diff --git a/nasal.h b/nasal.h
index 0c2ebfd..041fed3 100644
--- a/nasal.h
+++ b/nasal.h
@@ -132,7 +132,7 @@ f64 str2num(const char* str)
     return negative?-res:res;
 }
 
-int utf8_hdchk(const char head)
+i32 utf8_hdchk(const char head)
 {
     // RFC-2279 but now we use RFC-3629 so nbytes is less than 4
     const u8 c=(u8)head;
diff --git a/nasal_builtin.h b/nasal_builtin.h
index 4810305..e0c5a55 100644
--- a/nasal_builtin.h
+++ b/nasal_builtin.h
@@ -356,7 +356,7 @@ nas_ref builtin_rand(nas_ref* local,nasal_gc& gc)
         return builtin_err("rand","\"seed\" must be nil or number");
     if(val.type==vm_num)
     {
-        srand((unsigned int)val.num());
+        srand((u32)val.num());
         return nil;
     }
     f64 num=0;
@@ -662,10 +662,9 @@ nas_ref builtin_left(nas_ref* local,nasal_gc& gc)
         return builtin_err("left","\"string\" must be string");
     if(len.type!=vm_num)
         return builtin_err("left","\"length\" must be number");
-    int length=(int)len.num();
-    if(length<0)
-        length=0;
-    return gc.newstr(str.str().substr(0,length));
+    if(len.num()<0)
+        return gc.newstr("");
+    return gc.newstr(str.str().substr(0,len.num()));
 }
 nas_ref builtin_right(nas_ref* local,nasal_gc& gc)
 {
@@ -675,13 +674,13 @@ nas_ref builtin_right(nas_ref* local,nasal_gc& gc)
         return builtin_err("right","\"string\" must be string");
     if(len.type!=vm_num)
         return builtin_err("right","\"length\" must be number");
-    int length=(int)len.num();
-    int srclen=str.str().length();
+    i32 length=(i32)len.num();
+    i32 srclen=str.str().length();
     if(length>srclen)
         length=srclen;
     if(length<0)
         length=0;
-    return gc.newstr(str.str().substr(srclen-length, srclen));
+    return gc.newstr(str.str().substr(srclen-length,srclen));
 }
 nas_ref builtin_cmp(nas_ref* local,nasal_gc& gc)
 {
@@ -716,7 +715,7 @@ nas_ref builtin_chr(nas_ref* local,nasal_gc& gc)
     nas_ref code=local[1];
     if(code.type!=vm_num)
         return builtin_err("chr","\"code\" must be number");
-    int num=code.num();
+    i32 num=code.num();
     if(0<=num && num<128)
         return gc.newstr((char)num);
     else if(128<=num && num<256)
@@ -974,7 +973,7 @@ nas_ref builtin_sleep(nas_ref* local,nasal_gc& gc)
 nas_ref builtin_pipe(nas_ref* local,nasal_gc& gc)
 {
 #ifndef _WIN32
-    int fd[2];
+    i32 fd[2];
     nas_ref res=gc.alloc(vm_vec);
     if(pipe(fd)==-1)
         return builtin_err("pipe","failed to create pipe");
@@ -1001,8 +1000,8 @@ nas_ref builtin_waitpid(nas_ref* local,nasal_gc& gc)
     if(pid.type!=vm_num || nohang.type!=vm_num)
         return builtin_err("waitpid","pid and nohang must be number");
 #ifndef _WIN32
-    int ret_pid;
-    int status;
+    i32 ret_pid;
+    i32 status;
     ret_pid=waitpid(pid.num(),&status,nohang.num()==0?0:WNOHANG);
     nas_ref vec=gc.alloc(vm_vec);
     vec.vec().elems.push_back({vm_num,(f64)ret_pid});
diff --git a/nasal_codegen.h b/nasal_codegen.h
index 49bf78d..d10fea4 100644
--- a/nasal_codegen.h
+++ b/nasal_codegen.h
@@ -1,7 +1,7 @@
 #ifndef __NASAL_CODEGEN_H__
 #define __NASAL_CODEGEN_H__
 
-enum op_code
+enum op_code:u8
 {
     op_exit,   // stop the virtual machine
     op_intg,   // global scope size
@@ -82,7 +82,7 @@ enum op_code
 
 struct
 {
-    int type;
+    u8 type;
     const char* name;
 }code_table[]=
 {
@@ -160,8 +160,7 @@ struct
     {op_mupval,"mupval"},
     {op_mcallv,"mcallv"},
     {op_mcallh,"mcallh"},
-    {op_ret,   "ret   "},
-    {-1,       nullptr },
+    {op_ret,   "ret   "}
 };
 
 struct opcode
@@ -253,12 +252,12 @@ private:
     std::vector<f64> num_res;
     std::vector<string> str_res;
     std::vector<opcode> code;
-    std::list<std::vector<int>> continue_ptr;
-    std::list<std::vector<int>> break_ptr;
+    std::list<std::vector<i32>> continue_ptr;
+    std::list<std::vector<i32>> break_ptr;
     // global : max 4095 values
-    std::unordered_map<string,int> global;
+    std::unordered_map<string,i32> global;
     // local  : max 32768 upvalues 65536 values
-    std::list<std::unordered_map<string,int>> local;
+    std::list<std::unordered_map<string,i32>> local;
 
     // func end stack, reserved for code print
     std::stack<u32> fbstk;
@@ -269,9 +268,9 @@ private:
     void regist_str(const string&);
     void find_symbol(const nasal_ast&);
     void add_sym(const string&);
-    int  local_find(const string&);
-    int  global_find(const string&);
-    int  upvalue_find(const string&);
+    i32  local_find(const string&);
+    i32  global_find(const string&);
+    i32  upvalue_find(const string&);
     void gen(u8,u32,u32);
     void num_gen(const nasal_ast&);
     void str_gen(const nasal_ast&);
@@ -293,7 +292,7 @@ private:
     void multi_assign_gen(const nasal_ast&);
     void conditional_gen(const nasal_ast&);
     void loop_gen(const nasal_ast&);
-    void load_continue_break(int,int);
+    void load_continue_break(i32,i32);
     void while_gen(const nasal_ast&);
     void for_gen(const nasal_ast&);
     void forindex_gen(const nasal_ast&);
@@ -372,32 +371,32 @@ void nasal_codegen::add_sym(const string& name)
     {
         if(global.count(name))
             return;
-        int index=global.size();
+        i32 index=global.size();
         global[name]=index;
         return;
     }
     if(local.back().count(name))
         return;
-    int index=local.back().size();
+    i32 index=local.back().size();
     local.back()[name]=index;
 }
 
-int nasal_codegen::local_find(const string& name)
+i32 nasal_codegen::local_find(const string& name)
 {
     if(local.empty())
         return -1;
     return local.back().count(name)?local.back()[name]:-1;
 }
 
-int nasal_codegen::global_find(const string& name)
+i32 nasal_codegen::global_find(const string& name)
 {
     return global.count(name)?global[name]:-1;
 }
 
-int nasal_codegen::upvalue_find(const string& name)
+i32 nasal_codegen::upvalue_find(const string& name)
 {
     // 32768 level 65536 upvalues
-    int index=-1;
+    i32 index=-1;
     usize size=local.size();
     if(size<=1)
         return -1;
@@ -530,7 +529,7 @@ void nasal_codegen::call_id(const nasal_ast& ast)
                 die("builtin functions work in a local scope.",ast.line());
             return;
         }
-    int index;
+    i32 index;
     if((index=local_find(str))>=0)
     {
         gen(op_calll,index,ast.line());
@@ -646,7 +645,7 @@ void nasal_codegen::mcall_id(const nasal_ast& ast)
             die("cannot change builtin function.",ast.line());
             return;
         }
-    int index;
+    i32 index;
     if((index=local_find(str))>=0)
     {
         gen(op_mcalll,index,ast.line());
@@ -723,12 +722,12 @@ void nasal_codegen::def_gen(const nasal_ast& ast)
 
 void nasal_codegen::multi_assign_gen(const nasal_ast& ast)
 {
-    int size=ast[0].size();
+    i32 size=ast[0].size();
     if(ast[1].type()==ast_multi_scalar)
     {
-        for(int i=size-1;i>=0;--i)
+        for(i32 i=size-1;i>=0;--i)
             calc_gen(ast[1][i]);
-        for(int i=0;i<size;++i)
+        for(i32 i=0;i<size;++i)
         {
             mcall(ast[0][i]);
             // multi assign user loadl and loadg to avoid meq's stack--
@@ -746,7 +745,7 @@ void nasal_codegen::multi_assign_gen(const nasal_ast& ast)
     else
     {
         calc_gen(ast[1]);
-        for(int i=0;i<size;++i)
+        for(i32 i=0;i<size;++i)
         {
             gen(op_callvi,i,ast[1].line());
             // multi assign user loadl and loadg to avoid meq's stack--
@@ -767,7 +766,7 @@ void nasal_codegen::multi_assign_gen(const nasal_ast& ast)
 
 void nasal_codegen::conditional_gen(const nasal_ast& ast)
 {
-    std::vector<int> jmp_label;
+    std::vector<usize> jmp_label;
     for(auto& tmp:ast.child())
     {
         if(tmp.type()==ast_if || tmp.type()==ast_elsif)
@@ -796,8 +795,8 @@ void nasal_codegen::conditional_gen(const nasal_ast& ast)
 
 void nasal_codegen::loop_gen(const nasal_ast& ast)
 {
-    continue_ptr.push_front(std::vector<int>());
-    break_ptr.push_front(std::vector<int>());
+    continue_ptr.push_front(std::vector<i32>());
+    break_ptr.push_front(std::vector<i32>());
     switch(ast.type())
     {
         case ast_while:   while_gen(ast);   break;
@@ -807,7 +806,7 @@ void nasal_codegen::loop_gen(const nasal_ast& ast)
     }
 }
 
-void nasal_codegen::load_continue_break(int continue_place,int break_place)
+void nasal_codegen::load_continue_break(i32 continue_place,i32 break_place)
 {
     for(auto i:continue_ptr.front())
         code[i].num=continue_place;
diff --git a/nasal_dbg.h b/nasal_dbg.h
index e04f7d2..96f63a8 100644
--- a/nasal_dbg.h
+++ b/nasal_dbg.h
@@ -192,7 +192,7 @@ void nasal_dbg::interact()
                 std::cout<<"cannot find file named `"<<res[1]<<"`\n";
                 bk_fidx=0;
             }
-            int tmp=atoi(res[2].c_str());
+            i32 tmp=atoi(res[2].c_str());
             if(tmp<=0)
                 std::cout<<"incorrect line number `"<<res[2]<<"`\n";
             else
diff --git a/nasal_err.h b/nasal_err.h
index 7041b1f..8726e71 100644
--- a/nasal_err.h
+++ b/nasal_err.h
@@ -56,7 +56,7 @@ public:
         ++error;
         const string& code=res[line-1];
         std::cerr<<"["<<stage<<"] "<<file<<":"<<line<<":"<<column<<" "<<info<<"\n"<<code<<"\n";
-        for(int i=0;i<(int)column-1;++i)
+        for(i32 i=0;i<(i32)column-1;++i)
             std::cerr<<char(" \t"[code[i]=='\t']);
         std::cerr<<"^\n";
     }
diff --git a/nasal_gc.h b/nasal_gc.h
index 4c7c44a..5e5e7e3 100644
--- a/nasal_gc.h
+++ b/nasal_gc.h
@@ -104,8 +104,8 @@ struct nas_vec
     nas_vec():printed(false){}
     void     print();
     usize    size(){return elems.size();}
-    nas_ref  get_val(const int);
-    nas_ref* get_mem(const int);
+    nas_ref  get_val(const i32);
+    nas_ref* get_mem(const i32);
 };
 
 struct nas_hash
@@ -249,19 +249,19 @@ struct nas_val
     ~nas_val();
 };
 
-nas_ref nas_vec::get_val(const int index)
+nas_ref nas_vec::get_val(const i32 n)
 {
-    int size=elems.size();
-    if(index<-size || index>=size)
+    i32 size=elems.size();
+    if(n<-size || n>=size)
         return {vm_none};
-    return elems[index>=0?index:index+size];
+    return elems[n>=0?n:n+size];
 }
-nas_ref* nas_vec::get_mem(const int index)
+nas_ref* nas_vec::get_mem(const i32 n)
 {
-    int size=elems.size();
-    if(index<-size || index>=size)
+    i32 size=elems.size();
+    if(n<-size || n>=size)
         return nullptr;
-    return &elems[index>=0?index:index+size];
+    return &elems[n>=0?n:n+size];
 }
 void nas_vec::print()
 {
diff --git a/nasal_parse.h b/nasal_parse.h
index 1822fd7..ce48687 100644
--- a/nasal_parse.h
+++ b/nasal_parse.h
@@ -123,7 +123,7 @@ void nasal_parse::compile(const nasal_lexer& lexer)
 }
 void nasal_parse::die(u32 line,string info,bool report_prev=false)
 {
-    int col=(int)tokens[ptr].col-(tokens[ptr].type==tok_eof?0:(int)tokens[ptr].str.length());
+    i32 col=(i32)tokens[ptr].col-(tokens[ptr].type==tok_eof?0:(i32)tokens[ptr].str.length());
     if(tokens[ptr].type==tok_str)
         col-=2; // tok_str's str has no \"
     if(report_prev && ptr) // used to report lack of ',' ';'
diff --git a/nasal_vm.h b/nasal_vm.h
index 0e46537..e383d71 100644
--- a/nasal_vm.h
+++ b/nasal_vm.h
@@ -640,8 +640,8 @@ inline void nasal_vm::o_callv()
     else if(vec.type==vm_str)
     {
         string& str=vec.str();
-        int num=val.tonum();
-        int len=str.length();
+        i32 num=val.tonum();
+        i32 len=str.length();
         if(num<-len || num>=len)
             die("callv: index out of range:"+std::to_string(val.tonum()));
         top[0]={vm_num,f64((u8)str[num>=0? num:num+len])};
@@ -802,9 +802,9 @@ inline void nasal_vm::o_slc2()
     std::vector<nas_ref>& aim=top[0].vec().elems;
 
     u8 type1=val1.type,type2=val2.type;
-    int num1=val1.tonum();
-    int num2=val2.tonum();
-    int size=ref.size();
+    i32 num1=val1.tonum();
+    i32 num2=val2.tonum();
+    i32 size=ref.size();
     if(type1==vm_nil && type2==vm_nil)
     {
         num1=0;
@@ -822,7 +822,7 @@ inline void nasal_vm::o_slc2()
     else if(num2<-size || num2>=size)
         die("slc2: end index out of range: "+std::to_string(num2));
     else
-        for(int i=num1;i<=num2;++i)
+        for(i32 i=num1;i<=num2;++i)
             aim.push_back(i>=0?ref[i]:ref[i+size]);
 }
 inline void nasal_vm::o_mcallg()