diff --git a/module/fib.cpp b/module/fib.cpp
index a65f8d6..b58ab8e 100644
--- a/module/fib.cpp
+++ b/module/fib.cpp
@@ -39,6 +39,6 @@ mod_func func_tbl[]={
     {nullptr, nullptr},
 };
 
-extern "C" mod_func* get() {
+extern "C" mod_func* get(ghost_register_table* table) {
     return func_tbl;
 }
\ No newline at end of file
diff --git a/module/keyboard.cpp b/module/keyboard.cpp
index 57f7f25..6736385 100644
--- a/module/keyboard.cpp
+++ b/module/keyboard.cpp
@@ -95,6 +95,6 @@ mod_func func_tbl[]={
     {nullptr,nullptr}
 };
 
-extern "C" mod_func* get() {
+extern "C" mod_func* get(ghost_register_table* table) {
     return func_tbl;
 }
\ No newline at end of file
diff --git a/module/matrix.cpp b/module/matrix.cpp
index 9166fdc..d74431c 100644
--- a/module/matrix.cpp
+++ b/module/matrix.cpp
@@ -291,6 +291,6 @@ mod_func func_tbl[]={
     {nullptr,nullptr}
 };
 
-extern "C" mod_func* get() {
+extern "C" mod_func* get(ghost_register_table* table) {
     return func_tbl;
 }
\ No newline at end of file
diff --git a/module/nasocket.cpp b/module/nasocket.cpp
index 3d4fa9b..3935567 100644
--- a/module/nasocket.cpp
+++ b/module/nasocket.cpp
@@ -206,6 +206,6 @@ mod_func func_tbl[]={
     {nullptr,nullptr}
 };
 
-extern "C" mod_func* get() {
+extern "C" mod_func* get(ghost_register_table* table) {
     return func_tbl;
 }
\ No newline at end of file
diff --git a/nasal_builtin.h b/nasal_builtin.h
index e36061b..a1c6c55 100644
--- a/nasal_builtin.h
+++ b/nasal_builtin.h
@@ -544,13 +544,13 @@ var builtin_open(var* local, gc& ngc) {
         return nas_err("open", "failed to open file <"+name.str()+">");
     }
     var ret=ngc.alloc(vm_obj);
-    ret.obj().set(obj_type::file, res);
+    ret.obj().set(ghost_file, res);
     return ret;
 }
 
 var builtin_close(var* local, gc& ngc) {
     var fd=local[1];
-    if (!fd.objchk(obj_type::file)) {
+    if (!fd.objchk(ghost_file)) {
         return nas_err("close", "not a valid filehandle");
     }
     fd.obj().clear();
@@ -561,7 +561,7 @@ var builtin_read(var* local, gc& ngc) {
     var fd=local[1];
     var buf=local[2];
     var len=local[3];
-    if (!fd.objchk(obj_type::file)) {
+    if (!fd.objchk(ghost_file)) {
         return nas_err("read", "not a valid filehandle");
     }
     if (buf.type!=vm_str || buf.val.gcobj->unmut) {
@@ -587,7 +587,7 @@ var builtin_read(var* local, gc& ngc) {
 var builtin_write(var* local, gc& ngc) {
     var fd=local[1];
     var str=local[2];
-    if (!fd.objchk(obj_type::file)) {
+    if (!fd.objchk(ghost_file)) {
         return nas_err("write", "not a valid filehandle");
     }
     if (str.type!=vm_str) {
@@ -600,7 +600,7 @@ var builtin_seek(var* local, gc& ngc) {
     var fd=local[1];
     var pos=local[2];
     var whence=local[3];
-    if (!fd.objchk(obj_type::file)) {
+    if (!fd.objchk(ghost_file)) {
         return nas_err("seek", "not a valid filehandle");
     }
     return var::num((f64)fseek((FILE*)fd.obj().ptr, pos.num(), whence.num()));
@@ -608,7 +608,7 @@ var builtin_seek(var* local, gc& ngc) {
 
 var builtin_tell(var* local, gc& ngc) {
     var fd=local[1];
-    if (!fd.objchk(obj_type::file)) {
+    if (!fd.objchk(ghost_file)) {
         return nas_err("tell", "not a valid filehandle");
     }
     return var::num((f64)ftell((FILE*)fd.obj().ptr));
@@ -616,7 +616,7 @@ var builtin_tell(var* local, gc& ngc) {
 
 var builtin_readln(var* local, gc& ngc) {
     var fd=local[1];
-    if (!fd.objchk(obj_type::file)) {
+    if (!fd.objchk(ghost_file)) {
         return nas_err("readln", "not a valid filehandle");
     }
     var str=ngc.alloc(vm_str);
@@ -664,7 +664,7 @@ var builtin_stat(var* local, gc& ngc) {
 
 var builtin_eof(var* local, gc& ngc) {
     var fd=local[1];
-    if (!fd.objchk(obj_type::file)) {
+    if (!fd.objchk(ghost_file)) {
         return nas_err("readln", "not a valid filehandle");
     }
     return var::num((f64)feof((FILE*)fd.obj().ptr));
@@ -849,13 +849,13 @@ var builtin_opendir(var* local, gc& ngc) {
     }
 #endif
     var ret=ngc.alloc(vm_obj);
-    ret.obj().set(obj_type::dir,p);
+    ret.obj().set(ghost_dir,p);
     return ret;
 }
 
 var builtin_readdir(var* local, gc& ngc) {
     var handle=local[1];
-    if (!handle.objchk(obj_type::dir)) {
+    if (!handle.objchk(ghost_dir)) {
         return nas_err("readdir", "not a valid dir handle");
     }
 #ifdef _MSC_VER
@@ -872,7 +872,7 @@ var builtin_readdir(var* local, gc& ngc) {
 
 var builtin_closedir(var* local, gc& ngc) {
     var handle=local[1];
-    if (!handle.objchk(obj_type::dir)) {
+    if (!handle.objchk(ghost_dir)) {
         return nas_err("closedir", "not a valid dir handle");
     }
     handle.obj().clear();
@@ -936,7 +936,7 @@ var builtin_dlopen(var* local, gc& ngc) {
     }
     var ret=ngc.temp=ngc.alloc(vm_hash);
     var lib=ngc.alloc(vm_obj);
-    lib.obj().set(obj_type::dylib, ptr);
+    lib.obj().set(ghost_dylib, ptr);
     ret.hash().elems["lib"]=lib;
 
 #ifdef _WIN32
@@ -948,14 +948,14 @@ var builtin_dlopen(var* local, gc& ngc) {
         return nas_err("dlopen", "cannot find <get> function");
     }
     // get function pointer by name
-    mod_func* tbl=(mod_func*)((getptr)func)();
+    mod_func* tbl=(mod_func*)((getptr)func)(&global_ghost_type_table);
     if (!tbl) {
         return nas_err("dlopen", "failed to get module functions");
     }
     for(u32 i=0;tbl[i].name;++i) {
         void* p=(void*)tbl[i].fd;
         var tmp=ngc.alloc(vm_obj);
-        tmp.obj().set(obj_type::faddr, p);
+        tmp.obj().set(ghost_faddr, p);
         ret.hash().elems[tbl[i].name]=tmp;
     }
 
@@ -965,7 +965,7 @@ var builtin_dlopen(var* local, gc& ngc) {
 
 var builtin_dlclose(var* local, gc& ngc) {
     var libptr=local[1];
-    if (!libptr.objchk(obj_type::dylib)) {
+    if (!libptr.objchk(ghost_dylib)) {
         return nas_err("dlclose", "\"lib\" is not a valid dynamic lib");
     }
     libptr.obj().clear();
@@ -975,7 +975,7 @@ var builtin_dlclose(var* local, gc& ngc) {
 var builtin_dlcallv(var* local, gc& ngc) {
     var fp=local[1];
     var args=local[2];
-    if (!fp.objchk(obj_type::faddr)) {
+    if (!fp.objchk(ghost_faddr)) {
         return nas_err("dlcall", "\"ptr\" is not a valid function pointer");
     }
     auto& vec=args.vec().elems;
@@ -984,7 +984,7 @@ var builtin_dlcallv(var* local, gc& ngc) {
 
 var builtin_dlcall(var* local, gc& ngc) {
     var fp=local[1];
-    if (!fp.objchk(obj_type::faddr)) {
+    if (!fp.objchk(ghost_faddr)) {
         return nas_err("dlcall", "\"ptr\" is not a valid function pointer");
     }
 
diff --git a/nasal_gc.h b/nasal_gc.h
index 0374e6b..63f37db 100644
--- a/nasal_gc.h
+++ b/nasal_gc.h
@@ -43,14 +43,6 @@ enum vm_type:u8 {
 
 const u32 gc_type_size=vm_co-vm_str+1;
 
-enum class obj_type:u32 {
-    null=0,
-    file=1,
-    dir,
-    dylib,
-    faddr
-};
-
 enum class coroutine_status:u32 {
     suspended,
     running,
@@ -99,7 +91,7 @@ public:
     // number and string can be translated to each other
     f64 tonum();
     string tostr();
-    bool objchk(obj_type);
+    bool objchk(usize);
 
     // create new var object
     static var none();
@@ -175,49 +167,76 @@ struct nas_upval {
     void clear() {onstk=true;elems.clear();size=0;}
 };
 
-struct ghost_info {
-    string name;
-    void (*destructor)(void*);
+void file_dtor(void* ptr) {
+    if ((FILE*)ptr==stdin) {
+        return;
+    }
+    fclose((FILE*)ptr);
+}
+
+void dir_dtor(void* ptr) {
+#ifndef _MSC_VER
+    closedir((DIR*)ptr);
+#else
+    FindClose(ptr);
+#endif
+}
+
+void dylib_dtor(void* ptr) {
+#ifdef _WIN32
+    FreeLibrary((HMODULE)ptr);
+#else
+    dlclose(ptr);
+#endif
+}
+
+void faddr_dtor(void* ptr) {}
+
+usize ghost_file, ghost_dir, ghost_dylib, ghost_faddr;
+
+struct ghost_register_table {
+private:
+    using dtor=void (*)(void*);
+
+private:
+    std::unordered_map<string,usize> mapper;
+    std::vector<dtor> destructors;
+
+public:
+    ghost_register_table() {
+        ghost_file=register_ghost_type("file", file_dtor);
+        ghost_dir=register_ghost_type("dir", dir_dtor);
+        ghost_dylib=register_ghost_type("dylib", dylib_dtor);
+        ghost_faddr=register_ghost_type("faddr", faddr_dtor);
+    }
+
+    usize register_ghost_type(const std::string& name, dtor ptr) {
+        if (mapper.count(name)) {
+            std::cerr<<"ghost type \""<<name<<"\" already exists.\n\n";
+            std::exit(-1);
+        }
+        auto res=destructors.size();
+        mapper[name]=res;
+        destructors.push_back(ptr);
+        return res;
+    }
+
+    dtor destructor(usize index) {
+        return destructors.at(index);
+    }
 };
 
-struct nas_ghost {
-private:
-    static std::vector<ghost_info> ghost_register_table;
+ghost_register_table global_ghost_type_table;
+
+struct nas_obj {
+public:
     usize type;
     void* ptr;
 
 public:
-    nas_ghost(): type(0), ptr(nullptr) {}
-    ~nas_ghost() {
-        if (!ptr) { return; }
-        ghost_register_table[type].destructor(ptr);
-    }
-
-    static usize regist_ghost_type(ghost_info i) {
-        auto res=ghost_register_table.size();
-        ghost_register_table.push_back(i);
-        return res;
-    }
-
-    const std::string& name() {
-        return ghost_register_table[type].name;
-    }
-};
-
-struct nas_obj {
-    obj_type type;
-    void* ptr;
-
-private:
-    /* RAII constructor, new object is initialized when creating */
-    void file_dtor();
-    void dir_dtor();
-    void dylib_dtor();
-
-public:
-    nas_obj(): type(obj_type::null), ptr(nullptr) {}
+    nas_obj(): type(0), ptr(nullptr) {}
     ~nas_obj() {clear();}
-    void set(obj_type, void*);
+    void set(usize, void*);
     void clear();
 };
 
@@ -357,47 +376,19 @@ void nas_func::clear() {
     keys.clear();
 }
 
-void nas_obj::set(obj_type t, void* p) {
+void nas_obj::set(usize t, void* p) {
     type=t;
     ptr=p;
 }
 
 void nas_obj::clear() {
-    if (!ptr) {
+    if (!ptr || !type) {
         return;
     }
-    switch(type) {
-        case obj_type::file:  file_dtor(); break;
-        case obj_type::dir:   dir_dtor();  break;
-        case obj_type::dylib: dylib_dtor();break;
-        default: break;
-    }
+    global_ghost_type_table.destructor(type)(ptr);
     ptr=nullptr;
 }
 
-void nas_obj::file_dtor() {
-    if ((FILE*)ptr==stdin) {
-        return;
-    }
-    fclose((FILE*)ptr);
-}
-
-void nas_obj::dir_dtor() {
-#ifndef _MSC_VER
-    closedir((DIR*)ptr);
-#else
-    FindClose(ptr);
-#endif
-}
-
-void nas_obj::dylib_dtor() {
-#ifdef _WIN32
-    FreeLibrary((HMODULE)ptr);
-#else
-    dlclose(ptr);
-#endif
-}
-
 void nas_co::clear() {
     for(u32 i=0;i<STACK_DEPTH;++i) {
         stack[i]=var::nil();
@@ -485,8 +476,8 @@ std::ostream& operator<<(std::ostream& out, var& ref) {
     return out;
 }
 
-bool var::objchk(obj_type objtype) {
-    return type==vm_obj && obj().type==objtype && obj().ptr;
+bool var::objchk(usize obj_type) {
+    return type==vm_obj && obj().type==obj_type && obj().ptr;
 }
 
 var var::none() {
@@ -884,4 +875,4 @@ struct mod_func {
 };
 
 // module function "get" type
-typedef mod_func* (*getptr)();
+typedef mod_func* (*getptr)(ghost_register_table*);
diff --git a/test/life.nas b/test/life.nas
index 73c458c..626d68c 100644
--- a/test/life.nas
+++ b/test/life.nas
@@ -11,7 +11,7 @@ var new_map=func(width,height){
 }
 
 var prt=func(map){
-    var s='\e[1;1H';
+    var s='\ec\e[1;1H';
     foreach(var line;map){
         foreach(var elem;line)
             s~=elem~' ';