diff --git a/nasal_codegen.h b/nasal_codegen.h
index d45e58f..618737a 100644
--- a/nasal_codegen.h
+++ b/nasal_codegen.h
@@ -3,7 +3,7 @@
 
 enum op_code
 {
-    op_nop,     // do nothing
+    op_exit,    // stop the virtual machine
     op_intg,    // global scope size
     op_intl,    // local scope size
     op_loadg,   // load global value
@@ -77,8 +77,7 @@ enum op_code
     op_mupval,  // get memory space of value in closure
     op_mcallv,  // get memory space of vec[index]
     op_mcallh,  // get memory space of hash.label
-    op_ret,     // return
-    op_exit     // stop the virtual machine
+    op_ret      // return
 };
 
 struct
@@ -87,7 +86,7 @@ struct
     const char* name;
 }code_table[]=
 {
-    {op_nop,     "nop   "},
+    {op_exit,    "exit  "},
     {op_intg,    "intg  "},
     {op_intl,    "intl  "},
     {op_loadg,   "loadg "},
@@ -162,7 +161,6 @@ struct
     {op_mcallv,  "mcallv"},
     {op_mcallh,  "mcallh"},
     {op_ret,     "ret   "},
-    {op_exit,    "exit  "},
     {-1,         nullptr },
 };
 
@@ -172,7 +170,7 @@ struct opcode
     uint16_t fidx;// source code file index
     uint32_t num; // imm num
     uint32_t line;// line of source code
-    opcode(uint8_t o=op_nop,uint16_t f=0,uint32_t n=0,uint32_t l=0):
+    opcode(uint8_t o=op_exit,uint16_t f=0,uint32_t n=0,uint32_t l=0):
         op(o),fidx(f),num(n),line(l){}
     opcode& operator=(const opcode& tmp)
     {
diff --git a/nasal_dbg.h b/nasal_dbg.h
index 3b1e8b7..7f9f1a9 100644
--- a/nasal_dbg.h
+++ b/nasal_dbg.h
@@ -105,7 +105,7 @@ void nasal_dbg::interact()
         <<"[debug] nasal debug mode\n"
         <<"input \'h\' to get help\n";
     }
-    else if(bytecode[pc].op==op_nop || bytecode[pc].op==op_exit)
+    else if(bytecode[pc].op==op_exit)
         return;
     
     if(
@@ -183,7 +183,7 @@ void nasal_dbg::run(
     init(gen.get_strs(),gen.get_nums(),gen.get_code(),linker.get_file());
     const void* opr_table[]=
     {
-        &&nop,     &&intg,     &&intl,   &&loadg,
+        &&vmexit,  &&intg,     &&intl,   &&loadg,
         &&loadl,   &&loadu,    &&pnum,   &&pnil,
         &&pstr,    &&newv,     &&newh,   &&newf,
         &&happ,    &&para,     &&defpara,&&dynpara,
@@ -201,7 +201,7 @@ void nasal_dbg::run(
         &&callvi,  &&callh,    &&callfv, &&callfh,
         &&callb,   &&slcbegin, &&slcend, &&slc,
         &&slc2,    &&mcallg,   &&mcalll, &&mupval,
-        &&mcallv,  &&mcallh,   &&ret,    &&vmexit
+        &&mcallv,  &&mcallh,   &&ret
     };
     std::vector<const void*> code;
     for(auto& i:gen.get_code())
@@ -221,7 +221,6 @@ vmexit:
     return;
 #define dbg(op) {interact();op();if(gc.top<canary)goto *code[++pc];goto vmexit;}
 
-nop:     dbg(opr_nop     );
 intg:    dbg(opr_intg    );
 intl:    dbg(opr_intl    );
 loadg:   dbg(opr_loadg   );
diff --git a/nasal_gc.h b/nasal_gc.h
index 94028f7..b09e535 100644
--- a/nasal_gc.h
+++ b/nasal_gc.h
@@ -87,8 +87,10 @@ struct nasal_ref
 
 struct nasal_vec
 {
+    uint32_t depth;
     std::vector<nasal_ref> elems;
 
+    nasal_vec():depth(0){}
     void       print();
     nasal_ref  get_val(const int);
     nasal_ref* get_mem(const int);
@@ -96,8 +98,10 @@ struct nasal_vec
 
 struct nasal_hash
 {
+    uint32_t depth;
     std::unordered_map<std::string,nasal_ref> elems;
 
+    nasal_hash():depth(0){}
     void       print();
     nasal_ref  get_val(const std::string&);
     nasal_ref* get_mem(const std::string&);
@@ -174,8 +178,7 @@ nasal_ref* nasal_vec::get_mem(const int index)
 }
 void nasal_vec::print()
 {
-    static int depth=0;
-    if(!elems.size() || depth>8)
+    if(!elems.size() || depth>3)
     {
         std::cout<<(elems.size()?"[..]":"[]");
         return;
@@ -231,8 +234,7 @@ nasal_ref* nasal_hash::get_mem(const std::string& key)
 }
 void nasal_hash::print()
 {
-    static int depth=0;
-    if(!elems.size() || depth>8)
+    if(!elems.size() || depth>3)
     {
         std::cout<<(elems.size()?"{..}":"{}");
         return;
diff --git a/nasal_vm.h b/nasal_vm.h
index 0e96d21..59c28a1 100644
--- a/nasal_vm.h
+++ b/nasal_vm.h
@@ -41,7 +41,6 @@ protected:
     /* vm calculation functions*/
     bool condition(nasal_ref);
     /* vm operands */
-    void opr_nop();
     void opr_intg();
     void opr_intl();
     void opr_loadg();
@@ -322,7 +321,6 @@ inline bool nasal_vm::condition(nasal_ref val)
     }
     return false;
 }
-inline void nasal_vm::opr_nop(){}
 inline void nasal_vm::opr_intg()
 {
     // global values store on stack
@@ -883,10 +881,10 @@ void nasal_vm::run(
 {
     detail_info=detail;
     init(gen.get_strs(),gen.get_nums(),gen.get_code(),linker.get_file());
-    uint64_t count[op_exit+1]={0};
+    uint64_t count[op_ret+1]={0};
     const void* opr_table[]=
     {
-        &&nop,     &&intg,     &&intl,   &&loadg,
+        &&vmexit,  &&intg,     &&intl,   &&loadg,
         &&loadl,   &&loadu,    &&pnum,   &&pnil,
         &&pstr,    &&newv,     &&newh,   &&newf,
         &&happ,    &&para,     &&defpara,&&dynpara,
@@ -904,7 +902,7 @@ void nasal_vm::run(
         &&callvi,  &&callh,    &&callfv, &&callfh,
         &&callb,   &&slcbegin, &&slcend, &&slc,
         &&slc2,    &&mcallg,   &&mcalll, &&mupval,
-        &&mcallv,  &&mcallh,   &&ret,    &&vmexit
+        &&mcallv,  &&mcallh,   &&ret
     };
     std::vector<const void*> code;
     for(auto& i:gen.get_code())
@@ -930,7 +928,6 @@ vmexit:
 // do not cause stackoverflow
 #define exec_opnodie(op,num) {op();++count[num];goto *code[++pc];}
 
-nop:     exec_opnodie(opr_nop     ,op_nop     ); // 0
 intg:    exec_opnodie(opr_intg    ,op_intg    ); // +imm[pc] (detected at codegen)
 intl:    exec_opnodie(opr_intl    ,op_intl    ); // -0
 loadg:   exec_opnodie(opr_loadg   ,op_loadg   ); // -1
diff --git a/test/ascii-art.nas b/test/ascii-art.nas
index 94714ad..1b087e0 100644
--- a/test/ascii-art.nas
+++ b/test/ascii-art.nas
@@ -116,6 +116,7 @@ var curve4=func()
 }
 trans_ttf("just for test");
 trans_ttf(" ValKmjolnir ");
+trans_ttf("just for fun");
 curve1();
 curve2();
 curve3();