diff --git a/docs/modules/sys.md b/docs/modules/sys.md
index 86a44d13..ab9ac723 100644
--- a/docs/modules/sys.md
+++ b/docs/modules/sys.md
@@ -15,8 +15,4 @@ May be one of:
 + `darwin`
 + `android`
 + `ios`
-+ `emscripten`
-
-### `sys._repl()`
-
-Get a REPL for this vm. Use its `input` method to feed strings to the REPL. This function is experimental.
\ No newline at end of file
++ `emscripten`
\ No newline at end of file
diff --git a/include/pocketpy/pocketpy_c.h b/include/pocketpy/pocketpy_c.h
index 70d75555..628cb263 100644
--- a/include/pocketpy/pocketpy_c.h
+++ b/include/pocketpy/pocketpy_c.h
@@ -12,6 +12,7 @@ extern "C" {
 
 typedef struct pkpy_vm_handle pkpy_vm;
 typedef int (*pkpy_CFunction)(pkpy_vm*);
+typedef void (*pkpy_COutputHandler)(pkpy_vm*, const char*, int);
 typedef int pkpy_CName;
 typedef int pkpy_CType;
 
@@ -92,6 +93,7 @@ PK_EXPORT pkpy_CString pkpy_string(const char* s);
 PK_EXPORT pkpy_CName pkpy_name(const char* s);
 PK_EXPORT pkpy_CString pkpy_name_to_string(pkpy_CName name);
 PK_EXPORT void pkpy_compile_to_string(pkpy_vm*, const char* source, const char* filename, int mode, bool* ok, char** out);
+PK_EXPORT void pkpy_set_output_handler(pkpy_vm*, pkpy_COutputHandler handler);
 
 /* REPL */
 PK_EXPORT void* pkpy_new_repl(pkpy_vm*);
diff --git a/include/pocketpy/vm.h b/include/pocketpy/vm.h
index 3fd67e05..0349e335 100644
--- a/include/pocketpy/vm.h
+++ b/include/pocketpy/vm.h
@@ -104,7 +104,7 @@ struct FrameId{
     Frame* get() const { return &data->operator[](index); }
 };
 
-typedef void(*PrintFunc)(VM*, const Str&);
+typedef void(*PrintFunc)(VM*, const char*, int);
 
 class VM {
     PK_ALWAYS_PASS_BY_POINTER(VM)
@@ -181,6 +181,10 @@ public:
     void _push_varargs(PyObject* _0, PyObject* _1, PyObject* _2){ PUSH(_0); PUSH(_1); PUSH(_2); }
     void _push_varargs(PyObject* _0, PyObject* _1, PyObject* _2, PyObject* _3){ PUSH(_0); PUSH(_1); PUSH(_2); PUSH(_3); }
 
+    void stdout_write(const Str& s){
+        _stdout(this, s.data, s.size);
+    }
+
     template<typename... Args>
     PyObject* call(PyObject* callable, Args&&... args){
         PUSH(callable);
diff --git a/src/ceval.cpp b/src/ceval.cpp
index 93d8f120..ef83aadd 100644
--- a/src/ceval.cpp
+++ b/src/ceval.cpp
@@ -73,7 +73,7 @@ __NEXT_STEP:;
         THIRD() = _0;
         DISPATCH();
     TARGET(PRINT_EXPR)
-        if(TOP() != None) _stdout(this, CAST(Str&, py_repr(TOP())) + "\n");
+        if(TOP() != None) stdout_write(CAST(Str&, py_repr(TOP())) + "\n");
         POP();
         DISPATCH();
     /*****************************************/
diff --git a/src/pocketpy.cpp b/src/pocketpy.cpp
index 09677fe5..2272b282 100644
--- a/src/pocketpy.cpp
+++ b/src/pocketpy.cpp
@@ -1293,59 +1293,8 @@ void add_module_time(VM* vm){
     });
 }
 
-struct PyREPL{
-    PY_CLASS(PyREPL, sys, _repl)
-
-    REPL* repl;
-
-    PyREPL(VM* vm){ repl = new REPL(vm); }
-    ~PyREPL(){ delete repl; }
-
-    PyREPL(const PyREPL&) = delete;
-    PyREPL& operator=(const PyREPL&) = delete;
-
-    PyREPL(PyREPL&& other) noexcept{
-        repl = other.repl;
-        other.repl = nullptr;
-    }
-
-    struct TempOut{
-        PrintFunc backup;
-        VM* vm;
-        TempOut(VM* vm, PrintFunc f){
-            this->vm = vm;
-            this->backup = vm->_stdout;
-            vm->_stdout = f;
-        }
-        ~TempOut(){
-            vm->_stdout = backup;
-        }
-        TempOut(const TempOut&) = delete;
-        TempOut& operator=(const TempOut&) = delete;
-        TempOut(TempOut&&) = delete;
-        TempOut& operator=(TempOut&&) = delete;
-    };
-
-    static void _register(VM* vm, PyObject* mod, PyObject* type){
-        vm->bind_constructor<1>(type, [](VM* vm, ArgsView args){
-            return VAR_T(PyREPL, vm);
-        });
-
-        vm->bind_method<1>(type, "input", [](VM* vm, ArgsView args){
-            PyREPL& self = _CAST(PyREPL&, args[0]);
-            const Str& s = CAST(Str&, args[1]);
-            PK_LOCAL_STATIC std::stringstream ss_out;
-            ss_out.str("");
-            TempOut _(vm, [](VM* vm, const Str& s){ ss_out << s; });
-            bool ok = self.repl->input(s.str());
-            return VAR(Tuple({VAR(ok), VAR(ss_out.str())}));
-        });
-    }
-};
-
 void add_module_sys(VM* vm){
     PyObject* mod = vm->new_module("sys");
-    PyREPL::register_class(vm, mod);
     vm->setattr(mod, "version", VAR(PK_VERSION));
     vm->setattr(mod, "platform", VAR(PK_SYS_PLATFORM));
 
@@ -1355,12 +1304,14 @@ void add_module_sys(VM* vm){
     vm->setattr(mod, "stderr", stderr_);
 
     vm->bind_func<1>(stdout_, "write", [](VM* vm, ArgsView args) {
-        vm->_stdout(vm, CAST(Str&, args[0]));
+        Str& s = CAST(Str&, args[0]);
+        vm->_stdout(vm, s.data, s.size);
         return vm->None;
     });
 
     vm->bind_func<1>(stderr_, "write", [](VM* vm, ArgsView args) {
-        vm->_stderr(vm, CAST(Str&, args[0]));
+        Str& s = CAST(Str&, args[0]);
+        vm->_stderr(vm, s.data, s.size);
         return vm->None;
     });
 }
@@ -1460,7 +1411,8 @@ void add_module_traceback(VM* vm){
     vm->bind_func<0>(mod, "print_exc", [](VM* vm, ArgsView args) {
         if(vm->_last_exception==nullptr) vm->ValueError("no exception");
         Exception& e = CAST(Exception&, vm->_last_exception);
-        vm->_stdout(vm, e.summary());
+        Str sum = e.summary();
+        vm->_stdout(vm, sum.data, sum.size);
         return vm->None;
     });
 
@@ -1486,7 +1438,8 @@ void add_module_dis(VM* vm){
 
     vm->bind_func<1>(mod, "dis", [](VM* vm, ArgsView args) {
         CodeObject_ code = get_code(vm, args[0]);
-        vm->_stdout(vm, vm->disassemble(code));
+        Str msg = vm->disassemble(code);
+        vm->_stdout(vm, msg.data, msg.size);
         return vm->None;
     });
 
diff --git a/src/pocketpy_c.cpp b/src/pocketpy_c.cpp
index cb84836e..8ba2313d 100644
--- a/src/pocketpy_c.cpp
+++ b/src/pocketpy_c.cpp
@@ -569,6 +569,11 @@ void pkpy_compile_to_string(pkpy_vm* vm_handle, const char* source, const char*
     }
 }
 
+void pkpy_set_output_handler(pkpy_vm* vm_handle, pkpy_COutputHandler handler){
+    VM* vm = (VM*) vm_handle;
+    vm->_stdout = reinterpret_cast<PrintFunc>(handler);
+}
+
 void* pkpy_new_repl(pkpy_vm* vm_handle){
     return new REPL((VM*)vm_handle);
 }
diff --git a/src/repl.cpp b/src/repl.cpp
index d9b9033f..3ff64cbe 100644
--- a/src/repl.cpp
+++ b/src/repl.cpp
@@ -2,10 +2,10 @@
 
 namespace pkpy {
     REPL::REPL(VM* vm) : vm(vm){
-        vm->_stdout(vm, "pocketpy " PK_VERSION " (" __DATE__ ", " __TIME__ ") ");
-        vm->_stdout(vm, fmt("[", sizeof(void*)*8, " bit] on ", PK_SYS_PLATFORM "\n"));
-        vm->_stdout(vm, "https://github.com/blueloveTH/pocketpy" "\n");
-        vm->_stdout(vm, "Type \"exit()\" to exit." "\n");
+        vm->stdout_write("pocketpy " PK_VERSION " (" __DATE__ ", " __TIME__ ") ");
+        vm->stdout_write(fmt("[", sizeof(void*)*8, " bit] on ", PK_SYS_PLATFORM "\n"));
+        vm->stdout_write("https://github.com/blueloveTH/pocketpy" "\n");
+        vm->stdout_write("Type \"exit()\" to exit." "\n");
     }
 
     bool REPL::input(std::string line){
diff --git a/src/vm.cpp b/src/vm.cpp
index 062d4cce..a1c24759 100644
--- a/src/vm.cpp
+++ b/src/vm.cpp
@@ -5,13 +5,13 @@ namespace pkpy{
     VM::VM(bool enable_os) : heap(this), enable_os(enable_os) {
         this->vm = this;
         this->_c.error = nullptr;
-        _stdout = [](VM* vm, const Str& s) {
+        _stdout = [](VM* vm, const char* buf, int size) {
             PK_UNUSED(vm);
-            std::cout << s;
+            std::cout.write(buf, size);
         };
-        _stderr = [](VM* vm, const Str& s) {
+        _stderr = [](VM* vm, const char* buf, int size) {
             PK_UNUSED(vm);
-            std::cerr << s;
+            std::cerr.write(buf, size);
         };
         callstack.reserve(8);
         _main = nullptr;
@@ -99,13 +99,14 @@ namespace pkpy{
 #endif
             return _exec(code, _module);
         }catch (const Exception& e){
-            _stderr(this, e.summary() + "\n");
+            Str sum = e.summary() + "\n";
+            _stderr(this, sum.data, sum.size);
         }
 #if !PK_DEBUG_FULL_EXCEPTION
         catch (const std::exception& e) {
             Str msg = "An std::exception occurred! It could be a bug.\n";
-            msg = msg + e.what();
-            _stderr(this, msg + "\n");
+            msg = msg + e.what() + "\n";
+            _stderr(this, msg.data, msg.size);
         }
 #endif
         callstack.clear();
diff --git a/src2/pocketpy_c.c b/src2/pocketpy_c.c
index 97eb41ed..dbf6ed2b 100644
--- a/src2/pocketpy_c.c
+++ b/src2/pocketpy_c.c
@@ -237,6 +237,10 @@ void pkpy_compile_to_string(pkpy_vm* vm, const char* source, const char* filenam
 
 }
 
+void pkpy_set_output_handler(pkpy_vm* vm, pkpy_COutputHandler handler) {
+
+}
+
 void* pkpy_new_repl(pkpy_vm* vm) {
     void* returnValue;
     return returnValue;