diff --git a/lib.nas b/lib.nas
index f10a161..9a5f952 100644
--- a/lib.nas
+++ b/lib.nas
@@ -284,6 +284,7 @@ var unix=
 };
 
 # dylib is the core hashmap for developers to load their own library.
+# for safe using dynamic library, you could use 'module' in stl/module.nas
 var dylib=
 {
     # open dynamic lib.
diff --git a/module/fib.cpp b/module/fib.cpp
index 9728b74..a3e2b53 100644
--- a/module/fib.cpp
+++ b/module/fib.cpp
@@ -8,6 +8,8 @@ double fibonaci(double x){
 }
 extern "C" nasal_ref fib(std::vector<nasal_ref>& args,nasal_gc& gc){
     std::cout<<"[mod] this is the first test module of nasal\n";
+    if(!args.size())
+        return builtin_err("fib","lack arguments");
     nasal_ref num=args[0];
     if(num.type!=vm_num)
         return builtin_err("extern_fib","\"num\" must be number");
@@ -15,6 +17,8 @@ extern "C" nasal_ref fib(std::vector<nasal_ref>& args,nasal_gc& gc){
 }
 extern "C" nasal_ref quick_fib(std::vector<nasal_ref>& args,nasal_gc& gc){
     std::cout<<"[mod] this is the first test module of nasal\n";
+    if(!args.size())
+        return builtin_err("fib","lack arguments");
     nasal_ref num=args[0];
     if(num.type!=vm_num)
         return builtin_err("extern_quick_fib","\"num\" must be number");
diff --git a/nasal_builtin.h b/nasal_builtin.h
index 50f7b24..7004fc9 100644
--- a/nasal_builtin.h
+++ b/nasal_builtin.h
@@ -5,6 +5,7 @@
 #include <crt_externs.h>
 #define environ (*_NSGetEnviron())
 #endif
+
 /*
     builtin functions must be called inside a function like this:
     var print=func(elems...){
diff --git a/nasal_gc.h b/nasal_gc.h
index 3193922..1a7fe3a 100644
--- a/nasal_gc.h
+++ b/nasal_gc.h
@@ -137,8 +137,16 @@ struct nasal_obj
 {
     uint32_t type;
     void* ptr;
-    nasal_obj():ptr(nullptr){}
-    void clear(){ptr=nullptr;}
+    void* destructor;
+    nasal_obj():ptr(nullptr),destructor(nullptr){}
+    ~nasal_obj(){clear();}
+    void clear()
+    {
+        typedef void (*func)(void*);
+        if(destructor)
+            (func(destructor))(ptr);
+        ptr=nullptr;
+    }
 };
 
 const uint8_t GC_UNCOLLECTED=0;   
diff --git a/stl/lib.nas b/stl/lib.nas
index f10a161..9a5f952 100644
--- a/stl/lib.nas
+++ b/stl/lib.nas
@@ -284,6 +284,7 @@ var unix=
 };
 
 # dylib is the core hashmap for developers to load their own library.
+# for safe using dynamic library, you could use 'module' in stl/module.nas
 var dylib=
 {
     # open dynamic lib.
diff --git a/stl/module.nas b/stl/module.nas
new file mode 100644
index 0000000..e6c8636
--- /dev/null
+++ b/stl/module.nas
@@ -0,0 +1,45 @@
+# lib module.nas
+# ValKmjolnir 2022/3/5
+
+# this provides safe usage of dylib
+# when dylib is closed,
+# all the invalid functions cannot be called
+import("lib.nas");
+
+var module_call_func=func(fptr,args){
+    return __builtin_dlcall;
+}
+var extern={
+    new: func(fptr){
+        return {
+            fptr:fptr,
+            isopen:1,
+            parents:[extern]
+        };
+    },
+    call: func(args...){
+        return (!me.isopen)?nil:module_call_func(me.fptr,args);
+    }
+};
+var module={
+    new: func(name){
+        return {
+            name:name,
+            lib:dylib.dlopen(name),
+            f:{},
+            parents:[module]
+        };
+    },
+    get: func(symbol){
+        if(contains(me.f,symbol))
+            return me.f[symbol];
+        var f=extern.new(dylib.dlsym(me.lib,symbol));
+        me.f[symbol]=f;
+        return f;
+    },
+    close: func(){
+        foreach(var i;keys(me.f))
+            me.f[i].isopen=0;
+        dylib.dlclose(me.lib);
+    }
+};
\ No newline at end of file