diff --git a/README.md b/README.md
index c408693..c4a383d 100644
--- a/README.md
+++ b/README.md
@@ -114,6 +114,14 @@ Or use this in __`linux/macOS/Unix`__
 
 > [cpp compiler] -std=c++11 -O3 main.cpp -o nasal -fno-exceptions -ldl
 
+Or using makefile,`mingw32-make` is __`Windows`__ platform's `make`:
+
+> mingw32-make nasal.exe
+
+in __`linux/macOS/Unix`__:
+
+> make nasal
+
 ## __How to Use__
 
 First we should learn how to write a program using this language,
@@ -1584,11 +1592,11 @@ vm stack(limit 5, total 0)
 If want help, input `h` to get help.
 
 ```bash
->> h
 <option>
         h,    help      | get help
         bt,   backtrace | get function call trace
         c,    continue  | run program until break point or exit
+        f,    file      | see all the compiled files
         g,    global    | see global values
         l,    local     | see local values
         u,    upval     | see upvalue
diff --git a/makefile b/makefile
index dcfcfcb..e7f9d92 100644
--- a/makefile
+++ b/makefile
@@ -1,6 +1,8 @@
 .PHONY=test
 nasal:main.cpp nasal_ast.h nasal_err.h nasal_builtin.h nasal_opt.h nasal_codegen.h nasal_gc.h nasal_import.h nasal_lexer.h nasal_parse.h nasal_vm.h nasal_dbg.h nasal.h
 	clang++ -std=c++11 -O3 main.cpp -o nasal -fno-exceptions -ldl -Wshadow -Wall
+nasal.exe:main.cpp nasal_ast.h nasal_err.h nasal_builtin.h nasal_opt.h nasal_codegen.h nasal_gc.h nasal_import.h nasal_lexer.h nasal_parse.h nasal_vm.h nasal_dbg.h nasal.h
+	g++ -std=c++11 -O3 main.cpp -o nasal.exe -fno-exceptions -Wshadow -Wall -static
 test:nasal
 	@ ./nasal -op -e test/ascii-art.nas
 	@ ./nasal -op -c test/bf.nas
diff --git a/nasal_gc.h b/nasal_gc.h
index d4dd90c..12eb9c0 100644
--- a/nasal_gc.h
+++ b/nasal_gc.h
@@ -166,6 +166,7 @@ struct nasal_obj
         if(destructor && ptr)
             {destructor(ptr);}
         ptr=nullptr;
+        destructor=nullptr;
     }
 };
 
diff --git a/test/tetris.nas b/test/tetris.nas
index 5cde440..a854d88 100644
--- a/test/tetris.nas
+++ b/test/tetris.nas
@@ -57,21 +57,16 @@ var blockshape=[
     [[0,0],[1,0],[0,1],[-1,1]]
 ];
 
-var stick_count=0; # make sure one stick in 10 tries
 var color_count=0;
-var last_type=-1;
-var typechange=func(t){
-    if(t==last_type)
-        t=int(rand()*size(blocktype));
-    if(t!=3){
-        stick_count+=1;
-        if(stick_count==8)
-            (t,stick_count)=(3,0);
-    }else
-        stick_count=0;
-    last_type=t;
-    return t;
+var counter=0;
+var package=[0,1,2,3,4,5,6];
+var exchange=func(){
+    for(var i=6;i>=0;i-=1){
+        var index=int(i*rand());
+        (package[i],package[index])=(package[index],package[i]);
+    }
 }
+
 var block={
     x:0,
     y:0,
@@ -82,9 +77,13 @@ var block={
     new:func(x=0,y=0){
         (me.x,me.y)=(x,y);
         me.rotate=0;
-        var t=typechange(int(rand()*size(blocktype)));
+        me.type=blocktype[package[counter]];
+        counter+=1;
+        if(counter==7){
+            exchange();
+            counter=0;
+        }
         
-        me.type=blocktype[t];
         me.shape=blockshape[me.type[me.rotate]];
 
         me.color=color_count;
@@ -293,7 +292,8 @@ var main=func(){
     );
 
     rand(time(0));
-    var map=mapgen(mapx:12,mapy:15);
+    exchange();
+    var map=mapgen(mapx:12,mapy:18);
 
     libkey.getch();
     print("\ec");