diff --git a/main.cpp b/main.cpp
index e442544..0e7a508 100644
--- a/main.cpp
+++ b/main.cpp
@@ -8,6 +8,7 @@ constexpr uint32_t VM_OPCALLNUM=16;
 constexpr uint32_t VM_EXEC     =32;
 constexpr uint32_t VM_DBGINFO  =64;
 constexpr uint32_t VM_DEBUG    =128;
+constexpr uint32_t VM_OPTIMIZE =256;
 
 void help()
 {
@@ -24,13 +25,14 @@ void help()
     <<"    input file name to execute script file.\n\n"
     <<"nasal [options...] <file>\n"
     <<"option:\n"
-    <<"    -l,   --lex   | view token info.\n"
-    <<"    -a,   --ast   | view abstract syntax tree.\n"
-    <<"    -c,   --code  | view bytecode.\n"
-    <<"    -t,   --time  | execute and get the running time.\n"
-    <<"    -o,   --opcnt | execute and count used operands.\n"
-    <<"    -d,   --detail| execute and get detail crash info.\n"
-    <<"    -dbg, --debug | debug mode (this will ignore -t -o -d).\n"
+    <<"    -l,   --lex     | view token info.\n"
+    <<"    -a,   --ast     | view abstract syntax tree.\n"
+    <<"    -c,   --code    | view bytecode.\n"
+    <<"    -t,   --time    | execute and get the running time.\n"
+    <<"    -o,   --opcnt   | execute and count used operands.\n"
+    <<"    -d,   --detail  | execute and get detail crash info.\n"
+    <<"    -op,  --optimize| use optimizer(beta).\n"
+    <<"    -dbg, --debug   | debug mode (this will ignore -t -o -d).\n"
     <<"file:\n"
     <<"    input file name to execute script file.\n";
 }
@@ -82,8 +84,11 @@ void execute(const std::string& file,const uint32_t cmd)
     if(cmd&VM_ASTINFO)
         parse.print();
     
+    // optimizer does simple optimization on ast
+    if(cmd&VM_OPTIMIZE)
+        optimize(parse.ast());
+    
     // code generator gets parser's ast and linker's import file list to generate code
-    optimize(parse.ast());
     gen.compile(parse,linker);
     if(cmd&VM_CODEINFO)
         gen.print();
@@ -140,6 +145,8 @@ int main(int argc,const char* argv[])
             cmd|=VM_EXECTIME;
         else if(s=="--detail" || s=="-d")
             cmd|=VM_DBGINFO|VM_EXEC;
+        else if(s=="--optimize" || s=="-op")
+            cmd|=VM_OPTIMIZE;
         else if(s=="--debug" || s=="-dbg")
             cmd|=VM_DEBUG;
         else
diff --git a/nasal_codegen.h b/nasal_codegen.h
index af59796..4e55786 100644
--- a/nasal_codegen.h
+++ b/nasal_codegen.h
@@ -10,8 +10,6 @@ enum op_code
     op_loadl,   // load local value
     op_loadu,   // load upvalue
     op_pnum,    // push constant number to the stack
-    op_pone,    // push 1 to the stack
-    op_pzero,   // push 0 to the stack
     op_pnil,    // push constant nil to the stack
     op_pstr,    // push constant string to the stack
     op_newv,    // push new vector with initial values from stack
@@ -96,8 +94,6 @@ struct
     {op_loadl,   "loadl "},
     {op_loadu,   "loadu "},
     {op_pnum,    "pnum  "},
-    {op_pone,    "pone  "},
-    {op_pzero,   "pzero "},
     {op_pnil,    "pnil  "},
     {op_pstr,    "pstr  "},
     {op_newv,    "newv  "},
@@ -363,13 +359,8 @@ void nasal_codegen::gen(uint8_t op,uint32_t num,uint32_t line)
 void nasal_codegen::num_gen(const nasal_ast& ast)
 {
     double num=ast.num();
-    if(num==0)gen(op_pzero,0,ast.line());
-    else if(num==1)gen(op_pone,0,ast.line());
-    else
-    {
-        regist_number(num);
-        gen(op_pnum,num_table[num],ast.line());
-    }
+    regist_number(num);
+    gen(op_pnum,num_table[num],ast.line());
 }
 
 void nasal_codegen::str_gen(const nasal_ast& ast)
@@ -816,7 +807,7 @@ void nasal_codegen::for_gen(const nasal_ast& ast)
     }
     int jmp_place=code.size();
     if(ast[1].type()==ast_null)
-        gen(op_pone,0,ast[1].line());
+        gen(op_pnum,num_table[1],ast[1].line());
     else
         calc_gen(ast[1]);
     int label_exit=code.size();
@@ -1150,6 +1141,9 @@ void nasal_codegen::compile(const nasal_parse& parse,const nasal_import& import)
     file=import.get_file().data();
     in_iterloop.push(0);
 
+    regist_number(0);
+    regist_number(1);
+
     find_symbol(parse.ast()); // search symbols first
     gen(op_intg,global.size(),0);
     block_gen(parse.ast()); // generate main block
diff --git a/nasal_dbg.h b/nasal_dbg.h
index 031121a..2b72da3 100644
--- a/nasal_dbg.h
+++ b/nasal_dbg.h
@@ -184,25 +184,24 @@ void nasal_dbg::run(
     const void* opr_table[]=
     {
         &&nop,     &&intg,     &&intl,   &&loadg,
-        &&loadl,   &&loadu,    &&pnum,   &&pone,
-        &&pzero,   &&pnil,     &&pstr,   &&newv,
-        &&newh,    &&newf,     &&happ,   &&para,
-        &&defpara, &&dynpara,  &&unot,   &&usub,
-        &&add,     &&sub,      &&mul,    &&div,
-        &&lnk,     &&addc,     &&subc,   &&mulc,
-        &&divc,    &&lnkc,     &&addeq,  &&subeq,
-        &&muleq,   &&diveq,    &&lnkeq,  &&addeqc,
-        &&subeqc,  &&muleqc,   &&diveqc, &&lnkeqc,
-        &&meq,     &&eq,       &&neq,    &&less,
-        &&leq,     &&grt,      &&geq,    &&lessc,
-        &&leqc,    &&grtc,     &&geqc,   &&pop,
-        &&jmp,     &&jt,       &&jf,     &&counter,
-        &&findex,  &&feach,    &&callg,  &&calll,
-        &&upval,   &&callv,    &&callvi, &&callh,
-        &&callfv,  &&callfh,   &&callb,  &&slcbegin,
-        &&slcend,  &&slc,      &&slc2,   &&mcallg,
-        &&mcalll,  &&mupval,   &&mcallv, &&mcallh,
-        &&ret,     &&vmexit
+        &&loadl,   &&loadu,    &&pnum,   &&pnil,
+        &&pstr,    &&newv,     &&newh,   &&newf,
+        &&happ,    &&para,     &&defpara,&&dynpara,
+        &&unot,    &&usub,     &&add,    &&sub,
+        &&mul,     &&div,      &&lnk,    &&addc,
+        &&subc,    &&mulc,     &&divc,   &&lnkc,
+        &&addeq,   &&subeq,    &&muleq,  &&diveq,
+        &&lnkeq,   &&addeqc,   &&subeqc, &&muleqc,
+        &&diveqc,  &&lnkeqc,   &&meq,    &&eq,
+        &&neq,     &&less,     &&leq,    &&grt,
+        &&geq,     &&lessc,    &&leqc,   &&grtc,
+        &&geqc,    &&pop,      &&jmp,    &&jt,
+        &&jf,      &&counter,  &&findex, &&feach,
+        &&callg,   &&calll,    &&upval,  &&callv,
+        &&callvi,  &&callh,    &&callfv, &&callfh,
+        &&callb,   &&slcbegin, &&slcend, &&slc,
+        &&slc2,    &&mcallg,   &&mcalll, &&mupval,
+        &&mcallv,  &&mcallh,   &&ret,    &&vmexit
     };
     bytecode=gen.get_code().data();
     std::vector<const void*> code;
@@ -234,8 +233,6 @@ loadg:   dbg(opr_loadg   );
 loadl:   dbg(opr_loadl   );
 loadu:   dbg(opr_loadu   );
 pnum:    dbg(opr_pnum    );
-pone:    dbg(opr_pone    );
-pzero:   dbg(opr_pzero   );
 pnil:    dbg(opr_pnil    );
 pstr:    dbg(opr_pstr    );
 newv:    dbg(opr_newv    );
diff --git a/nasal_vm.h b/nasal_vm.h
index 3d9bff9..e676f54 100644
--- a/nasal_vm.h
+++ b/nasal_vm.h
@@ -44,8 +44,6 @@ protected:
     void opr_loadl();
     void opr_loadu();
     void opr_pnum();
-    void opr_pone();
-    void opr_pzero();
     void opr_pnil();
     void opr_pstr();
     void opr_newv();
@@ -343,14 +341,6 @@ inline void nasal_vm::opr_pnum()
 {
     (++gc.top)[0]={vm_num,num_table[imm[pc]]};
 }
-inline void nasal_vm::opr_pone()
-{
-    (++gc.top)[0]={vm_num,(double)1};
-}
-inline void nasal_vm::opr_pzero()
-{
-    (++gc.top)[0]={vm_num,(double)0};
-}
 inline void nasal_vm::opr_pnil()
 {
     (++gc.top)[0]={vm_nil,(double)0};
@@ -858,25 +848,24 @@ void nasal_vm::run(
     const void* opr_table[]=
     {
         &&nop,     &&intg,     &&intl,   &&loadg,
-        &&loadl,   &&loadu,    &&pnum,   &&pone,
-        &&pzero,   &&pnil,     &&pstr,   &&newv,
-        &&newh,    &&newf,     &&happ,   &&para,
-        &&defpara, &&dynpara,  &&unot,   &&usub,
-        &&add,     &&sub,      &&mul,    &&div,
-        &&lnk,     &&addc,     &&subc,   &&mulc,
-        &&divc,    &&lnkc,     &&addeq,  &&subeq,
-        &&muleq,   &&diveq,    &&lnkeq,  &&addeqc,
-        &&subeqc,  &&muleqc,   &&diveqc, &&lnkeqc,
-        &&meq,     &&eq,       &&neq,    &&less,
-        &&leq,     &&grt,      &&geq,    &&lessc,
-        &&leqc,    &&grtc,     &&geqc,   &&pop,
-        &&jmp,     &&jt,       &&jf,     &&counter,
-        &&findex,  &&feach,    &&callg,  &&calll,
-        &&upval,   &&callv,    &&callvi, &&callh,
-        &&callfv,  &&callfh,   &&callb,  &&slcbegin,
-        &&slcend,  &&slc,      &&slc2,   &&mcallg,
-        &&mcalll,  &&mupval,   &&mcallv, &&mcallh,
-        &&ret,     &&vmexit
+        &&loadl,   &&loadu,    &&pnum,   &&pnil,
+        &&pstr,    &&newv,     &&newh,   &&newf,
+        &&happ,    &&para,     &&defpara,&&dynpara,
+        &&unot,    &&usub,     &&add,    &&sub,
+        &&mul,     &&div,      &&lnk,    &&addc,
+        &&subc,    &&mulc,     &&divc,   &&lnkc,
+        &&addeq,   &&subeq,    &&muleq,  &&diveq,
+        &&lnkeq,   &&addeqc,   &&subeqc, &&muleqc,
+        &&diveqc,  &&lnkeqc,   &&meq,    &&eq,
+        &&neq,     &&less,     &&leq,    &&grt,
+        &&geq,     &&lessc,    &&leqc,   &&grtc,
+        &&geqc,    &&pop,      &&jmp,    &&jt,
+        &&jf,      &&counter,  &&findex, &&feach,
+        &&callg,   &&calll,    &&upval,  &&callv,
+        &&callvi,  &&callh,    &&callfv, &&callfh,
+        &&callb,   &&slcbegin, &&slcend, &&slc,
+        &&slc2,    &&mcallg,   &&mcalll, &&mupval,
+        &&mcallv,  &&mcallh,   &&ret,    &&vmexit
     };
     bytecode=gen.get_code().data();
     std::vector<const void*> code;
@@ -912,8 +901,6 @@ loadg:   exec_opnodie(opr_loadg   ,op_loadg   ); // -1
 loadl:   exec_opnodie(opr_loadl   ,op_loadl   ); // -1
 loadu:   exec_opnodie(opr_loadu   ,op_loadu   ); // -1
 pnum:    exec_operand(opr_pnum    ,op_pnum    ); // +1
-pone:    exec_operand(opr_pone    ,op_pone    ); // +1
-pzero:   exec_operand(opr_pzero   ,op_pzero   ); // +1
 pnil:    exec_operand(opr_pnil    ,op_pnil    ); // +1
 pstr:    exec_operand(opr_pstr    ,op_pstr    ); // +1
 newv:    exec_operand(opr_newv    ,op_newv    ); // +1-imm[pc]