diff --git a/README.md b/README.md
index 13eff3a..7db120a 100644
--- a/README.md
+++ b/README.md
@@ -142,7 +142,7 @@ Use these commands to get version of interpreter:
    /  \/ / _` / __|/ _` | |
   / /\  / (_| \__ \ (_| | |
   \_\ \/ \__,_|___/\__,_|_|
-nasal ver : 9.0
+nasal ver : 10.0
 c++ std   : 201103
 thanks to : https://github.com/andyross/nasal
 code repo : https://github.com/ValKmjolnir/Nasal-Interpreter
@@ -156,6 +156,9 @@ Use these commands to get help(see more debug commands in help):
 > ./nasal -h | --help
 
 ```bash
+     ,--#-,
+<3  / \____\  <3
+    |_|__A_|
 nasal <option>
 option:
     -h, --help    | get help.
@@ -633,7 +636,7 @@ nasal_ref builtin_keys(nasal_ref* local,nasal_gc& gc)
     if(hash.type!=vm_hash)
         return builtin_err("keys","\"hash\" must be hash");
     // push vector into local scope to avoid being sweeped
-    if(gc.top+1>=gc.stack+nasal_gc::stack_depth-1)
+    if(gc.top+1>=gc.canary)
         return builtin_err("keys","expand temporary space error:stackoverflow");
     (++gc.top)[0]=gc.alloc(vm_vec);
     auto& vec=gc.top[0].vec().elems;
diff --git a/main.cpp b/main.cpp
index 03a705d..94a622e 100644
--- a/main.cpp
+++ b/main.cpp
@@ -13,6 +13,9 @@ const uint32_t VM_OPTIMIZE =0x100;
 void help()
 {
     std::cout
+    <<"     ,--#-,\n"
+    <<"<3  / \\____\\  <3\n"
+    <<"    |_|__A_|\n"
 #ifdef _WIN32
     <<"use command <chcp 65001> if want to use unicode.\n"
 #endif
diff --git a/nasal.h b/nasal.h
index a84a197..520abd6 100644
--- a/nasal.h
+++ b/nasal.h
@@ -45,6 +45,8 @@
 #define PRTINT64   "%lld"
 #endif
 
+const uint32_t STACK_DEPTH=8192;
+
 inline double hex_to_double(const char* str)
 {
     double ret=0;
diff --git a/nasal_builtin.h b/nasal_builtin.h
index 2c23853..3445f1a 100644
--- a/nasal_builtin.h
+++ b/nasal_builtin.h
@@ -306,7 +306,7 @@ nasal_ref builtin_split(nasal_ref* local,nasal_gc& gc)
     size_t source_len=source.length();
 
     // push it to local scope to avoid being sweeped
-    if(gc.top+1>=gc.stack+nasal_gc::stack_depth-1)
+    if(gc.top+1>=gc.canary)
         return builtin_err("split","expand temporary space error:stackoverflow");
     (++gc.top)[0]=gc.alloc(vm_vec);
 
@@ -611,7 +611,7 @@ nasal_ref builtin_keys(nasal_ref* local,nasal_gc& gc)
     if(hash.type!=vm_hash)
         return builtin_err("keys","\"hash\" must be hash");
     // push vector into local scope to avoid being sweeped
-    if(gc.top+1>=gc.stack+nasal_gc::stack_depth-1)
+    if(gc.top+1>=gc.canary)
         return builtin_err("keys","expand temporary space error:stackoverflow");
     (++gc.top)[0]=gc.alloc(vm_vec);
     auto& vec=gc.top[0].vec().elems;
@@ -1115,7 +1115,7 @@ nasal_ref builtin_chdir(nasal_ref* local,nasal_gc& gc)
 nasal_ref builtin_environ(nasal_ref* local,nasal_gc& gc)
 {
     char** env=environ;
-    if(gc.top+1>=gc.stack+nasal_gc::stack_depth-1)
+    if(gc.top+1>=gc.canary)
         return builtin_err("environ","expand temporary space error:stackoverflow");
     (++gc.top)[0]=gc.alloc(vm_vec);
     auto& vec=gc.top[0].vec().elems;
diff --git a/nasal_codegen.h b/nasal_codegen.h
index 463f006..b600844 100644
--- a/nasal_codegen.h
+++ b/nasal_codegen.h
@@ -430,7 +430,7 @@ void nasal_codegen::func_gen(const nasal_ast& ast)
     block_gen(block);
     in_iterloop.pop();
     code[local_label].num=local.back().size();
-    if(local.back().size()>=nasal_gc::stack_depth)
+    if(local.back().size()>=STACK_DEPTH)
         die("too many local variants: "+std::to_string(local.back().size())+".",block.line());
     local.pop_back();
 
@@ -1232,7 +1232,7 @@ void nasal_codegen::compile(const nasal_parse& parse,const nasal_import& import)
     gen(op_intg,global.size(),0);
     block_gen(parse.ast()); // generate main block
     gen(op_exit,0,0);
-    if(global.size()>=nasal_gc::stack_depth)
+    if(global.size()>=STACK_DEPTH)
         die("too many global variants: "+std::to_string(global.size())+".",0);
     nerr.chkerr();
 }
diff --git a/nasal_gc.h b/nasal_gc.h
index 758ea0c..3e84c31 100644
--- a/nasal_gc.h
+++ b/nasal_gc.h
@@ -175,7 +175,7 @@ struct nasal_obj
     enum obj_type
     {
         null,
-        file=1,
+        file,
         dir,
         dylib,
         faddr
@@ -209,8 +209,7 @@ struct nasal_co
         running,
         dead
     };
-    static const uint32_t depth=1024;
-    nasal_ref  stack[depth];
+    nasal_ref  stack[STACK_DEPTH];
     
     uint32_t   pc;
     nasal_ref* top;
@@ -224,19 +223,19 @@ struct nasal_co
     nasal_co():
         pc(0),
         top(stack),
-        canary(stack+depth-1),
+        canary(stack+STACK_DEPTH-1),
         localr(nullptr),
         memr(nullptr),
         funcr({vm_nil,(double)0}),
         upvalr({vm_nil,(double)0}),
         status(nasal_co::suspended)
     {
-        for(uint32_t i=0;i<depth;++i)
+        for(uint32_t i=0;i<STACK_DEPTH;++i)
             stack[i]={vm_nil,(double)0};
     }
     void clear()
     {
-        for(uint32_t i=0;i<depth;++i)
+        for(uint32_t i=0;i<STACK_DEPTH;++i)
             stack[i]={vm_nil,(double)0};
         pc=0;
         localr=nullptr;
@@ -451,10 +450,8 @@ const nasal_ref nil ={vm_nil,(double)0};
 
 struct nasal_gc
 {
-    static const uint32_t   stack_depth=8192;        // depth of value stack
     struct
     {
-        nasal_ref  stack[stack_depth];
         uint32_t   pc;
         nasal_ref* top;
         nasal_ref* localr;
@@ -462,16 +459,17 @@ struct nasal_gc
         nasal_ref  funcr;
         nasal_ref  upvalr;
         nasal_ref* canary;
+        nasal_ref* stack;
     } main_ctx;
     
     /* runtime context */
-    uint32_t                pc;                      // program counter
-    nasal_ref*              top;                     // stack top
-    nasal_ref*              localr;                  // local scope register
-    nasal_ref*              memr;                    // used for mem_call
-    nasal_ref               funcr;                   // function register
-    nasal_ref               upvalr;                  // upvalue register
-    nasal_ref*              canary;                  // avoid stackoverflow
+    uint32_t&               pc;                      // program counter
+    nasal_ref*&             localr;                  // local scope register
+    nasal_ref*&             memr;                    // used for mem_call
+    nasal_ref&              funcr;                   // function register
+    nasal_ref&              upvalr;                  // upvalue register
+    nasal_ref*&             canary;                  // avoid stackoverflow
+    nasal_ref*&             top;                     // stack top
     nasal_ref*              stack;                   // stack pointer
     nasal_co*               coroutine;               // running coroutine
 
@@ -483,6 +481,23 @@ struct nasal_gc
     /* values for analysis */
     uint64_t                size[vm_type_size];
     uint64_t                count[vm_type_size];
+    nasal_gc(
+        uint32_t& _pc,
+        nasal_ref*& _localr,
+        nasal_ref*& _memr,
+        nasal_ref& _funcr,
+        nasal_ref& _upvalr,
+        nasal_ref*& _canary,
+        nasal_ref*& _top,
+        nasal_ref* _stk):
+        pc(_pc),
+        localr(_localr),
+        memr(_memr),
+        funcr(_funcr),
+        upvalr(_upvalr),
+        canary(_canary),
+        top(_top),
+        stack(_stk){}
     void                    mark();
     void                    sweep();
     void                    init(const std::vector<std::string>&);
@@ -499,6 +514,7 @@ void nasal_gc::mark()
 {
     std::queue<nasal_ref> bfs;
     
+    // this make sure values on main stack can be scanned
     if(!coroutine)
     {
         for(nasal_ref* i=stack;i<=top;++i)
@@ -585,9 +601,7 @@ void nasal_gc::init(const std::vector<std::string>& s)
             nasal_val* tmp=new nasal_val(i);
             memory.push_back(tmp);
             free_list[i].push(tmp);
-        } 
-    stack=main_ctx.stack;
-    top=main_ctx.stack;
+        }
     coroutine=nullptr;
     // init constant strings
     strs.resize(s.size());
@@ -679,6 +693,7 @@ void nasal_gc::ctxchg(nasal_co& context)
     main_ctx.funcr=funcr;
     main_ctx.upvalr=upvalr;
     main_ctx.canary=canary;
+    main_ctx.stack=stack;
 
     pc=context.pc;
     top=context.top;
@@ -694,24 +709,23 @@ void nasal_gc::ctxchg(nasal_co& context)
 }
 void nasal_gc::ctxreserve()
 {
-    if(coroutine->status!=nasal_co::dead)
-        coroutine->status=nasal_co::suspended;
-    // pc=0 means this coroutine is finished, so we use entry to reset it
-    coroutine->pc=pc==0?coroutine->funcr.func().entry:pc;
-    coroutine->top=top;
+    // pc=0 means this coroutine is finished
+    coroutine->status=pc?nasal_co::suspended:nasal_co::dead;
+    coroutine->pc=pc;
     coroutine->localr=localr;
     coroutine->memr=memr;
     coroutine->funcr=funcr;
     coroutine->upvalr=upvalr;
     coroutine->canary=canary;
+    coroutine->top=top;
 
     pc=main_ctx.pc;
-    top=main_ctx.top;
     localr=main_ctx.localr;
     memr=main_ctx.memr;
     funcr=main_ctx.funcr;
     upvalr=main_ctx.upvalr;
     canary=main_ctx.canary;
+    top=main_ctx.top;
     stack=main_ctx.stack;
     coroutine=nullptr;
 }
diff --git a/nasal_vm.h b/nasal_vm.h
index 8fac746..48cac59 100644
--- a/nasal_vm.h
+++ b/nasal_vm.h
@@ -5,24 +5,28 @@ class nasal_vm
 {
 protected:
     /* values of nasal_vm */
-    uint32_t&                pc;       // program counter
-    nasal_ref*               global;   // global scope register
-    nasal_ref*&              localr;   // local scope register
-    nasal_ref*&              memr;     // used for mem_call
-    nasal_ref&               funcr;    // function register
-    nasal_ref&               upvalr;   // upvalue register
-    nasal_ref*&              canary;   // avoid stackoverflow
-    nasal_ref*&              top;      // stack top
+    nasal_ref             stack[STACK_DEPTH];
+    uint32_t              pc;       // program counter
+    nasal_ref*            global;   // global scope register
+    nasal_ref*            localr;   // local scope register
+    nasal_ref*            memr;     // used for mem_call
+    nasal_ref             funcr;    // function register
+    nasal_ref             upvalr;   // upvalue register
+    nasal_ref*            canary;   // avoid stackoverflow
+    nasal_ref*            top;      // stack top
+
     /* constant */
-    const double*            num_table;// const numbers, ref from nasal_codegen
-    const std::string*       str_table;// const symbols, ref from nasal_codegen
-    std::vector<uint32_t>    imm;      // immediate number
+    const double*         num_table;// const numbers, ref from nasal_codegen
+    const std::string*    str_table;// const symbols, ref from nasal_codegen
+    std::vector<uint32_t> imm;      // immediate number
+
     /* garbage collector */
-    nasal_gc                 gc;
+    nasal_gc              gc;
+
     /* values used for debug */
-    size_t                   files_size;
-    const std::string*       files;    // ref from nasal_import
-    const opcode*            bytecode; // ref from nasal_codegen
+    size_t                files_size;
+    const std::string*    files;    // ref from nasal_import
+    const opcode*         bytecode; // ref from nasal_codegen
 
     void init(
         const std::vector<std::string>&,
@@ -121,14 +125,8 @@ protected:
     void opr_ret();
 public:
     nasal_vm():
-        pc(gc.pc),
-        global(gc.main_ctx.stack),
-        localr(gc.localr),
-        memr(gc.memr),
-        funcr(gc.funcr),
-        upvalr(gc.upvalr),
-        canary(gc.canary),
-        top(gc.top){}
+        global(stack),
+        gc(pc,localr,memr,funcr,upvalr,canary,top,stack){}
     void run(
         const nasal_codegen&,
         const nasal_import&,
@@ -148,13 +146,16 @@ void nasal_vm::init(
     bytecode=code.data();
     files=filenames.data();
     files_size=filenames.size();
+
     /* set canary and program counter */
-    canary=gc.stack+nasal_gc::stack_depth-1; // gc.stack[nasal_gc::stack_depth-1]
     pc=0;
+    global=stack;
     localr=nullptr;
     memr=nullptr;
     funcr=nil;
     upvalr=nil;
+    canary=stack+STACK_DEPTH-1; // stack[STACK_DEPTH-1]
+    top=stack;
 }
 void nasal_vm::valinfo(nasal_ref& val)
 {
@@ -237,9 +238,9 @@ void nasal_vm::bytecodeinfo(const char* header,const uint32_t p)
 }
 void nasal_vm::traceback()
 {
-    uint32_t global_size=bytecode[0].num; // bytecode[0] is op_intg
+    uint32_t   global_size=bytecode[0].num; // bytecode[0] is op_intg
     nasal_ref* t=top;
-    nasal_ref* bottom=gc.stack+global_size;
+    nasal_ref* bottom=stack+global_size;
     std::stack<uint32_t> ret;
     for(nasal_ref* i=bottom;i<=t;++i)
         if(i->type==vm_ret)
@@ -266,7 +267,7 @@ void nasal_vm::traceback()
 void nasal_vm::stackinfo(const uint32_t limit=10)
 {
     /* bytecode[0] is op_intg, the .num is the global size */
-    uint32_t   gsize=gc.stack==gc.main_ctx.stack?bytecode[0].num:0;
+    uint32_t   gsize=gc.stack==stack?bytecode[0].num:0;
     nasal_ref* t=top;
     nasal_ref* bottom=gc.stack+gsize;
     printf("vm stack(0x" PRTHEX64 "<sp+%u>, limit %u, total ",(uint64_t)bottom,gsize,limit);
@@ -285,7 +286,7 @@ void nasal_vm::stackinfo(const uint32_t limit=10)
 void nasal_vm::register_info()
 {
     printf("registers(%s):\n",gc.coroutine?"coroutine":"main");
-    printf("  [ pc     ]    | pc   | 0x%.x\n",pc);
+    printf("  [ pc     ]    | pc   | 0x%x\n",pc);
     printf("  [ global ]    | addr | 0x" PRTHEX64 "\n",(uint64_t)global);
     printf("  [ localr ]    | addr | 0x" PRTHEX64 "\n",(uint64_t)localr);
     printf("  [ memr   ]    | addr | 0x" PRTHEX64 "\n",(uint64_t)memr);
@@ -306,7 +307,7 @@ void nasal_vm::register_info()
 }
 void nasal_vm::global_state()
 {
-    if(!bytecode[0].num || gc.stack[0].type==vm_none) // bytecode[0].op is op_intg
+    if(!bytecode[0].num || stack[0].type==vm_none) // bytecode[0].op is op_intg
         return;
     printf("global(0x" PRTHEX64 "<sp+0>):\n",(uint64_t)global);
     for(uint32_t i=0;i<bytecode[0].num;++i)
@@ -955,26 +956,27 @@ inline void nasal_vm::opr_mcallh()
 }
 inline void nasal_vm::opr_ret()
 {
-    // +-----------------+
-    // | return value    | <- top[0]
-    // +-----------------+
-    // | old pc          | <- top[-1]
-    // +-----------------+
-    // | old localr      | <- top[-2]
-    // +-----------------+
-    // | old upvalr      | <- top[-3]
-    // +-----------------+
-    // | local scope     |
-    // | ...             |
-    // +-----------------+ <- local pointer stored in localr
-    // | old funcr       | <- old function stored in funcr
-    // +-----------------+
-    nasal_ref  ret=top[0];
+/*  +-----------------+
+*   | return value    | <- top[0]
+*   +-----------------+
+*   | old pc          | <- top[-1]
+*   +-----------------+
+*   | old localr      | <- top[-2]
+*   +-----------------+
+*   | old upvalr      | <- top[-3]
+*   +-----------------+
+*   | local scope     |
+*   | ...             |
+*   +-----------------+ <- local pointer stored in localr
+*   | old funcr       | <- old function stored in funcr
+*   +-----------------+
+*/
+    nasal_ref  ret  =top[0];
     nasal_ref* local=localr;
-    nasal_ref  func=funcr;
-    nasal_ref  up=upvalr;
+    nasal_ref  func =funcr;
+    nasal_ref  up   =upvalr;
 
-    pc=top[-1].ret();
+    pc    =top[-1].ret();
     localr=top[-2].addr();
     upvalr=top[-3];
 
@@ -992,11 +994,10 @@ inline void nasal_vm::opr_ret()
         for(uint32_t i=0;i<size;++i)
             upval.elems.push_back(local[i]);
     }
-    if(!pc) // cannot use gc.coroutine to judge, because there maybe another function call inside
-    {
-        gc.coroutine->status=nasal_co::dead;
+    // cannot use gc.coroutine to judge,
+    // because there maybe another function call inside
+    if(!pc)
         gc.ctxreserve();
-    }
 }
 void nasal_vm::run(
     const nasal_codegen& gen,