diff --git a/README.md b/README.md
index f8120da..fcf580d 100644
--- a/README.md
+++ b/README.md
@@ -296,7 +296,7 @@ Check built-in functions in lib.nas!
 
 If you want to add your own built-in functions,define the function in nasal_builtin.h.
 
-definition:
+Definition:
 
 ```C++
 nasal_val* builtin_chr(nasal_val*,nasal_gc&);
diff --git a/main.cpp b/main.cpp
index cba161a..fea031b 100644
--- a/main.cpp
+++ b/main.cpp
@@ -9,25 +9,27 @@ nasal_vm       vm;
 
 void help()
 {
-	std::cout<<">> [\"file\"] input a file name.\n";
-	std::cout<<">> [help  ] show help.\n";
-	std::cout<<">> [clear ] clear the screen.\n";
-	std::cout<<">> [lex   ] use lexer to turn code into tokens.\n";
-	std::cout<<">> [ast   ] do parsing and check the abstract syntax tree.\n";
-	std::cout<<">> [code  ] show byte code.\n";
-	std::cout<<">> [exec  ] execute program on bytecode vm.\n";
-	std::cout<<">> [logo  ] print logo of nasal .\n";
-	std::cout<<">> [exit  ] quit nasal interpreter.\n";
+	std::cout
+	<<">> [\"file\"] input a file name.\n"
+	<<">> [help  ] show help.\n"
+	<<">> [clear ] clear the screen.\n"
+	<<">> [lex   ] use lexer to turn code into tokens.\n"
+	<<">> [ast   ] do parsing and check the abstract syntax tree.\n"
+	<<">> [code  ] show byte code.\n"
+	<<">> [exec  ] execute program on bytecode vm.\n"
+	<<">> [logo  ] print logo of nasal .\n"
+	<<">> [exit  ] quit nasal interpreter.\n";
 	return;
 }
 
 void logo()
 {
-    std::cout<<"       __                _      \n";
-	std::cout<<"    /\\ \\ \\__ _ ___  __ _| |  \n";
-	std::cout<<"   /  \\/ / _` / __|/ _` | |    \n";
-	std::cout<<"  / /\\  / (_| \\__ \\ (_| | |  \n";
-	std::cout<<"  \\_\\ \\/ \\__,_|___/\\__,_|_|\n";
+    std::cout
+	<<"       __                _      \n"
+	<<"    /\\ \\ \\__ _ ___  __ _| |  \n"
+	<<"   /  \\/ / _` / __|/ _` | |    \n"
+	<<"  / /\\  / (_| \\__ \\ (_| | |  \n"
+	<<"  \\_\\ \\/ \\__,_|___/\\__,_|_|\n";
     return;
 }
 
diff --git a/nasal.h b/nasal.h
index e29f444..ccd55c3 100644
--- a/nasal.h
+++ b/nasal.h
@@ -19,7 +19,7 @@
 #include <stack>
 #include <queue>
 #include <vector>
-#include <map>
+#include <unordered_map>
 
 /*
 	check if a string can be converted to a number
diff --git a/nasal_builtin.h b/nasal_builtin.h
index 6b8362f..21b4c68 100644
--- a/nasal_builtin.h
+++ b/nasal_builtin.h
@@ -9,7 +9,7 @@
 // }
 // builtin function nasal_call_builtin_std_cout is wrapped up by print
 
-std::map<std::string,int> builtin_use_string_table;
+std::unordered_map<std::string,int> builtin_use_string_table;
 // used to find values that builtin function uses
 #define in_builtin_find(value_name_string) \
 (\
diff --git a/nasal_codegen.h b/nasal_codegen.h
index 9837c5d..1a7553d 100644
--- a/nasal_codegen.h
+++ b/nasal_codegen.h
@@ -128,8 +128,8 @@ struct opcode
 class nasal_codegen
 {
 private:
-    std::map<double,int>         number_table;
-    std::map<std::string,int>    string_table;
+    std::unordered_map<double,int>      number_table;
+    std::unordered_map<std::string,int> string_table;
     std::vector<double>          number_result_table;
     std::vector<std::string>     string_result_table;
     std::vector<opcode>          exec_code;
@@ -918,9 +918,9 @@ void nasal_codegen::main_progress(nasal_ast& ast)
     gen(op_nop,0);
     number_result_table.resize(number_table.size());
     string_result_table.resize(string_table.size());
-    for(std::map<double,int>::iterator i=number_table.begin();i!=number_table.end();++i)
+    for(auto i=number_table.begin();i!=number_table.end();++i)
         number_result_table[i->second]=i->first;
-    for(std::map<std::string,int>::iterator i=string_table.begin();i!=string_table.end();++i)
+    for(auto i=string_table.begin();i!=string_table.end();++i)
         string_result_table[i->second]=i->first;
     return;
 }
diff --git a/nasal_gc.h b/nasal_gc.h
index 3679b05..d2f3e9f 100644
--- a/nasal_gc.h
+++ b/nasal_gc.h
@@ -40,7 +40,7 @@ class nasal_hash
 {
 private:
     nasal_gc& gc;
-    std::map<std::string,nasal_val*> elems;
+    std::unordered_map<std::string,nasal_val*> elems;
 public:
     nasal_hash(nasal_gc&);
     ~nasal_hash();
@@ -82,7 +82,7 @@ class nasal_scop
 {
 private:
     nasal_gc& gc;
-    std::map<int,nasal_val*> elems;
+    std::unordered_map<int,nasal_val*> elems;
 public:
     nasal_scop(nasal_gc&);
     ~nasal_scop();
@@ -133,7 +133,6 @@ private:
 public:
     ~nasal_gc();
     void clear();
-    void debug();
     nasal_val* gc_alloc(int);
     void add_reference(nasal_val*);
     void del_reference(nasal_val*);
@@ -226,20 +225,20 @@ nasal_hash::nasal_hash(nasal_gc& ngc):gc(ngc)
 }
 nasal_hash::~nasal_hash()
 {
-    for(std::map<std::string,nasal_val*>::iterator iter=elems.begin();iter!=elems.end();++iter)
+    for(auto iter=elems.begin();iter!=elems.end();++iter)
         gc.del_reference(iter->second);
     elems.clear();
     return;
 }
 void nasal_hash::add_elem(std::string key,nasal_val* value_address)
 {
-    if(elems.find(key)==elems.end())
+    if(!elems.count(key))
         elems[key]=value_address;
     return;
 }
 void nasal_hash::del_elem(std::string key)
 {
-    if(elems.find(key)!=elems.end())
+    if(!elems.count(key))
     {
         gc.del_reference(elems[key]);
         elems.erase(key);
@@ -252,16 +251,16 @@ int nasal_hash::size()
 }
 nasal_val* nasal_hash::get_special_para(std::string key)
 {
-    if(elems.find(key)!=elems.end())
+    if(elems.count(key))
         return elems[key];
     return NULL;
 }
 nasal_val* nasal_hash::get_value_address(std::string key)
 {
     nasal_val* ret_value_addr=NULL;
-    if(elems.find(key)!=elems.end())
+    if(elems.count(key))
         return elems[key];
-    else if(elems.find("parents")!=elems.end())
+    else if(elems.count("parents"))
     {
         nasal_val* val_addr=elems["parents"];
         if(val_addr->get_type()==vm_vec)
@@ -283,9 +282,9 @@ nasal_val* nasal_hash::get_value_address(std::string key)
 nasal_val** nasal_hash::get_mem_address(std::string key)
 {
     nasal_val** mem_addr=NULL;
-    if(elems.find(key)!=elems.end())
+    if(elems.count(key))
         return &elems[key];
-    else if(elems.find("parents")!=elems.end())
+    else if(elems.count("parents"))
     {
         nasal_val* val_addr=elems["parents"];
         if(val_addr->get_type()==vm_vec)
@@ -306,9 +305,9 @@ nasal_val** nasal_hash::get_mem_address(std::string key)
 }
 bool nasal_hash::check_contain(std::string key)
 {
-    if(elems.find(key)!=elems.end())
+    if(elems.count(key))
         return true;
-    if(elems.find("parents")!=elems.end())
+    if(elems.count("parents"))
     {
         bool result=false;
         nasal_val* val_addr=elems["parents"];
@@ -333,7 +332,7 @@ nasal_val* nasal_hash::get_keys()
 {
     nasal_val* ret_addr=gc.gc_alloc(vm_vec);
     nasal_vec& ref_vec=ret_addr->get_vector();
-    for(std::map<std::string,nasal_val*>::iterator iter=elems.begin();iter!=elems.end();++iter)
+    for(auto iter=elems.begin();iter!=elems.end();++iter)
     {
         nasal_val* str_addr=gc.gc_alloc(vm_str);
         str_addr->set_string(iter->first);
@@ -343,12 +342,15 @@ nasal_val* nasal_hash::get_keys()
 }
 void nasal_hash::print()
 {
-    std::cout<<"{";
+    std::cout<<'{';
     if(!elems.size())
-        std::cout<<"}";
-    for(std::map<std::string,nasal_val*>::iterator i=elems.begin();i!=elems.end();++i)
     {
-        std::cout<<i->first<<":";
+        std::cout<<'}';
+        return;
+    }
+    for(auto i=elems.begin();i!=elems.end();++i)
+    {
+        std::cout<<i->first<<':';
         nasal_val* tmp=i->second;
         switch(tmp->get_type())
         {
@@ -359,9 +361,9 @@ void nasal_hash::print()
             case vm_hash: tmp->get_hash().print();      break;
             case vm_func: std::cout<<"func(...){...}";  break;
         }
-        std::cout<<",}"[(++i)==elems.end()];
-        --i;
+        std::cout<<',';
     }
+    std::cout<<'}';
     return;
 }
 
@@ -437,14 +439,14 @@ nasal_scop::nasal_scop(nasal_gc& ngc):gc(ngc)
 }
 nasal_scop::~nasal_scop()
 {
-    for(std::map<int,nasal_val*>::iterator i=elems.begin();i!=elems.end();++i)
+    for(auto i=elems.begin();i!=elems.end();++i)
         gc.del_reference(i->second);
     elems.clear();
     return;
 }
 void nasal_scop::add_new_value(int key,nasal_val* value_address)
 {
-    if(elems.find(key)!=elems.end())
+    if(elems.count(key))
     {
         // if this value already exists,delete the old value and update a new value
         gc.del_reference(elems[key]);
@@ -454,22 +456,22 @@ void nasal_scop::add_new_value(int key,nasal_val* value_address)
 }
 nasal_val* nasal_scop::get_value_address(int key)
 {
-    if(elems.find(key)!=elems.end())
+    if(elems.count(key))
         return elems[key];
     return NULL;
 }
 nasal_val** nasal_scop::get_mem_address(int key)
 {
-    if(elems.find(key)!=elems.end())
+    if(elems.count(key))
         return &(elems[key]);
     return NULL;
 }
 void nasal_scop::set_closure(nasal_scop& tmp)
 {
-    for(std::map<int,nasal_val*>::iterator i=elems.begin();i!=elems.end();++i)
+    for(auto i=elems.begin();i!=elems.end();++i)
         gc.del_reference(i->second);
     elems=tmp.elems;
-    for(std::map<int,nasal_val*>::iterator i=elems.begin();i!=elems.end();++i)
+    for(auto i=elems.begin();i!=elems.end();++i)
         gc.add_reference(i->second);
     return;
 }
@@ -566,13 +568,10 @@ int nasal_val::get_type()
 }
 double nasal_val::to_number()
 {
-    switch(type)
-    {
-        case vm_nil: return 0;
-        case vm_num: return ptr.num;
-        case vm_str: return trans_string_to_number(*ptr.str);
-        default:     return std::nan("");
-    }
+    if(type==vm_num)
+        return ptr.num;
+    else if(type==vm_str)
+        return trans_string_to_number(*ptr.str);
     return 0;
 }
 double nasal_val::get_number()
@@ -581,12 +580,10 @@ double nasal_val::get_number()
 }
 std::string nasal_val::to_string()
 {
-    switch(type)
-    {
-        case vm_num:return trans_number_to_string(ptr.num);
-        case vm_str:return *ptr.str;
-        default:return "";
-    }
+    if(type==vm_str)
+        return *ptr.str;
+    else if(type==vm_num)
+        return trans_number_to_string(ptr.num);
     return "";
 }
 std::string nasal_val::get_string()
@@ -623,27 +620,6 @@ nasal_gc::~nasal_gc()
     memory.clear();
     return;
 }
-void nasal_gc::debug()
-{
-    int gc_mem_size=memory.size();
-    for(int i=0;i<gc_mem_size;++i)
-        if(memory[i]->ref_cnt)
-        {
-            std::cout<<">> [debug] "<<i<<": "<<memory[i]->ref_cnt<<" ";
-            switch(memory[i]->get_type())
-            {
-                case vm_nil:std::cout<<"nil";break;
-                case vm_num:std::cout<<"number "<<memory[i]->get_number();break;
-                case vm_str:std::cout<<"string "<<memory[i]->get_string();break;
-                case vm_vec:std::cout<<"vector";break;
-                case vm_hash:std::cout<<"hash";break;
-                case vm_func:std::cout<<"function";break;
-                case vm_scop:std::cout<<"closure";break;
-            }
-            std::cout<<"\n";
-        }
-    return;
-}
 void nasal_gc::clear()
 {
     int gc_mem_size=memory.size();
diff --git a/nasal_parse.h b/nasal_parse.h
index 8f5acd9..b1acf9a 100644
--- a/nasal_parse.h
+++ b/nasal_parse.h
@@ -449,7 +449,7 @@ nasal_ast nasal_parse::args_gen()
         if(checked_dynamic_ids && i!=node_child_size-1)
             die(node.get_children()[i].get_line(),"dynamic identifier must be the end of argument list: "+args_format);
     }
-    std::map<std::string,bool> argname_table;
+    std::unordered_map<std::string,bool> argname_table;
     for(int i=0;i<node_child_size;++i)
     {
         std::string new_name;
diff --git a/nasal_vm.h b/nasal_vm.h
index 799866f..c7a9f80 100644
--- a/nasal_vm.h
+++ b/nasal_vm.h
@@ -1,18 +1,18 @@
 #ifndef __NASAL_VM_H__
 #define __NASAL_VM_H__
-#define val_stack_MAX_DEPTH 8192
+#define STACK_MAX_DEPTH 8192
 
 class nasal_vm
 {
 private:
-    bool main_loop_break_mark;
-    int ptr;      // program counter
-    int me_index; // this is the index of "me" in string_table
-    nasal_val* global_scope_addr;
-    // garbage collector and memory manager
-    nasal_gc gc;
-    // byte codes store here
-    std::vector<opcode> exec_code;
+    nasal_val* zero_addr;          // reserved address of nasal_val,type vm_num, 0
+    nasal_val* one_addr;           // reserved address of nasal_val,type vm_num, 1
+    bool main_loop_break_mark;     // when mark is false,break the main loop
+    int ptr;                       // program counter
+    int me_index;                  // this is the index of "me" in string_table
+    nasal_val* global_scope_addr;  // global scope address,type vm_scop
+    nasal_gc gc;                   // garbage collector and memory manager
+    std::vector<opcode> exec_code; // byte codes store here
     // main calculation stack
     nasal_val** val_stack;
     nasal_val** val_stack_top;
@@ -26,9 +26,7 @@ private:
     std::stack<int> call_stack;
     // iterator stack for forindex/foreach
     std::stack<int> counter_stack;
-    // string table
     std::vector<std::string> string_table;
-    // number table
     std::vector<double> number_table;
     void die(std::string);
     bool check_condition(nasal_val*);
@@ -98,7 +96,7 @@ public:
 
 nasal_vm::nasal_vm()
 {
-    val_stack=new nasal_val*[val_stack_MAX_DEPTH];
+    val_stack=new nasal_val*[STACK_MAX_DEPTH];
     val_stack_top=val_stack;
     local_scope_stack.push(NULL);
     return;
@@ -139,14 +137,14 @@ bool nasal_vm::check_condition(nasal_val* value_addr)
 {
     int type=value_addr->get_type();
     if(type==vm_num)
-        return (value_addr->get_number()!=0);
+        return value_addr->get_number();
     else if(type==vm_str)
     {
         std::string str=value_addr->get_string();
         double number=trans_string_to_number(str);
         if(std::isnan(number))
-            return str.length()!=0;
-        return (number!=0);
+            return str.length();
+        return number;
     }
     return false;
 }
@@ -172,16 +170,14 @@ void nasal_vm::opr_pushnum()
 }
 void nasal_vm::opr_pushone()
 {
-    nasal_val* val_addr=gc.gc_alloc(vm_num);
-    val_addr->set_number(1);
-    *(++val_stack_top)=val_addr;
+    *(++val_stack_top)=one_addr;
+    gc.add_reference(one_addr);
     return;
 }
 void nasal_vm::opr_pushzero()
 {
-    nasal_val* val_addr=gc.gc_alloc(vm_num);
-    val_addr->set_number(0);
-    *(++val_stack_top)=val_addr;
+    *(++val_stack_top)=zero_addr;
+    gc.add_reference(zero_addr);
     return;
 }
 void nasal_vm::opr_pushnil()
@@ -691,15 +687,17 @@ void nasal_vm::opr_foreach()
 void nasal_vm::opr_call()
 {
     nasal_val* val_addr=NULL;
-    int name_index=exec_code[ptr].index;
     nasal_val* local_scope_top=local_scope_stack.top();
+    int name_index=exec_code[ptr].index;
     if(local_scope_top)
-        val_addr=local_scope_top->get_closure().get_value_address(name_index);
-    if(val_addr)
     {
-        gc.add_reference(val_addr);
-        *(++val_stack_top)=val_addr;
-        return;
+        val_addr=local_scope_top->get_closure().get_value_address(name_index);
+        if(val_addr)
+        {
+            gc.add_reference(val_addr);
+            *(++val_stack_top)=val_addr;
+            return;
+        }
     }
     val_addr=global_scope_addr->get_closure().get_value_address(name_index);
     if(val_addr)
@@ -1097,6 +1095,10 @@ void nasal_vm::run(std::vector<std::string>& strs,std::vector<double>& nums,std:
     string_table=strs;
     number_table=nums;
     exec_code=exec;
+    zero_addr=gc.gc_alloc(vm_num);
+    zero_addr->set_number(0);
+    one_addr=gc.gc_alloc(vm_num);
+    one_addr->set_number(1);
     builtin_use_string_table.clear();
     for(int i=0;i<string_table.size();++i)
     {