diff --git a/include/pocketpy/interpreter/vm.h b/include/pocketpy/interpreter/vm.h
index a9bb2b8c..8fc4257b 100644
--- a/include/pocketpy/interpreter/vm.h
+++ b/include/pocketpy/interpreter/vm.h
@@ -41,9 +41,7 @@ typedef struct VM {
     py_TValue builtins;  // builtins module
     py_TValue main;      // __main__ module
 
-    void (*ceval_on_step)(Frame*, Bytecode);
-    char* (*import_file)(const char*);
-    void (*print)(const char*);
+    py_Callbacks callbacks;
 
     py_TValue last_retval;
     py_TValue curr_exception;
diff --git a/include/pocketpy/objects/codeobject.h b/include/pocketpy/objects/codeobject.h
index 949d0e86..220cb8cc 100644
--- a/include/pocketpy/objects/codeobject.h
+++ b/include/pocketpy/objects/codeobject.h
@@ -120,15 +120,6 @@ void FuncDecl__add_arg(FuncDecl* self, py_Name name);
 void FuncDecl__add_kwarg(FuncDecl* self, py_Name name, const py_TValue* value);
 void FuncDecl__add_starred_arg(FuncDecl* self, py_Name name);
 void FuncDecl__add_starred_kwarg(FuncDecl* self, py_Name name);
-FuncDecl_ FuncDecl__build(c11_sv name,
-                          c11_sv* args,
-                          int argc,
-                          c11_sv starred_arg,
-                          c11_sv* kwargs,
-                          int kwargc,
-                          py_Ref kwdefaults,  // a tuple contains default values
-                          c11_sv starred_kwarg,
-                          const char* docstring);
 
 // runtime function
 typedef struct Function {
diff --git a/include/pocketpy/pocketpy.h b/include/pocketpy/pocketpy.h
index dbcd6871..2a0a47a5 100644
--- a/include/pocketpy/pocketpy.h
+++ b/include/pocketpy/pocketpy.h
@@ -34,6 +34,14 @@ typedef struct c11_sv {
     int size;
 } c11_sv;
 
+/// A struct contains the callbacks of the VM.
+typedef struct py_Callbacks {
+    /// Used by `__import__` to load source code of a module.
+    char* (*importfile)(const char*);
+    /// Used by `print` to output a string.
+    void (*print)(const char*);
+} py_Callbacks;
+
 #define PY_RAISE
 #define PY_RETURN
 
@@ -84,6 +92,8 @@ PK_EXPORT int py_currentvm();
 PK_EXPORT void py_switchvm(int index);
 /// Set `sys.argv`. Used for storing command-line arguments.
 PK_EXPORT void py_sys_setargv(int argc, char** argv);
+/// Setup the callbacks for the current VM.
+PK_EXPORT py_Callbacks* py_callbacks();
 
 /// Run a source string.
 /// @param source source string.
diff --git a/src/interpreter/ceval.c b/src/interpreter/ceval.c
index 93c1ad87..142196db 100644
--- a/src/interpreter/ceval.c
+++ b/src/interpreter/ceval.c
@@ -120,8 +120,8 @@ FrameResult VM__run_top_frame(VM* self) {
                 if(TOP()->type != tp_NoneType) {
                     bool ok = py_repr(TOP());
                     if(!ok) goto __ERROR;
-                    self->print(py_tostr(&self->last_retval));
-                    self->print("\n");
+                    self->callbacks.print(py_tostr(&self->last_retval));
+                    self->callbacks.print("\n");
                 }
                 POP();
                 DISPATCH();
diff --git a/src/interpreter/vm.c b/src/interpreter/vm.c
index 06e59f89..08d4fb38 100644
--- a/src/interpreter/vm.c
+++ b/src/interpreter/vm.c
@@ -9,7 +9,7 @@
 #include "pocketpy/pocketpy.h"
 #include <stdbool.h>
 
-static char* pk_default_import_file(const char* path) {
+static char* pk_default_importfile(const char* path) {
 #if PK_ENABLE_OS
     FILE* f = fopen(path, "rb");
     if(f == NULL) return NULL;
@@ -61,9 +61,8 @@ void VM__ctor(VM* self) {
     self->builtins = *py_NIL;
     self->main = *py_NIL;
 
-    self->ceval_on_step = NULL;
-    self->import_file = pk_default_import_file;
-    self->print = pk_default_print;
+    self->callbacks.importfile = pk_default_importfile;
+    self->callbacks.print = pk_default_print;
 
     self->last_retval = *py_NIL;
     self->curr_exception = *py_NIL;
diff --git a/src/modules/dis.c b/src/modules/dis.c
index def8b0ed..7d1c936a 100644
--- a/src/modules/dis.c
+++ b/src/modules/dis.c
@@ -105,8 +105,8 @@ static void disassemble(CodeObject* co) {
     }
 
     c11_string* output = c11_sbuf__submit(&ss);
-    pk_current_vm->print(output->data);
-    pk_current_vm->print("\n");
+    pk_current_vm->callbacks.print(output->data);
+    pk_current_vm->callbacks.print("\n");
     c11_string__delete(output);
     c11_vector__dtor(&jumpTargets);
 }
diff --git a/src/public/internal.c b/src/public/internal.c
index e2b9bbcd..45817dab 100644
--- a/src/public/internal.c
+++ b/src/public/internal.c
@@ -76,6 +76,9 @@ void py_sys_setargv(int argc, char** argv) {
     }
 }
 
+py_Callbacks* py_getcallbacks() { return &pk_current_vm->callbacks; }
+
+
 const char* pk_opname(Opcode op) {
     const static char* OP_NAMES[] = {
 #define OPCODE(name) #name,
diff --git a/src/public/modules.c b/src/public/modules.c
index 5f58d4fa..d9d628f4 100644
--- a/src/public/modules.c
+++ b/src/public/modules.c
@@ -130,12 +130,12 @@ int py_import(const char* path_cstr) {
         goto __SUCCESS;
     }
 
-    data = vm->import_file(filename->data);
+    data = vm->callbacks.importfile(filename->data);
     if(data != NULL) goto __SUCCESS;
 
     c11_string__delete(filename);
     filename = c11_string__new3("%s/__init__.py", slashed_path->data);
-    data = vm->import_file(filename->data);
+    data = vm->callbacks.importfile(filename->data);
     if(data != NULL) goto __SUCCESS;
 
     c11_string__delete(filename);
@@ -290,7 +290,7 @@ static bool builtins_print(int argc, py_Ref argv) {
     }
     c11_sbuf__write_sv(&buf, end);
     c11_string* res = c11_sbuf__submit(&buf);
-    pk_current_vm->print(res->data);
+    pk_current_vm->callbacks.print(res->data);
     c11_string__delete(res);
     py_newnone(py_retval());
     return true;
diff --git a/src/public/py_exception.c b/src/public/py_exception.c
index 50b82c7e..f76fc4b0 100644
--- a/src/public/py_exception.c
+++ b/src/public/py_exception.c
@@ -160,8 +160,8 @@ void py_clearexc(py_StackRef p0) {
 void py_printexc() {
     char* msg = py_formatexc();
     if(!msg) return;
-    pk_current_vm->print(msg);
-    pk_current_vm->print("\n");
+    pk_current_vm->callbacks.print(msg);
+    pk_current_vm->callbacks.print("\n");
     free(msg);
 }