(this, frame->top_1());
             list.push_back(std::move(obj));
         } continue;
         case OP_BEGIN_CLASS: {
@@ -109,7 +109,7 @@ PyVar VM::run_frame(Frame* frame){
         case OP_RETURN_VALUE: return frame->pop_value(this);
         case OP_PRINT_EXPR: {
             const PyVar expr = frame->top_value(this);
-            if(expr != None) *_stdout << PyStr_AS_C(asRepr(expr)) << '\n';
+            if(expr != None) *_stdout << py_cast<Str>(this, asRepr(expr)) << '\n';
         } continue;
         case OP_POP_TOP: frame->_pop(); continue;
         case OP_BINARY_OP: {
@@ -175,7 +175,7 @@ PyVar VM::run_frame(Frame* frame){
         case OP_LOAD_ELLIPSIS: frame->push(Ellipsis); continue;
         case OP_ASSERT: {
             PyVar _msg = frame->pop_value(this);
-            Str msg = PyStr_AS_C(asStr(_msg));
+            Str msg = py_cast<Str>(this, asStr(_msg));
             PyVar expr = frame->pop_value(this);
             if(asBool(expr) != True) _error("AssertionError", msg);
         } continue;
@@ -186,13 +186,13 @@ PyVar VM::run_frame(Frame* frame){
         } continue;
         case OP_RAISE: {
             PyVar obj = frame->pop_value(this);
-            Str msg = obj == None ? "" : PyStr_AS_C(asStr(obj));
+            Str msg = obj == None ? "" : py_cast<Str>(this, asStr(obj));
             StrName type = frame->co->names[byte.arg].first;
             _error(type, msg);
         } continue;
         case OP_RE_RAISE: _raise(); continue;
         case OP_BUILD_LIST:
-            frame->push(PyList(frame->pop_n_values_reversed(this, byte.arg).move_to_list()));
+            frame->push(py_object(this, frame->pop_n_values_reversed(this, byte.arg).move_to_list()));
             continue;
         case OP_BUILD_MAP: {
             Args items = frame->pop_n_values_reversed(this, byte.arg*2);
@@ -203,7 +203,7 @@ PyVar VM::run_frame(Frame* frame){
             frame->push(obj);
         } continue;
         case OP_BUILD_SET: {
-            PyVar list = PyList(
+            PyVar list = py_object(this, 
                 frame->pop_n_values_reversed(this, byte.arg).move_to_list()
             );
             PyVar obj = call(builtins->attr("set"), one_arg(list));
diff --git a/src/cffi.h b/src/cffi.h
index 6d3e2847..6d3ed055 100644
--- a/src/cffi.h
+++ b/src/cffi.h
@@ -16,10 +16,10 @@ struct CType{
         vm->bind_static_method<-1>(type, "__new__", CPP_NOT_IMPLEMENTED());
 
         vm->bind_method<0>(type, "__repr__", [](VM* vm, Args& args) {
-            CType& self = vm->py_cast<CType>(args[0]);
+            CType& self = vm->_cast<CType>(args[0]);
             StrStream ss;
             ss << "<c._type '" << self.name << "' (" << self.size*8 << " bits)>";
-            return vm->PyStr(ss.str());
+            return py_object(vm, ss.str());
         });
     }
 };
@@ -70,61 +70,61 @@ struct Pointer{
         vm->bind_static_method<-1>(type, "__new__", CPP_NOT_IMPLEMENTED());
 
         vm->bind_method<0>(type, "__repr__", [](VM* vm, Args& args) {
-            Pointer& self = vm->py_cast<Pointer>(args[0]);
+            Pointer& self = vm->_cast<Pointer>(args[0]);
             StrStream ss;
             ss << "<" << self.ctype.name << "* at " << (i64)self.ptr << ">";
-            return vm->PyStr(ss.str());
+            return py_object(vm, ss.str());
         });
 
         vm->bind_method<1>(type, "__add__", [](VM* vm, Args& args) {
-            Pointer& self = vm->py_cast<Pointer>(args[0]);
+            Pointer& self = vm->_cast<Pointer>(args[0]);
             return vm->new_object<Pointer>(self + py_cast<i64>(vm, args[1]));
         });
 
         vm->bind_method<1>(type, "__sub__", [](VM* vm, Args& args) {
-            Pointer& self = vm->py_cast<Pointer>(args[0]);
+            Pointer& self = vm->_cast<Pointer>(args[0]);
             return vm->new_object<Pointer>(self - py_cast_v<i64>(vm, args[1]));
         });
 
         vm->bind_method<1>(type, "__eq__", [](VM* vm, Args& args) {
-            Pointer& self = vm->py_cast<Pointer>(args[0]);
-            Pointer& other = vm->py_cast<Pointer>(args[1]);
+            Pointer& self = vm->_cast<Pointer>(args[0]);
+            Pointer& other = vm->_cast<Pointer>(args[1]);
             return vm->PyBool(self.ptr == other.ptr);
         });
 
         vm->bind_method<1>(type, "__ne__", [](VM* vm, Args& args) {
-            Pointer& self = vm->py_cast<Pointer>(args[0]);
-            Pointer& other = vm->py_cast<Pointer>(args[1]);
+            Pointer& self = vm->_cast<Pointer>(args[0]);
+            Pointer& other = vm->_cast<Pointer>(args[1]);
             return vm->PyBool(self.ptr != other.ptr);
         });
 
         // https://docs.python.org/zh-cn/3/library/ctypes.html
         vm->bind_method<1>(type, "__getitem__", [](VM* vm, Args& args) {
-            Pointer& self = vm->py_cast<Pointer>(args[0]);
+            Pointer& self = vm->_cast<Pointer>(args[0]);
             i64 index = py_cast_v<i64>(vm, args[1]);
             return (self+index).get(vm);
         });
 
         vm->bind_method<2>(type, "__setitem__", [](VM* vm, Args& args) {
-            Pointer& self = vm->py_cast<Pointer>(args[0]);
+            Pointer& self = vm->_cast<Pointer>(args[0]);
             i64 index = py_cast_v<i64>(vm, args[1]);
             (self+index).set(vm, args[2]);
             return vm->None;
         });
 
         vm->bind_method<1>(type, "cast", [](VM* vm, Args& args) {
-            Pointer& self = vm->py_cast<Pointer>(args[0]);
-            CType& ctype = vm->py_cast<CType>(args[1]);
+            Pointer& self = vm->_cast<Pointer>(args[0]);
+            CType& ctype = vm->_cast<CType>(args[1]);
             return vm->new_object<Pointer>(self.ptr, ctype);
         });
 
         vm->bind_method<0>(type, "get", [](VM* vm, Args& args) {
-            Pointer& self = vm->py_cast<Pointer>(args[0]);
+            Pointer& self = vm->_cast<Pointer>(args[0]);
             return self.get(vm);
         });
 
         vm->bind_method<1>(type, "set", [](VM* vm, Args& args) {
-            Pointer& self = vm->py_cast<Pointer>(args[0]);
+            Pointer& self = vm->_cast<Pointer>(args[0]);
             self.set(vm, args[1]);
             return vm->None;
         });
@@ -178,7 +178,7 @@ struct Pointer{
             case C_TYPE("uint16_"): ref<uint16_t>() = py_cast_v<i64>(vm, val); break;
             case C_TYPE("uint32_"): ref<uint32_t>() = py_cast_v<i64>(vm, val); break;
             case C_TYPE("uint64_"): ref<uint64_t>() = py_cast_v<i64>(vm, val); break;
-            case C_TYPE("void_p_"): ref<void*>() = vm->py_cast<Pointer>(val).ptr; break;
+            case C_TYPE("void_p_"): ref<void*>() = vm->_cast<Pointer>(val).ptr; break;
             // use macro here to do extension
             default: UNREACHABLE();
         }
@@ -242,10 +242,10 @@ struct Struct {
         });
 
         vm->bind_method<0>(type, "__repr__", [](VM* vm, Args& args) {
-            Struct& self = vm->py_cast<Struct>(args[0]);
+            Struct& self = vm->_cast<Struct>(args[0]);
             StrStream ss;
             ss << self.info->name << "(" << ")";
-            return vm->PyStr(ss.str());
+            return py_object(vm, ss.str());
         });
     }
 };
@@ -267,26 +267,26 @@ void add_module_c(VM* vm){
     });
 
     vm->bind_func<1>(mod, "free", [](VM* vm, Args& args) {
-        Pointer& self = vm->py_cast<Pointer>(args[0]);
+        Pointer& self = vm->_cast<Pointer>(args[0]);
         free(self.ptr);
         return vm->None;
     });
 
     vm->bind_func<1>(mod, "sizeof", [](VM* vm, Args& args) {
-        CType& ctype = vm->py_cast<CType>(args[0]);
+        CType& ctype = vm->_cast<CType>(args[0]);
         return py_object(vm, ctype.size);
     });
 
     vm->bind_func<3>(mod, "memcpy", [](VM* vm, Args& args) {
-        Pointer& dst = vm->py_cast<Pointer>(args[0]);
-        Pointer& src = vm->py_cast<Pointer>(args[1]);
+        Pointer& dst = vm->_cast<Pointer>(args[0]);
+        Pointer& src = vm->_cast<Pointer>(args[1]);
         i64 size = py_cast_v<i64>(vm, args[2]);
         memcpy(dst.ptr, src.ptr, size);
         return vm->None;
     });
 
     vm->bind_func<3>(mod, "memset", [](VM* vm, Args& args) {
-        Pointer& dst = vm->py_cast<Pointer>(args[0]);
+        Pointer& dst = vm->_cast<Pointer>(args[0]);
         i64 val = py_cast_v<i64>(vm, args[1]);
         i64 size = py_cast_v<i64>(vm, args[2]);
         memset(dst.ptr, (int)val, size);
@@ -295,10 +295,10 @@ void add_module_c(VM* vm){
 
     vm->bind_func<1>(mod, "strdup", [ptr_t](VM* vm, Args& args) {
         if(is_type(args[0], vm->tp_str)){
-            const Str& s = vm->PyStr_AS_C(args[0]);
+            const Str& s = py_cast<Str>(vm, args[0]);
             return vm->new_object<Pointer>(strdup(s.c_str()), C_TYPE_T("char_"));
         }else if(is_type(args[0], OBJ_GET(Type, ptr_t))){
-            Pointer& p = vm->py_cast<Pointer>(args[0]);
+            Pointer& p = vm->_cast<Pointer>(args[0]);
             return vm->new_object<Pointer>(strdup(p.cast<char*>()), C_TYPE_T("char_"));
         }else{
             vm->TypeError("strdup() argument must be 'str' or 'char*'");
@@ -307,13 +307,13 @@ void add_module_c(VM* vm){
     });
 
     vm->bind_func<2>(mod, "strcmp", [](VM* vm, Args& args) {
-        Pointer& p1 = vm->py_cast<Pointer>(args[0]);
-        Pointer& p2 = vm->py_cast<Pointer>(args[1]);
+        Pointer& p1 = vm->_cast<Pointer>(args[0]);
+        Pointer& p2 = vm->_cast<Pointer>(args[1]);
         return py_object(vm, strcmp(p1.cast<char*>(), p2.cast<char*>()));
     });
 
     vm->bind_func<1>(mod, "strlen", [](VM* vm, Args& args) {
-        Pointer& p = vm->py_cast<Pointer>(args[0]);
+        Pointer& p = vm->_cast<Pointer>(args[0]);
         return py_object(vm, strlen(p.cast<char*>()));
     });
 }
diff --git a/src/compiler.h b/src/compiler.h
index ec0ac260..6a8436c5 100644
--- a/src/compiler.h
+++ b/src/compiler.h
@@ -147,9 +147,9 @@ private:
     void eat_string(char quote, StringType type) {
         Str s = eat_string_until(quote, type == RAW_STRING);
         if(type == F_STRING){
-            parser->set_next_token(TK("@fstr"), vm->PyStr(s));
+            parser->set_next_token(TK("@fstr"), py_object(vm, s));
         }else{
-            parser->set_next_token(TK("@str"), vm->PyStr(s));
+            parser->set_next_token(TK("@str"), py_object(vm, s));
         }
     }
 
@@ -360,7 +360,7 @@ private:
     void exprFString() {
         static const std::regex pattern(R"(\{(.*?)\})");
         PyVar value = parser->prev.value;
-        Str s = vm->PyStr_AS_C(value);
+        Str s = py_cast<Str>(vm, value);
         std::sregex_iterator begin(s.begin(), s.end(), pattern);
         std::sregex_iterator end;
         int size = 0;
@@ -369,18 +369,18 @@ private:
             std::smatch m = *it;
             if (i < m.position()) {
                 std::string literal = s.substr(i, m.position() - i);
-                emit(OP_LOAD_CONST, co()->add_const(vm->PyStr(literal)));
+                emit(OP_LOAD_CONST, co()->add_const(py_object(vm, literal)));
                 size++;
             }
             emit(OP_LOAD_EVAL_FN);
-            emit(OP_LOAD_CONST, co()->add_const(vm->PyStr(m[1].str())));
+            emit(OP_LOAD_CONST, co()->add_const(py_object(vm, m[1].str())));
             emit(OP_CALL, 1);
             size++;
             i = (int)(m.position() + m.length());
         }
         if (i < s.size()) {
             std::string literal = s.substr(i, s.size() - i);
-            emit(OP_LOAD_CONST, co()->add_const(vm->PyStr(literal)));
+            emit(OP_LOAD_CONST, co()->add_const(py_object(vm, literal)));
             size++;
         }
         emit(OP_BUILD_STRING, size);
@@ -399,7 +399,7 @@ private:
         emit(OP_RETURN_VALUE);
         func.code->optimize(vm);
         this->codes.pop();
-        emit(OP_LOAD_FUNCTION, co()->add_const(vm->PyFunction(func)));
+        emit(OP_LOAD_FUNCTION, co()->add_const(py_object(vm, func)));
         if(name_scope() == NAME_LOCAL) emit(OP_SETUP_CLOSURE);
     }
 
@@ -613,7 +613,7 @@ __LISTCOMP:
             if(peek() == TK("@id") && peek_next() == TK("=")) {
                 consume(TK("@id"));
                 const Str& key = parser->prev.str();
-                emit(OP_LOAD_CONST, co()->add_const(vm->PyStr(key)));
+                emit(OP_LOAD_CONST, co()->add_const(py_object(vm, key)));
                 consume(TK("="));
                 co()->_rvalue += 1; EXPR(); co()->_rvalue -= 1;
                 KWARGC++;
@@ -929,7 +929,7 @@ __LISTCOMP:
             co()->_rvalue += 1;
             EXPR();
             if (match(TK(","))) EXPR();
-            else emit(OP_LOAD_CONST, co()->add_const(vm->PyStr("")));
+            else emit(OP_LOAD_CONST, co()->add_const(py_object(vm, "")));
             co()->_rvalue -= 1;
             emit(OP_ASSERT);
             consume_end_stmt();
@@ -1073,7 +1073,7 @@ __LISTCOMP:
         compile_block_body();
         func.code->optimize(vm);
         this->codes.pop();
-        emit(OP_LOAD_FUNCTION, co()->add_const(vm->PyFunction(func)));
+        emit(OP_LOAD_FUNCTION, co()->add_const(py_object(vm, func)));
         if(name_scope() == NAME_LOCAL) emit(OP_SETUP_CLOSURE);
         if(!co()->_is_compiling_class){
             if(obj_name.empty()){
diff --git a/src/iter.h b/src/iter.h
index 21580ff8..547c522f 100644
--- a/src/iter.h
+++ b/src/iter.h
@@ -46,7 +46,7 @@ public:
 
     PyVar next() {
         if(index == str->u8_length()) return nullptr;
-        return vm->PyStr(str->u8_getitem(index++));
+        return py_object(vm, str->u8_getitem(index++));
     }
 };
 
diff --git a/src/main.cpp b/src/main.cpp
index 5d143a69..4d9dfb56 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -8,7 +8,7 @@ int main(int argc, char** argv){
     vm->bind_builtin_func<0>("input", [](pkpy::VM* vm, pkpy::Args& args){
         static std::string line;
         std::getline(std::cin, line);
-        return vm->PyStr(line);
+        return py_object(vm, line);
     });
     if(argc == 1){
         pkpy::REPL* repl = pkpy_new_repl(vm);
diff --git a/src/pocketpy.h b/src/pocketpy.h
index 1a6d92c2..d8d8d795 100644
--- a/src/pocketpy.h
+++ b/src/pocketpy.h
@@ -56,7 +56,7 @@ void init_builtins(VM* _vm) {
 #undef BIND_NUM_LOGICAL_OPT
 
     _vm->bind_builtin_func<1>("__sys_stdout_write", [](VM* vm, Args& args) {
-        (*vm->_stdout) << vm->PyStr_AS_C(args[0]);
+        (*vm->_stdout) << py_cast<Str>(vm, args[0]);
         return vm->None;
     });
 
@@ -78,12 +78,12 @@ void init_builtins(VM* _vm) {
     });
 
     _vm->bind_builtin_func<1>("eval", [](VM* vm, Args& args) {
-        CodeObject_ code = vm->compile(vm->PyStr_AS_C(args[0]), "<eval>", EVAL_MODE);
+        CodeObject_ code = vm->compile(py_cast<Str>(vm, args[0]), "<eval>", EVAL_MODE);
         return vm->_exec(code, vm->top_frame()->_module, vm->top_frame()->_locals);
     });
 
     _vm->bind_builtin_func<1>("exec", [](VM* vm, Args& args) {
-        CodeObject_ code = vm->compile(vm->PyStr_AS_C(args[0]), "<exec>", EXEC_MODE);
+        CodeObject_ code = vm->compile(py_cast<Str>(vm, args[0]), "<exec>", EXEC_MODE);
         vm->_exec(code, vm->top_frame()->_module, vm->top_frame()->_locals);
         return vm->None;
     });
@@ -107,33 +107,33 @@ void init_builtins(VM* _vm) {
     _vm->bind_builtin_func<1>("chr", [](VM* vm, Args& args) {
         i64 i = py_cast_v<i64>(vm, args[0]);
         if (i < 0 || i > 128) vm->ValueError("chr() arg not in range(128)");
-        return vm->PyStr(std::string(1, (char)i));
+        return py_object(vm, std::string(1, (char)i));
     });
 
     _vm->bind_builtin_func<1>("ord", [](VM* vm, Args& args) {
-        Str s = vm->PyStr_AS_C(args[0]);
+        Str s = py_cast<Str>(vm, args[0]);
         if (s.size() != 1) vm->TypeError("ord() expected an ASCII character");
         return py_object(vm, (i64)(s.c_str()[0]));
     });
 
     _vm->bind_builtin_func<2>("hasattr", [](VM* vm, Args& args) {
-        return vm->PyBool(vm->getattr(args[0], vm->PyStr_AS_C(args[1]), false) != nullptr);
+        return vm->PyBool(vm->getattr(args[0], py_cast<Str>(vm, args[1]), false) != nullptr);
     });
 
     _vm->bind_builtin_func<3>("setattr", [](VM* vm, Args& args) {
-        vm->setattr(args[0], vm->PyStr_AS_C(args[1]), args[2]);
+        vm->setattr(args[0], py_cast<Str>(vm, args[1]), args[2]);
         return vm->None;
     });
 
     _vm->bind_builtin_func<2>("getattr", [](VM* vm, Args& args) {
-        Str name = vm->PyStr_AS_C(args[1]);
+        Str name = py_cast<Str>(vm, args[1]);
         return vm->getattr(args[0], name);
     });
 
     _vm->bind_builtin_func<1>("hex", [](VM* vm, Args& args) {
         std::stringstream ss;
         ss << std::hex << py_cast_v<i64>(vm, args[0]);
-        return vm->PyStr("0x" + ss.str());
+        return py_object(vm, "0x" + ss.str());
     });
 
     _vm->bind_builtin_func<1>("dir", [](VM* vm, Args& args) {
@@ -146,8 +146,8 @@ void init_builtins(VM* _vm) {
         std::vector<StrName> keys = t_attr.keys();
         names.insert(keys.begin(), keys.end());
         List ret;
-        for (StrName name : names) ret.push_back(vm->PyStr(name.str()));
-        return vm->PyList(std::move(ret));
+        for (StrName name : names) ret.push_back(py_object(vm, name.str()));
+        return py_object(vm, std::move(ret));
     });
 
     _vm->bind_method<0>("object", "__repr__", [](VM* vm, Args& args) {
@@ -156,7 +156,7 @@ void init_builtins(VM* _vm) {
         StrStream ss;
         ss << std::hex << addr;
         Str s = "<" + OBJ_NAME(vm->_t(self)) + " object at 0x" + ss.str() + ">";
-        return vm->PyStr(s);
+        return py_object(vm, s);
     });
 
     _vm->bind_method<1>("object", "__eq__", CPP_LAMBDA(vm->PyBool(args[0] == args[1])));
@@ -179,8 +179,8 @@ void init_builtins(VM* _vm) {
         vm->PyIter(RangeIter(vm, args[0]))
     ));
 
-    _vm->bind_method<0>("NoneType", "__repr__", CPP_LAMBDA(vm->PyStr("None")));
-    _vm->bind_method<0>("NoneType", "__json__", CPP_LAMBDA(vm->PyStr("null")));
+    _vm->bind_method<0>("NoneType", "__repr__", CPP_LAMBDA(py_object(vm, "None")));
+    _vm->bind_method<0>("NoneType", "__json__", CPP_LAMBDA(py_object(vm, "null")));
 
     _vm->_bind_methods<1>({"int", "float"}, "__truediv__", [](VM* vm, Args& args) {
         f64 rhs = vm->num_to_float(args[1]);
@@ -213,7 +213,7 @@ void init_builtins(VM* _vm) {
         if (is_type(args[0], vm->tp_float)) return py_object(vm, (i64)py_cast_v<f64>(vm, args[0]));
         if (is_type(args[0], vm->tp_bool)) return py_object(vm, vm->_PyBool_AS_C(args[0]) ? 1 : 0);
         if (is_type(args[0], vm->tp_str)) {
-            const Str& s = vm->PyStr_AS_C(args[0]);
+            const Str& s = py_cast<Str>(vm, args[0]);
             try{
                 size_t parsed = 0;
                 i64 val = S_TO_INT(s, &parsed, 10);
@@ -239,8 +239,8 @@ void init_builtins(VM* _vm) {
         return py_object(vm, py_cast_v<i64>(vm, args[0]) % rhs);
     });
 
-    _vm->bind_method<0>("int", "__repr__", CPP_LAMBDA(vm->PyStr(std::to_string(py_cast_v<i64>(vm, args[0])))));
-    _vm->bind_method<0>("int", "__json__", CPP_LAMBDA(vm->PyStr(std::to_string(py_cast_v<i64>(vm, args[0])))));
+    _vm->bind_method<0>("int", "__repr__", CPP_LAMBDA(py_object(vm, std::to_string(py_cast_v<i64>(vm, args[0])))));
+    _vm->bind_method<0>("int", "__json__", CPP_LAMBDA(py_object(vm, std::to_string(py_cast_v<i64>(vm, args[0])))));
 
 #define INT_BITWISE_OP(name,op) \
     _vm->bind_method<1>("int", #name, CPP_LAMBDA(py_object(vm, py_cast_v<i64>(vm, args[0]) op py_cast_v<i64>(vm, args[1]))));
@@ -259,7 +259,7 @@ void init_builtins(VM* _vm) {
         if (is_type(args[0], vm->tp_float)) return args[0];
         if (is_type(args[0], vm->tp_bool)) return py_object(vm, vm->_PyBool_AS_C(args[0]) ? 1.0 : 0.0);
         if (is_type(args[0], vm->tp_str)) {
-            const Str& s = vm->PyStr_AS_C(args[0]);
+            const Str& s = py_cast<Str>(vm, args[0]);
             if(s == "inf") return py_object(vm, INFINITY);
             if(s == "-inf") return py_object(vm, -INFINITY);
             try{
@@ -275,37 +275,37 @@ void init_builtins(VM* _vm) {
 
     _vm->bind_method<0>("float", "__repr__", [](VM* vm, Args& args) {
         f64 val = py_cast_v<f64>(vm, args[0]);
-        if(std::isinf(val) || std::isnan(val)) return vm->PyStr(std::to_string(val));
+        if(std::isinf(val) || std::isnan(val)) return py_object(vm, std::to_string(val));
         StrStream ss;
         ss << std::setprecision(std::numeric_limits<f64>::max_digits10-1-2) << val;
         std::string s = ss.str();
         if(std::all_of(s.begin()+1, s.end(), isdigit)) s += ".0";
-        return vm->PyStr(s);
+        return py_object(vm, s);
     });
 
     _vm->bind_method<0>("float", "__json__", [](VM* vm, Args& args) {
         f64 val = py_cast_v<f64>(vm, args[0]);
         if(std::isinf(val) || std::isnan(val)) vm->ValueError("cannot jsonify 'nan' or 'inf'");
-        return vm->PyStr(std::to_string(val));
+        return py_object(vm, std::to_string(val));
     });
 
     /************ PyString ************/
     _vm->bind_static_method<1>("str", "__new__", CPP_LAMBDA(vm->asStr(args[0])));
 
     _vm->bind_method<1>("str", "__add__", [](VM* vm, Args& args) {
-        const Str& lhs = vm->PyStr_AS_C(args[0]);
-        const Str& rhs = vm->PyStr_AS_C(args[1]);
-        return vm->PyStr(lhs + rhs);
+        const Str& lhs = py_cast<Str>(vm, args[0]);
+        const Str& rhs = py_cast<Str>(vm, args[1]);
+        return py_object(vm, lhs + rhs);
     });
 
     _vm->bind_method<0>("str", "__len__", [](VM* vm, Args& args) {
-        const Str& self = vm->PyStr_AS_C(args[0]);
+        const Str& self = py_cast<Str>(vm, args[0]);
         return py_object(vm, self.u8_length());
     });
 
     _vm->bind_method<1>("str", "__contains__", [](VM* vm, Args& args) {
-        const Str& self = vm->PyStr_AS_C(args[0]);
-        const Str& other = vm->PyStr_AS_C(args[1]);
+        const Str& self = py_cast<Str>(vm, args[0]);
+        const Str& other = py_cast<Str>(vm, args[1]);
         return vm->PyBool(self.find(other) != Str::npos);
     });
 
@@ -313,57 +313,57 @@ void init_builtins(VM* _vm) {
     _vm->bind_method<0>("str", "__iter__", CPP_LAMBDA(vm->PyIter(StringIter(vm, args[0]))));
 
     _vm->bind_method<0>("str", "__repr__", [](VM* vm, Args& args) {
-        const Str& _self = vm->PyStr_AS_C(args[0]);
-        return vm->PyStr(_self.escape(true));
+        const Str& _self = py_cast<Str>(vm, args[0]);
+        return py_object(vm, _self.escape(true));
     });
 
     _vm->bind_method<0>("str", "__json__", [](VM* vm, Args& args) {
-        const Str& _self = vm->PyStr_AS_C(args[0]);
-        return vm->PyStr(_self.escape(false));
+        const Str& _self = py_cast<Str>(vm, args[0]);
+        return py_object(vm, _self.escape(false));
     });
 
     _vm->bind_method<1>("str", "__eq__", [](VM* vm, Args& args) {
         if(is_type(args[0], vm->tp_str) && is_type(args[1], vm->tp_str))
-            return vm->PyBool(vm->PyStr_AS_C(args[0]) == vm->PyStr_AS_C(args[1]));
+            return vm->PyBool(py_cast<Str>(vm, args[0]) == py_cast<Str>(vm, args[1]));
         return vm->PyBool(args[0] == args[1]);
     });
 
     _vm->bind_method<1>("str", "__ne__", [](VM* vm, Args& args) {
         if(is_type(args[0], vm->tp_str) && is_type(args[1], vm->tp_str))
-            return vm->PyBool(vm->PyStr_AS_C(args[0]) != vm->PyStr_AS_C(args[1]));
+            return vm->PyBool(py_cast<Str>(vm, args[0]) != py_cast<Str>(vm, args[1]));
         return vm->PyBool(args[0] != args[1]);
     });
 
     _vm->bind_method<1>("str", "__getitem__", [](VM* vm, Args& args) {
-        const Str& self (vm->PyStr_AS_C(args[0]));
+        const Str& self (py_cast<Str>(vm, args[0]));
 
         if(is_type(args[1], vm->tp_slice)){
             Slice s = vm->PySlice_AS_C(args[1]);
             s.normalize(self.u8_length());
-            return vm->PyStr(self.u8_substr(s.start, s.stop));
+            return py_object(vm, self.u8_substr(s.start, s.stop));
         }
 
         int index = (int)py_cast_v<i64>(vm, args[1]);
         index = vm->normalized_index(index, self.u8_length());
-        return vm->PyStr(self.u8_getitem(index));
+        return py_object(vm, self.u8_getitem(index));
     });
 
     _vm->bind_method<1>("str", "__gt__", [](VM* vm, Args& args) {
-        const Str& self (vm->PyStr_AS_C(args[0]));
-        const Str& obj (vm->PyStr_AS_C(args[1]));
+        const Str& self (py_cast<Str>(vm, args[0]));
+        const Str& obj (py_cast<Str>(vm, args[1]));
         return vm->PyBool(self > obj);
     });
 
     _vm->bind_method<1>("str", "__lt__", [](VM* vm, Args& args) {
-        const Str& self (vm->PyStr_AS_C(args[0]));
-        const Str& obj (vm->PyStr_AS_C(args[1]));
+        const Str& self (py_cast<Str>(vm, args[0]));
+        const Str& obj (py_cast<Str>(vm, args[1]));
         return vm->PyBool(self < obj);
     });
 
     _vm->bind_method<2>("str", "replace", [](VM* vm, Args& args) {
-        const Str& _self = vm->PyStr_AS_C(args[0]);
-        const Str& _old = vm->PyStr_AS_C(args[1]);
-        const Str& _new = vm->PyStr_AS_C(args[2]);
+        const Str& _self = py_cast<Str>(vm, args[0]);
+        const Str& _old = py_cast<Str>(vm, args[1]);
+        const Str& _new = py_cast<Str>(vm, args[2]);
         Str _copy = _self;
         // replace all occurences of _old with _new in _copy
         size_t pos = 0;
@@ -371,82 +371,82 @@ void init_builtins(VM* _vm) {
             _copy.replace(pos, _old.length(), _new);
             pos += _new.length();
         }
-        return vm->PyStr(_copy);
+        return py_object(vm, _copy);
     });
 
     _vm->bind_method<1>("str", "startswith", [](VM* vm, Args& args) {
-        const Str& _self = vm->PyStr_AS_C(args[0]);
-        const Str& _prefix = vm->PyStr_AS_C(args[1]);
+        const Str& _self = py_cast<Str>(vm, args[0]);
+        const Str& _prefix = py_cast<Str>(vm, args[1]);
         return vm->PyBool(_self.find(_prefix) == 0);
     });
 
     _vm->bind_method<1>("str", "endswith", [](VM* vm, Args& args) {
-        const Str& _self = vm->PyStr_AS_C(args[0]);
-        const Str& _suffix = vm->PyStr_AS_C(args[1]);
+        const Str& _self = py_cast<Str>(vm, args[0]);
+        const Str& _suffix = py_cast<Str>(vm, args[1]);
         return vm->PyBool(_self.rfind(_suffix) == _self.length() - _suffix.length());
     });
 
     _vm->bind_method<1>("str", "join", [](VM* vm, Args& args) {
-        const Str& self = vm->PyStr_AS_C(args[0]);
+        const Str& self = py_cast<Str>(vm, args[0]);
         StrStream ss;
         PyVar obj = vm->asList(args[1]);
-        const List& list = vm->PyList_AS_C(obj);
+        const List& list = py_cast<List>(vm, obj);
         for (int i = 0; i < list.size(); ++i) {
             if (i > 0) ss << self;
-            ss << vm->PyStr_AS_C(list[i]);
+            ss << py_cast<Str>(vm, list[i]);
         }
-        return vm->PyStr(ss.str());
+        return py_object(vm, ss.str());
     });
 
     /************ PyList ************/
     _vm->bind_method<1>("list", "append", [](VM* vm, Args& args) {
-        List& self = vm->PyList_AS_C(args[0]);
+        List& self = py_cast<List>(vm, args[0]);
         self.push_back(args[1]);
         return vm->None;
     });
 
     _vm->bind_method<0>("list", "reverse", [](VM* vm, Args& args) {
-        List& self = vm->PyList_AS_C(args[0]);
+        List& self = py_cast<List>(vm, args[0]);
         std::reverse(self.begin(), self.end());
         return vm->None;
     });
 
     _vm->bind_method<1>("list", "__mul__", [](VM* vm, Args& args) {
-        const List& self = vm->PyList_AS_C(args[0]);
+        const List& self = py_cast<List>(vm, args[0]);
         int n = (int)py_cast_v<i64>(vm, args[1]);
         List result;
         result.reserve(self.size() * n);
         for(int i = 0; i < n; i++) result.insert(result.end(), self.begin(), self.end());
-        return vm->PyList(std::move(result));
+        return py_object(vm, std::move(result));
     });
 
     _vm->bind_method<2>("list", "insert", [](VM* vm, Args& args) {
-        List& _self = vm->PyList_AS_C(args[0]);
+        List& self = py_cast<List>(vm, args[0]);
         int index = (int)py_cast_v<i64>(vm, args[1]);
-        if(index < 0) index += _self.size();
+        if(index < 0) index += self.size();
         if(index < 0) index = 0;
-        if(index > _self.size()) index = _self.size();
-        _self.insert(_self.begin() + index, args[2]);
+        if(index > self.size()) index = self.size();
+        self.insert(self.begin() + index, args[2]);
         return vm->None;
     });
 
     _vm->bind_method<0>("list", "clear", [](VM* vm, Args& args) {
-        vm->PyList_AS_C(args[0]).clear();
+        py_cast<List>(vm, args[0]).clear();
         return vm->None;
     });
 
-    _vm->bind_method<0>("list", "copy", CPP_LAMBDA(vm->PyList(vm->PyList_AS_C(args[0]))));
+    _vm->bind_method<0>("list", "copy", CPP_LAMBDA(py_object(vm, py_cast<List>(vm, args[0]))));
 
     _vm->bind_method<1>("list", "__add__", [](VM* vm, Args& args) {
-        const List& self = vm->PyList_AS_C(args[0]);
-        const List& obj = vm->PyList_AS_C(args[1]);
+        const List& self = py_cast<List>(vm, args[0]);
+        const List& obj = py_cast<List>(vm, args[1]);
         List new_list = self;
         new_list.insert(new_list.end(), obj.begin(), obj.end());
-        return vm->PyList(new_list);
+        return py_object(vm, new_list);
     });
 
     _vm->bind_method<0>("list", "__len__", [](VM* vm, Args& args) {
-        const List& self = vm->PyList_AS_C(args[0]);
+        const List& self = py_cast<List>(vm, args[0]);
         return py_object(vm, self.size());
     });
 
@@ -455,14 +455,14 @@ void init_builtins(VM* _vm) {
     });
 
     _vm->bind_method<1>("list", "__getitem__", [](VM* vm, Args& args) {
-        const List& self = vm->PyList_AS_C(args[0]);
+        const List& self = py_cast<List>(vm, args[0]);
 
         if(is_type(args[1], vm->tp_slice)){
             Slice s = vm->PySlice_AS_C(args[1]);
             s.normalize(self.size());
             List new_list;
             for(size_t i = s.start; i < s.stop; i++) new_list.push_back(self[i]);
-            return vm->PyList(std::move(new_list));
+            return py_object(vm, std::move(new_list));
         }
 
         int index = (int)py_cast_v<i64>(vm, args[1]);
@@ -471,7 +471,7 @@ void init_builtins(VM* _vm) {
     });
 
     _vm->bind_method<2>("list", "__setitem__", [](VM* vm, Args& args) {
-        List& self = vm->PyList_AS_C(args[0]);
+        List& self = py_cast<List>(vm, args[0]);
         int index = (int)py_cast_v<i64>(vm, args[1]);
         index = vm->normalized_index(index, self.size());
         self[index] = args[2];
@@ -479,7 +479,7 @@ void init_builtins(VM* _vm) {
     });
 
     _vm->bind_method<1>("list", "__delitem__", [](VM* vm, Args& args) {
-        List& self = vm->PyList_AS_C(args[0]);
+        List& self = py_cast<List>(vm, args[0]);
         int index = (int)py_cast_v<i64>(vm, args[1]);
         index = vm->normalized_index(index, self.size());
         self.erase(self.begin() + index);
@@ -488,8 +488,8 @@ void init_builtins(VM* _vm) {
 
     /************ PyTuple ************/
     _vm->bind_static_method<1>("tuple", "__new__", [](VM* vm, Args& args) {
-        List list = vm->PyList_AS_C(vm->asList(args[0]));
-        return vm->PyTuple(std::move(list));
+        List list = py_cast<List>(vm, vm->asList(args[0]));
+        return py_object(vm, std::move(list));
     });
 
     _vm->bind_method<0>("tuple", "__iter__", [](VM* vm, Args& args) {
@@ -497,14 +497,14 @@ void init_builtins(VM* _vm) {
     });
 
     _vm->bind_method<1>("tuple", "__getitem__", [](VM* vm, Args& args) {
-        const Tuple& self = vm->PyTuple_AS_C(args[0]);
+        const Tuple& self = py_cast<Tuple>(vm, args[0]);
 
         if(is_type(args[1], vm->tp_slice)){
             Slice s = vm->PySlice_AS_C(args[1]);
             s.normalize(self.size());
             List new_list;
             for(size_t i = s.start; i < s.stop; i++) new_list.push_back(self[i]);
-            return vm->PyTuple(std::move(new_list));
+            return py_object(vm, std::move(new_list));
         }
 
         int index = (int)py_cast_v<i64>(vm, args[1]);
@@ -513,7 +513,7 @@ void init_builtins(VM* _vm) {
     });
 
     _vm->bind_method<0>("tuple", "__len__", [](VM* vm, Args& args) {
-        const Tuple& self = vm->PyTuple_AS_C(args[0]);
+        const Tuple& self = py_cast<Tuple>(vm, args[0]);
         return py_object(vm, self.size());
     });
 
@@ -522,12 +522,12 @@ void init_builtins(VM* _vm) {
 
     _vm->bind_method<0>("bool", "__repr__", [](VM* vm, Args& args) {
         bool val = vm->PyBool_AS_C(args[0]);
-        return vm->PyStr(val ? "True" : "False");
+        return py_object(vm, val ? "True" : "False");
     });
 
     _vm->bind_method<0>("bool", "__json__", [](VM* vm, Args& args) {
         bool val = vm->PyBool_AS_C(args[0]);
-        return vm->PyStr(val ? "true" : "false");
+        return py_object(vm, val ? "true" : "false");
     });
 
     _vm->bind_method<1>("bool", "__xor__", [](VM* vm, Args& args) {
@@ -536,7 +536,7 @@ void init_builtins(VM* _vm) {
         return vm->PyBool(self ^ other);
     });
 
-    _vm->bind_method<0>("ellipsis", "__repr__", CPP_LAMBDA(vm->PyStr("Ellipsis")));
+    _vm->bind_method<0>("ellipsis", "__repr__", CPP_LAMBDA(py_object(vm, "Ellipsis")));
 }
 
 #include "builtins.h"
@@ -563,7 +563,7 @@ void add_module_time(VM* vm){
 
 void add_module_sys(VM* vm){
     PyVar mod = vm->new_module("sys");
-    vm->setattr(mod, "version", vm->PyStr(PK_VERSION));
+    vm->setattr(mod, "version", py_object(vm, PK_VERSION));
 
     vm->bind_func<1>(mod, "getrefcount", CPP_LAMBDA(py_object(vm, args[0].use_count())));
     vm->bind_func<0>(mod, "getrecursionlimit", CPP_LAMBDA(py_object(vm, vm->recursionlimit)));
@@ -577,7 +577,7 @@ void add_module_sys(VM* vm){
 void add_module_json(VM* vm){
     PyVar mod = vm->new_module("json");
     vm->bind_func<1>(mod, "loads", [](VM* vm, Args& args) {
-        const Str& expr = vm->PyStr_AS_C(args[0]);
+        const Str& expr = py_cast<Str>(vm, args[0]);
         CodeObject_ code = vm->compile(expr, "<json>", JSON_MODE);
         return vm->_exec(code, vm->top_frame()->_module, vm->top_frame()->_locals);
     });
@@ -609,7 +609,7 @@ void add_module_dis(VM* vm){
     vm->bind_func<1>(mod, "dis", [](VM* vm, Args& args) {
         PyVar f = args[0];
         if(is_type(f, vm->tp_bound_method)) f = vm->PyBoundMethod_AS_C(args[0]).method;
-        CodeObject_ code = vm->PyFunction_AS_C(f).code;
+        CodeObject_ code = py_cast<Function>(vm, f).code;
         (*vm->_stdout) << vm->disassemble(code);
         return vm->None;
     });
@@ -636,31 +636,31 @@ struct FileIO {
     static void _register(VM* vm, PyVar mod, PyVar type){
         vm->bind_static_method<2>(type, "__new__", [](VM* vm, Args& args){
             return vm->new_object<FileIO>(
-                vm, vm->PyStr_AS_C(args[0]), vm->PyStr_AS_C(args[1])
+                vm, py_cast<Str>(vm, args[0]), py_cast<Str>(vm, args[1])
             );
         });
 
         vm->bind_method<0>(type, "read", [](VM* vm, Args& args){
-            FileIO& io = vm->py_cast<FileIO>(args[0]);
+            FileIO& io = vm->_cast<FileIO>(args[0]);
             std::string buffer;
             io._fs >> buffer;
-            return vm->PyStr(buffer);
+            return py_object(vm, buffer);
         });
 
         vm->bind_method<1>(type, "write", [](VM* vm, Args& args){
-            FileIO& io = vm->py_cast<FileIO>(args[0]);
-            io._fs << vm->PyStr_AS_C(args[1]);
+            FileIO& io = vm->_cast<FileIO>(args[0]);
+            io._fs << py_cast<Str>(vm, args[1]);
             return vm->None;
         });
 
         vm->bind_method<0>(type, "close", [](VM* vm, Args& args){
-            FileIO& io = vm->py_cast<FileIO>(args[0]);
+            FileIO& io = vm->_cast<FileIO>(args[0]);
             io._fs.close();
             return vm->None;
         });
 
         vm->bind_method<0>(type, "__exit__", [](VM* vm, Args& args){
-            FileIO& io = vm->py_cast<FileIO>(args[0]);
+            FileIO& io = vm->_cast<FileIO>(args[0]);
             io._fs.close();
             return vm->None;
         });
@@ -688,19 +688,19 @@ struct ReMatch {
 
     static void _register(VM* vm, PyVar mod, PyVar type){
         vm->bind_method<-1>(type, "__init__", CPP_NOT_IMPLEMENTED());
-        vm->bind_method<0>(type, "start", CPP_LAMBDA(py_object(vm, vm->py_cast<ReMatch>(args[0]).start)));
-        vm->bind_method<0>(type, "end", CPP_LAMBDA(py_object(vm, vm->py_cast<ReMatch>(args[0]).end)));
+        vm->bind_method<0>(type, "start", CPP_LAMBDA(py_object(vm, vm->_cast<ReMatch>(args[0]).start)));
+        vm->bind_method<0>(type, "end", CPP_LAMBDA(py_object(vm, vm->_cast<ReMatch>(args[0]).end)));
 
         vm->bind_method<0>(type, "span", [](VM* vm, Args& args) {
-            auto& self = vm->py_cast<ReMatch>(args[0]);
-            return vm->PyTuple({ py_object(vm, self.start), py_object(vm, self.end) });
+            auto& self = vm->_cast<ReMatch>(args[0]);
+            return py_object(vm, pkpy::Args({ py_object(vm, self.start), py_object(vm, self.end) }));
         });
 
         vm->bind_method<1>(type, "group", [](VM* vm, Args& args) {
-            auto& self = vm->py_cast<ReMatch>(args[0]);
+            auto& self = vm->_cast<ReMatch>(args[0]);
             int index = (int)py_cast_v<i64>(vm, args[1]);
             index = vm->normalized_index(index, self.m.size());
-            return vm->PyStr(self.m[index].str());
+            return py_object(vm, self.m[index].str());
         });
     }
 };
@@ -722,36 +722,36 @@ void add_module_re(VM* vm){
     vm->register_class<ReMatch>(mod);
 
     vm->bind_func<2>(mod, "match", [](VM* vm, Args& args) {
-        const Str& pattern = vm->PyStr_AS_C(args[0]);
-        const Str& string = vm->PyStr_AS_C(args[1]);
+        const Str& pattern = py_cast<Str>(vm, args[0]);
+        const Str& string = py_cast<Str>(vm, args[1]);
         return _regex_search(pattern, string, true, vm);
     });
 
     vm->bind_func<2>(mod, "search", [](VM* vm, Args& args) {
-        const Str& pattern = vm->PyStr_AS_C(args[0]);
-        const Str& string = vm->PyStr_AS_C(args[1]);
+        const Str& pattern = py_cast<Str>(vm, args[0]);
+        const Str& string = py_cast<Str>(vm, args[1]);
         return _regex_search(pattern, string, false, vm);
     });
 
     vm->bind_func<3>(mod, "sub", [](VM* vm, Args& args) {
-        const Str& pattern = vm->PyStr_AS_C(args[0]);
-        const Str& repl = vm->PyStr_AS_C(args[1]);
-        const Str& string = vm->PyStr_AS_C(args[2]);
+        const Str& pattern = py_cast<Str>(vm, args[0]);
+        const Str& repl = py_cast<Str>(vm, args[1]);
+        const Str& string = py_cast<Str>(vm, args[2]);
         std::regex re(pattern);
-        return vm->PyStr(std::regex_replace(string, re, repl));
+        return py_object(vm, std::regex_replace(string, re, repl));
     });
 
     vm->bind_func<2>(mod, "split", [](VM* vm, Args& args) {
-        const Str& pattern = vm->PyStr_AS_C(args[0]);
-        const Str& string = vm->PyStr_AS_C(args[1]);
+        const Str& pattern = py_cast<Str>(vm, args[0]);
+        const Str& string = py_cast<Str>(vm, args[1]);
         std::regex re(pattern);
         std::sregex_token_iterator it(string.begin(), string.end(), re, -1);
         std::sregex_token_iterator end;
         List vec;
         for(; it != end; ++it){
-            vec.push_back(vm->PyStr(it->str()));
+            vec.push_back(py_object(vm, it->str()));
         }
-        return vm->PyList(vec);
+        return py_object(vm, vec);
     });
 }
 
@@ -868,7 +868,7 @@ extern "C" {
         pkpy::PyVar* val = vm->_main->attr().try_get(name);
         if(val == nullptr) return nullptr;
         try{
-            pkpy::Str _repr = vm->PyStr_AS_C(vm->asRepr(*val));
+            pkpy::Str& _repr = pkpy::py_cast<pkpy::Str>(vm, vm->asRepr(*val));
             return strdup(_repr.c_str());
         }catch(...){
             return nullptr;
@@ -884,7 +884,7 @@ extern "C" {
         pkpy::PyVarOrNull ret = vm->exec(source, "<eval>", pkpy::EVAL_MODE);
         if(ret == nullptr) return nullptr;
         try{
-            pkpy::Str _repr = vm->PyStr_AS_C(vm->asRepr(ret));
+            pkpy::Str& _repr = pkpy::py_cast<pkpy::Str>(vm, vm->asRepr(ret));
             return strdup(_repr.c_str());
         }catch(...){
             return nullptr;
@@ -971,7 +971,7 @@ extern "C" {
             for(int i=0; i<args.size(); i++){
                 ss << ' ';
                 pkpy::PyVar x = vm->call(args[i], pkpy::__json__);
-                ss << vm->PyStr_AS_C(x);
+                ss << pkpy::py_cast<pkpy::Str>(vm, x);
             }
             char* packet = strdup(ss.str().c_str());
             switch(ret_code){
@@ -981,7 +981,7 @@ extern "C" {
                 case 's': {
                     char* p = f_str(packet);
                     if(p == nullptr) return vm->None;
-                    return vm->PyStr(p); // no need to free(p)
+                    return py_object(vm, p); // no need to free(p)
                 }
                 case 'N': f_None(packet); return vm->None;
             }
diff --git a/src/ref.h b/src/ref.h
index 5e7e8e5f..aa16f640 100644
--- a/src/ref.h
+++ b/src/ref.h
@@ -118,7 +118,7 @@ struct TupleRef : BaseRef {
         for (int i = 0; i < objs.size(); i++) {
             args[i] = vm->PyRef_AS_C(objs[i])->get(vm, frame);
         }
-        return vm->PyTuple(std::move(args));
+        return py_object(vm, std::move(args));
     }
 
     void set(VM* vm, Frame* frame, PyVar val) const{
@@ -133,7 +133,7 @@ struct TupleRef : BaseRef {
                 auto ref = vm->PyRef_AS_C(star.obj);
                 List list;
                 while((x = iter->next()) != nullptr) list.push_back(x);
-                ref->set(vm, frame, vm->PyList(std::move(list)));
+                ref->set(vm, frame, py_object(vm, std::move(list)));
                 return;
             }else{
                 x = iter->next();
diff --git a/src/tuplelist.h b/src/tuplelist.h
index f7589173..9cf1c4f9 100644
--- a/src/tuplelist.h
+++ b/src/tuplelist.h
@@ -39,11 +39,12 @@ namespace pkpy {
             other._size = 0;
         }
 
-        Args(List&& other) noexcept {
-            _alloc(other.size());
-            memcpy((void*)_args, (void*)other.data(), sizeof(PyVar)*_size);
-            memset((void*)other.data(), 0, sizeof(PyVar)*_size);
+        static pkpy::Args from_list(List&& other) noexcept {
+            Args ret(other.size());
+            memcpy((void*)ret._args, (void*)other.data(), sizeof(PyVar)*ret.size());
+            memset((void*)other.data(), 0, sizeof(PyVar)*ret.size());
             other.clear();
+            return ret;
         }
 
         PyVar& operator[](int i){ return _args[i]; }
diff --git a/src/vm.h b/src/vm.h
index e1eaa4b6..f06f4551 100644
--- a/src/vm.h
+++ b/src/vm.h
@@ -21,6 +21,13 @@ namespace pkpy{
     template<> ctype& _py_cast<ctype>(VM* vm, const PyVar& obj) {       \
         return OBJ_GET(ctype, obj);                                     \
     }                                                                   \
+    template<> ctype py_cast_v<ctype>(VM* vm, const PyVar& obj) {       \
+        vm->check_type(obj, vm->ptype);                                 \
+        return OBJ_GET(ctype, obj);                                     \
+    }                                                                   \
+    template<> ctype _py_cast_v<ctype>(VM* vm, const PyVar& obj) {      \
+        return OBJ_GET(ctype, obj);                                     \
+    }                                                                   \
     PyVar py_object(VM* vm, const ctype& value) { return vm->new_object(vm->ptype, value);}     \
     PyVar py_object(VM* vm, ctype&& value) { return vm->new_object(vm->ptype, std::move(value));}
 
@@ -84,11 +91,6 @@ public:
         return callstack.top().get();
     }
 
-    PyVar asRepr(const PyVar& obj){
-        if(is_type(obj, tp_type)) return PyStr("<class '" + OBJ_GET(Str, obj->attr(__name__)) + "'>");
-        return call(obj, __repr__);
-    }
-
     PyVar asIter(const PyVar& obj){
         if(is_type(obj, tp_native_iterator)) return obj;
         PyVarOrNull iter_f = getattr(obj, __iter__, false);
@@ -133,82 +135,6 @@ public:
         return call(getattr(obj, name), no_arg(), no_arg(), false);
     }
 
-    PyVar call(const PyVar& _callable, Args args, const Args& kwargs, bool opCall){
-        if(is_type(_callable, tp_type)){
-            PyVar* new_f = _callable->attr().try_get(__new__);
-            PyVar obj;
-            if(new_f != nullptr){
-                obj = call(*new_f, std::move(args), kwargs, false);
-            }else{
-                obj = new_object(_callable, DummyInstance());
-                PyVarOrNull init_f = getattr(obj, __init__, false);
-                if (init_f != nullptr) call(init_f, std::move(args), kwargs, false);
-            }
-            return obj;
-        }
-
-        const PyVar* callable = &_callable;
-        if(is_type(*callable, tp_bound_method)){
-            auto& bm = PyBoundMethod_AS_C((*callable));
-            callable = &bm.method;      // get unbound method
-            args.extend_self(bm.obj);
-        }
-        
-        if(is_type(*callable, tp_native_function)){
-            const auto& f = OBJ_GET(NativeFunc, *callable);
-            if(kwargs.size() != 0) TypeError("native_function does not accept keyword arguments");
-            return f(this, args);
-        } else if(is_type(*callable, tp_function)){
-            const Function& fn = PyFunction_AS_C(*callable);
-            NameDict_ locals = make_sp<NameDict>(
-                fn.code->perfect_locals_capacity,
-                kLocalsLoadFactor,
-                fn.code->perfect_hash_seed
-            );
-
-            int i = 0;
-            for(StrName name : fn.args){
-                if(i < args.size()){
-                    locals->set(name, std::move(args[i++]));
-                    continue;
-                }
-                TypeError("missing positional argument " + name.str().escape(true));
-            }
-
-            locals->update(fn.kwargs);
-
-            if(!fn.starred_arg.empty()){
-                List vargs;        // handle *args
-                while(i < args.size()) vargs.push_back(std::move(args[i++]));
-                locals->set(fn.starred_arg, PyTuple(std::move(vargs)));
-            }else{
-                for(StrName key : fn.kwargs_order){
-                    if(i < args.size()){
-                        locals->set(key, std::move(args[i++]));
-                    }else{
-                        break;
-                    }
-                }
-                if(i < args.size()) TypeError("too many arguments");
-            }
-            
-            for(int i=0; i<kwargs.size(); i+=2){
-                const Str& key = PyStr_AS_C(kwargs[i]);
-                if(!fn.kwargs.contains(key)){
-                    TypeError(key.escape(true) + " is an invalid keyword argument for " + fn.name.str() + "()");
-                }
-                locals->set(key, kwargs[i+1]);
-            }
-            const PyVar& _module = fn._module != nullptr ? fn._module : top_frame()->_module;
-            auto _frame = _new_frame(fn.code, _module, locals, fn._closure);
-            if(fn.code->is_generator) return PyIter(Generator(this, std::move(_frame)));
-            callstack.push(std::move(_frame));
-            if(opCall) return _py_op_call;
-            return _exec();
-        }
-        TypeError(OBJ_NAME(_t(*callable)).escape(true) + " object is not callable");
-        return None;
-    }
 
     // repl mode is only for setting `frame->id` to 0
     PyVarOrNull exec(Str source, Str filename, CompileMode mode, PyVar _module=nullptr){
@@ -282,18 +208,6 @@ public:
         }
     }
 
-    PyVar new_type_object(PyVar mod, StrName name, PyVar base){
-        if(!is_type(base, tp_type)) UNREACHABLE();
-        PyVar obj = make_sp<PyObject, Py_<Type>>(tp_type, _all_types.size());
-        setattr(obj, __base__, base);
-        Str fullName = name.str();
-        if(mod != builtins) fullName = OBJ_NAME(mod) + "." + name.str();
-        setattr(obj, __name__, PyStr(fullName));
-        setattr(mod, name, obj);
-        _all_types.push_back(obj);
-        return obj;
-    }
-
     Type _new_type_object(StrName name, Type base=0) {
         PyVar obj = make_sp<PyObject, Py_<Type>>(tp_type, _all_types.size());
         setattr(obj, __base__, _t(base));
@@ -331,13 +245,6 @@ public:
         return new_object(T::_type(this), T(std::forward<Args>(args)...));
     }
 
-    PyVar new_module(StrName name) {
-        PyVar obj = new_object(tp_module, DummyModule());
-        setattr(obj, __name__, PyStr(name.str()));
-        _modules.set(name, obj);
-        return obj;
-    }
-
     PyVarOrNull getattr(const PyVar& obj, StrName name, bool throw_err=true) {
         PyVar* val;
         PyObject* cls;
@@ -435,75 +342,6 @@ public:
         return index;
     }
 
-    Str disassemble(CodeObject_ co){
-        std::vector<int> jumpTargets;
-        for(auto byte : co->codes){
-            if(byte.op == OP_JUMP_ABSOLUTE || byte.op == OP_SAFE_JUMP_ABSOLUTE || byte.op == OP_POP_JUMP_IF_FALSE){
-                jumpTargets.push_back(byte.arg);
-            }
-        }
-        StrStream ss;
-        ss << std::string(54, '-') << '\n';
-        ss << co->name << ":\n";
-        int prev_line = -1;
-        for(int i=0; i<co->codes.size(); i++){
-            const Bytecode& byte = co->codes[i];
-            if(byte.op == OP_NO_OP) continue;
-            Str line = std::to_string(byte.line);
-            if(byte.line == prev_line) line = "";
-            else{
-                if(prev_line != -1) ss << "\n";
-                prev_line = byte.line;
-            }
-
-            std::string pointer;
-            if(std::find(jumpTargets.begin(), jumpTargets.end(), i) != jumpTargets.end()){
-                pointer = "-> ";
-            }else{
-                pointer = "   ";
-            }
-            ss << pad(line, 8) << pointer << pad(std::to_string(i), 3);
-            ss << " " << pad(OP_NAMES[byte.op], 20) << " ";
-            // ss << pad(byte.arg == -1 ? "" : std::to_string(byte.arg), 5);
-            std::string argStr = byte.arg == -1 ? "" : std::to_string(byte.arg);
-            if(byte.op == OP_LOAD_CONST){
-                argStr += " (" + PyStr_AS_C(asRepr(co->consts[byte.arg])) + ")";
-            }
-            if(byte.op == OP_LOAD_NAME_REF || byte.op == OP_LOAD_NAME || byte.op == OP_RAISE || byte.op == OP_STORE_NAME){
-                argStr += " (" + co->names[byte.arg].first.str().escape(true) + ")";
-            }
-            if(byte.op == OP_FAST_INDEX || byte.op == OP_FAST_INDEX_REF){
-                auto& a = co->names[byte.arg & 0xFFFF];
-                auto& x = co->names[(byte.arg >> 16) & 0xFFFF];
-                argStr += " (" + a.first.str() + '[' + x.first.str() + "])";
-            }
-            ss << pad(argStr, 20);      // may overflow
-            ss << co->blocks[byte.block].to_string();
-            if(i != co->codes.size() - 1) ss << '\n';
-        }
-        StrStream consts;
-        consts << "co_consts: ";
-        consts << PyStr_AS_C(asRepr(PyList(co->consts)));
-
-        StrStream names;
-        names << "co_names: ";
-        List list;
-        for(int i=0; i<co->names.size(); i++){
-            list.push_back(PyStr(co->names[i].first.str()));
-        }
-        names << PyStr_AS_C(asRepr(PyList(list)));
-        ss << '\n' << consts.str() << '\n' << names.str() << '\n';
-
-        for(int i=0; i<co->consts.size(); i++){
-            PyVar obj = co->consts[i];
-            if(is_type(obj, tp_function)){
-                const auto& f = PyFunction_AS_C(obj);
-                ss << disassemble(f.code);
-            }
-        }
-        return Str(ss.str());
-    }
-
     // for quick access
     Type tp_object, tp_type, tp_int, tp_float, tp_bool, tp_str;
     Type tp_list, tp_tuple;
@@ -523,10 +361,6 @@ public:
         return static_cast<BaseIter*>(obj->value());
     }
 
-    DEF_NATIVE(Str, Str, tp_str)
-    DEF_NATIVE(List, List, tp_list)
-    DEF_NATIVE(Tuple, Tuple, tp_tuple)
-    DEF_NATIVE(Function, Function, tp_function)
     DEF_NATIVE(NativeFunc, NativeFunc, tp_native_function)
     DEF_NATIVE(BoundMethod, BoundMethod, tp_bound_method)
     DEF_NATIVE(Range, Range, tp_range)
@@ -542,63 +376,6 @@ public:
     inline bool _PyBool_AS_C(const PyVar& obj){ return obj == True; }
     inline const PyVar& PyBool(bool value){return value ? True : False;}
 
-    void init_builtin_types(){
-        PyVar _tp_object = make_sp<PyObject, Py_<Type>>(1, 0);
-        PyVar _tp_type = make_sp<PyObject, Py_<Type>>(1, 1);
-        _all_types.push_back(_tp_object);
-        _all_types.push_back(_tp_type);
-        tp_object = 0; tp_type = 1;
-
-        _types.set("object", _tp_object);
-        _types.set("type", _tp_type);
-
-        tp_int = _new_type_object("int");
-        tp_float = _new_type_object("float");
-        if(tp_int.index != kTpIntIndex || tp_float.index != kTpFloatIndex) UNREACHABLE();
-
-        tp_bool = _new_type_object("bool");
-        tp_str = _new_type_object("str");
-        tp_list = _new_type_object("list");
-        tp_tuple = _new_type_object("tuple");
-        tp_slice = _new_type_object("slice");
-        tp_range = _new_type_object("range");
-        tp_module = _new_type_object("module");
-        tp_ref = _new_type_object("_ref");
-        tp_star_wrapper = _new_type_object("_star_wrapper");
-        
-        tp_function = _new_type_object("function");
-        tp_native_function = _new_type_object("native_function");
-        tp_native_iterator = _new_type_object("native_iterator");
-        tp_bound_method = _new_type_object("bound_method");
-        tp_super = _new_type_object("super");
-        tp_exception = _new_type_object("Exception");
-
-        this->None = new_object(_new_type_object("NoneType"), DUMMY_VAL);
-        this->Ellipsis = new_object(_new_type_object("ellipsis"), DUMMY_VAL);
-        this->True = new_object(tp_bool, true);
-        this->False = new_object(tp_bool, false);
-        this->builtins = new_module("builtins");
-        this->_main = new_module("__main__");
-        this->_py_op_call = new_object(_new_type_object("_py_op_call"), DUMMY_VAL);
-        this->_py_op_yield = new_object(_new_type_object("_py_op_yield"), DUMMY_VAL);
-
-        setattr(_t(tp_type), __base__, _t(tp_object));
-        setattr(_t(tp_object), __base__, None);
-        
-        for(auto [k, v]: _types.items()){
-            setattr(v, __name__, PyStr(k.str()));
-        }
-
-        std::vector<Str> pb_types = {"type", "object", "bool", "int", "float", "str", "list", "tuple", "range"};
-        for (auto& name : pb_types) {
-            setattr(builtins, name, _types[name]);
-        }
-
-        post_init();
-        for(auto [k, v]: _types.items()) v->attr()._try_perfect_rehash();
-        for(auto [k, v]: _modules.items()) v->attr()._try_perfect_rehash();
-    }
-
     /***** Error Reporter *****/
     void _error(StrName name, const Str& msg){
         _error(Exception(name, msg));
@@ -659,27 +436,11 @@ public:
     }
 
     template<typename T>
-    inline T& py_cast(const PyVar& obj){
+    inline T& _cast(const PyVar& obj){
         check_type(obj, T::_type(this));
         return OBJ_GET(T, obj);
     }
 
-    void unpack_args(Args& args){
-        List unpacked;
-        for(int i=0; i<args.size(); i++){
-            if(is_type(args[i], tp_star_wrapper)){
-                auto& star = PyStarWrapper_AS_C(args[i]);
-                if(!star.rvalue) UNREACHABLE();
-                PyVar list = asList(star.obj);
-                List& list_c = PyList_AS_C(list);
-                unpacked.insert(unpacked.end(), list_c.begin(), list_c.end());
-            }else{
-                unpacked.push_back(args[i]);
-            }
-        }
-        args = std::move(unpacked);
-    }
-
     ~VM() {
         if(!use_stdio){
             delete _stdout;
@@ -693,6 +454,13 @@ public:
     f64 num_to_float(const PyVar& obj);
     const PyVar& asBool(const PyVar& obj);
     i64 hash(const PyVar& obj);
+    PyVar asRepr(const PyVar& obj);
+    PyVar new_type_object(PyVar mod, StrName name, PyVar base);
+    PyVar new_module(StrName name);
+    Str disassemble(CodeObject_ co);
+    void init_builtin_types();
+    PyVar call(const PyVar& _callable, Args args, const Args& kwargs, bool opCall);
+    void unpack_args(Args& args);
 
     template<typename P>
     PyVarRef PyRef(P&& value);
@@ -740,8 +508,19 @@ void CodeObject::optimize(VM* vm){
     }
 }
 
+DEF_NATIVE_2(Str, tp_str)
+DEF_NATIVE_2(List, tp_list)
+DEF_NATIVE_2(Tuple, tp_tuple)
+DEF_NATIVE_2(Function, tp_function)
+DEF_NATIVE_2(NativeFunc, tp_native_function)
+DEF_NATIVE_2(BoundMethod, tp_bound_method)
+DEF_NATIVE_2(Range, tp_range)
+DEF_NATIVE_2(Slice, tp_slice)
+DEF_NATIVE_2(Exception, tp_exception)
+DEF_NATIVE_2(StarWrapper, tp_star_wrapper)
+
 template<typename T>
-std::enable_if_t<std::is_integral_v<T>, PyVar> py_object(VM* vm, T _val){
+std::enable_if_t<std::is_integral_v<T> && !std::is_same_v<T, bool>, PyVar> py_object(VM* vm, T _val){
     i64 val = static_cast<i64>(_val);
     if(((val << 2) >> 2) != val){
         vm->_error("OverflowError", std::to_string(val) + " is out of range");
@@ -786,17 +565,9 @@ template<> bool _py_cast_v<bool>(VM* vm, const PyVar& obj){
     return obj == vm->True;
 }
 
-DEF_NATIVE_2(Str, tp_str)
-DEF_NATIVE_2(List, tp_list)
-DEF_NATIVE_2(Tuple, tp_tuple)
-DEF_NATIVE_2(Function, tp_function)
-DEF_NATIVE_2(NativeFunc, tp_native_function)
-DEF_NATIVE_2(BoundMethod, tp_bound_method)
-DEF_NATIVE_2(Range, tp_range)
-DEF_NATIVE_2(Slice, tp_slice)
-DEF_NATIVE_2(Exception, tp_exception)
-DEF_NATIVE_2(StarWrapper, tp_star_wrapper)
-
+PyVar py_object(VM* vm, const char* val){
+    return py_object(vm, Str(val));
+}
 
 PyVar VM::num_negated(const PyVar& obj){
     if (is_int(obj)){
@@ -832,11 +603,11 @@ const PyVar& VM::asBool(const PyVar& obj){
 }
 
 i64 VM::hash(const PyVar& obj){
-    if (is_type(obj, tp_str)) return PyStr_AS_C(obj).hash();
+    if (is_type(obj, tp_str)) return py_cast<Str>(this, obj).hash();
     if (is_int(obj)) return py_cast_v<i64>(this, obj);
     if (is_type(obj, tp_tuple)) {
         i64 x = 1000003;
-        const Tuple& items = PyTuple_AS_C(obj);
+        const Tuple& items = py_cast<Tuple>(this, obj);
         for (int i=0; i<items.size(); i++) {
             i64 y = hash(items[i]);
             x = x ^ (y + 0x9e3779b9 + (x << 6) + (x >> 2)); // recommended by Github Copilot
@@ -853,4 +624,247 @@ i64 VM::hash(const PyVar& obj){
     return 0;
 }
 
+PyVar VM::asRepr(const PyVar& obj){
+    if(is_type(obj, tp_type)) return py_object(this, "<class '" + OBJ_GET(Str, obj->attr(__name__)) + "'>");
+    return call(obj, __repr__);
+}
+
+PyVar VM::new_type_object(PyVar mod, StrName name, PyVar base){
+    if(!is_type(base, tp_type)) UNREACHABLE();
+    PyVar obj = make_sp<PyObject, Py_<Type>>(tp_type, _all_types.size());
+    setattr(obj, __base__, base);
+    Str fullName = name.str();
+    if(mod != builtins) fullName = OBJ_NAME(mod) + "." + name.str();
+    setattr(obj, __name__, py_object(this, fullName));
+    setattr(mod, name, obj);
+    _all_types.push_back(obj);
+    return obj;
+}
+
+PyVar VM::new_module(StrName name) {
+    PyVar obj = new_object(tp_module, DummyModule());
+    setattr(obj, __name__, py_object(this, name.str()));
+    _modules.set(name, obj);
+    return obj;
+}
+
+Str VM::disassemble(CodeObject_ co){
+    std::vector<int> jumpTargets;
+    for(auto byte : co->codes){
+        if(byte.op == OP_JUMP_ABSOLUTE || byte.op == OP_SAFE_JUMP_ABSOLUTE || byte.op == OP_POP_JUMP_IF_FALSE){
+            jumpTargets.push_back(byte.arg);
+        }
+    }
+    StrStream ss;
+    ss << std::string(54, '-') << '\n';
+    ss << co->name << ":\n";
+    int prev_line = -1;
+    for(int i=0; i<co->codes.size(); i++){
+        const Bytecode& byte = co->codes[i];
+        if(byte.op == OP_NO_OP) continue;
+        Str line = std::to_string(byte.line);
+        if(byte.line == prev_line) line = "";
+        else{
+            if(prev_line != -1) ss << "\n";
+            prev_line = byte.line;
+        }
+
+        std::string pointer;
+        if(std::find(jumpTargets.begin(), jumpTargets.end(), i) != jumpTargets.end()){
+            pointer = "-> ";
+        }else{
+            pointer = "   ";
+        }
+        ss << pad(line, 8) << pointer << pad(std::to_string(i), 3);
+        ss << " " << pad(OP_NAMES[byte.op], 20) << " ";
+        // ss << pad(byte.arg == -1 ? "" : std::to_string(byte.arg), 5);
+        std::string argStr = byte.arg == -1 ? "" : std::to_string(byte.arg);
+        if(byte.op == OP_LOAD_CONST){
+            argStr += " (" + py_cast<Str>(this, asRepr(co->consts[byte.arg])) + ")";
+        }
+        if(byte.op == OP_LOAD_NAME_REF || byte.op == OP_LOAD_NAME || byte.op == OP_RAISE || byte.op == OP_STORE_NAME){
+            argStr += " (" + co->names[byte.arg].first.str().escape(true) + ")";
+        }
+        if(byte.op == OP_FAST_INDEX || byte.op == OP_FAST_INDEX_REF){
+            auto& a = co->names[byte.arg & 0xFFFF];
+            auto& x = co->names[(byte.arg >> 16) & 0xFFFF];
+            argStr += " (" + a.first.str() + '[' + x.first.str() + "])";
+        }
+        ss << pad(argStr, 20);      // may overflow
+        ss << co->blocks[byte.block].to_string();
+        if(i != co->codes.size() - 1) ss << '\n';
+    }
+    StrStream consts;
+    consts << "co_consts: ";
+    consts << py_cast<Str>(this, asRepr(py_object(this, co->consts)));
+
+    StrStream names;
+    names << "co_names: ";
+    List list;
+    for(int i=0; i<co->names.size(); i++){
+        list.push_back(py_object(this, co->names[i].first.str()));
+    }
+    names << py_cast<Str>(this, asRepr(py_object(this, list)));
+    ss << '\n' << consts.str() << '\n' << names.str() << '\n';
+
+    for(int i=0; i<co->consts.size(); i++){
+        PyVar obj = co->consts[i];
+        if(is_type(obj, tp_function)){
+            const auto& f = py_cast<Function>(this, obj);
+            ss << disassemble(f.code);
+        }
+    }
+    return Str(ss.str());
+}
+
+void VM::init_builtin_types(){
+    PyVar _tp_object = make_sp<PyObject, Py_<Type>>(1, 0);
+    PyVar _tp_type = make_sp<PyObject, Py_<Type>>(1, 1);
+    _all_types.push_back(_tp_object);
+    _all_types.push_back(_tp_type);
+    tp_object = 0; tp_type = 1;
+
+    _types.set("object", _tp_object);
+    _types.set("type", _tp_type);
+
+    tp_int = _new_type_object("int");
+    tp_float = _new_type_object("float");
+    if(tp_int.index != kTpIntIndex || tp_float.index != kTpFloatIndex) UNREACHABLE();
+
+    tp_bool = _new_type_object("bool");
+    tp_str = _new_type_object("str");
+    tp_list = _new_type_object("list");
+    tp_tuple = _new_type_object("tuple");
+    tp_slice = _new_type_object("slice");
+    tp_range = _new_type_object("range");
+    tp_module = _new_type_object("module");
+    tp_ref = _new_type_object("_ref");
+    tp_star_wrapper = _new_type_object("_star_wrapper");
+    
+    tp_function = _new_type_object("function");
+    tp_native_function = _new_type_object("native_function");
+    tp_native_iterator = _new_type_object("native_iterator");
+    tp_bound_method = _new_type_object("bound_method");
+    tp_super = _new_type_object("super");
+    tp_exception = _new_type_object("Exception");
+
+    this->None = new_object(_new_type_object("NoneType"), DUMMY_VAL);
+    this->Ellipsis = new_object(_new_type_object("ellipsis"), DUMMY_VAL);
+    this->True = new_object(tp_bool, true);
+    this->False = new_object(tp_bool, false);
+    this->builtins = new_module("builtins");
+    this->_main = new_module("__main__");
+    this->_py_op_call = new_object(_new_type_object("_py_op_call"), DUMMY_VAL);
+    this->_py_op_yield = new_object(_new_type_object("_py_op_yield"), DUMMY_VAL);
+
+    setattr(_t(tp_type), __base__, _t(tp_object));
+    setattr(_t(tp_object), __base__, None);
+    
+    for(auto [k, v]: _types.items()){
+        setattr(v, __name__, py_object(this, k.str()));
+    }
+
+    std::vector<Str> pb_types = {"type", "object", "bool", "int", "float", "str", "list", "tuple", "range"};
+    for (auto& name : pb_types) {
+        setattr(builtins, name, _types[name]);
+    }
+
+    post_init();
+    for(auto [k, v]: _types.items()) v->attr()._try_perfect_rehash();
+    for(auto [k, v]: _modules.items()) v->attr()._try_perfect_rehash();
+}
+
+PyVar VM::call(const PyVar& _callable, Args args, const Args& kwargs, bool opCall){
+    if(is_type(_callable, tp_type)){
+        PyVar* new_f = _callable->attr().try_get(__new__);
+        PyVar obj;
+        if(new_f != nullptr){
+            obj = call(*new_f, std::move(args), kwargs, false);
+        }else{
+            obj = new_object(_callable, DummyInstance());
+            PyVarOrNull init_f = getattr(obj, __init__, false);
+            if (init_f != nullptr) call(init_f, std::move(args), kwargs, false);
+        }
+        return obj;
+    }
+
+    const PyVar* callable = &_callable;
+    if(is_type(*callable, tp_bound_method)){
+        auto& bm = PyBoundMethod_AS_C((*callable));
+        callable = &bm.method;      // get unbound method
+        args.extend_self(bm.obj);
+    }
+    
+    if(is_type(*callable, tp_native_function)){
+        const auto& f = OBJ_GET(NativeFunc, *callable);
+        if(kwargs.size() != 0) TypeError("native_function does not accept keyword arguments");
+        return f(this, args);
+    } else if(is_type(*callable, tp_function)){
+        const Function& fn = py_cast<Function>(this, *callable);
+        NameDict_ locals = make_sp<NameDict>(
+            fn.code->perfect_locals_capacity,
+            kLocalsLoadFactor,
+            fn.code->perfect_hash_seed
+        );
+
+        int i = 0;
+        for(StrName name : fn.args){
+            if(i < args.size()){
+                locals->set(name, std::move(args[i++]));
+                continue;
+            }
+            TypeError("missing positional argument " + name.str().escape(true));
+        }
+
+        locals->update(fn.kwargs);
+
+        if(!fn.starred_arg.empty()){
+            List vargs;        // handle *args
+            while(i < args.size()) vargs.push_back(std::move(args[i++]));
+            locals->set(fn.starred_arg, py_object(this, Tuple::from_list(std::move(vargs))));
+        }else{
+            for(StrName key : fn.kwargs_order){
+                if(i < args.size()){
+                    locals->set(key, std::move(args[i++]));
+                }else{
+                    break;
+                }
+            }
+            if(i < args.size()) TypeError("too many arguments");
+        }
+        
+        for(int i=0; i<kwargs.size(); i+=2){
+            const Str& key = py_cast<Str>(this, kwargs[i]);
+            if(!fn.kwargs.contains(key)){
+                TypeError(key.escape(true) + " is an invalid keyword argument for " + fn.name.str() + "()");
+            }
+            locals->set(key, kwargs[i+1]);
+        }
+        const PyVar& _module = fn._module != nullptr ? fn._module : top_frame()->_module;
+        auto _frame = _new_frame(fn.code, _module, locals, fn._closure);
+        if(fn.code->is_generator) return PyIter(Generator(this, std::move(_frame)));
+        callstack.push(std::move(_frame));
+        if(opCall) return _py_op_call;
+        return _exec();
+    }
+    TypeError(OBJ_NAME(_t(*callable)).escape(true) + " object is not callable");
+    return None;
+}
+
+void VM::unpack_args(Args& args){
+    List unpacked;
+    for(int i=0; i<args.size(); i++){
+        if(is_type(args[i], tp_star_wrapper)){
+            auto& star = PyStarWrapper_AS_C(args[i]);
+            if(!star.rvalue) UNREACHABLE();
+            PyVar list = asList(star.obj);
+            List& list_c = py_cast<List>(this, list);
+            unpacked.insert(unpacked.end(), list_c.begin(), list_c.end());
+        }else{
+            unpacked.push_back(args[i]);
+        }
+    }
+    args = Args::from_list(std::move(unpacked));
+}
+
 }   // namespace pkpy
\ No newline at end of file