diff --git a/makefile b/makefile
index ab5025e..c514751 100644
--- a/makefile
+++ b/makefile
@@ -1,7 +1,9 @@
 .PHONY=test
-nasal:main.cpp nasal_ast.h nasal_err.h nasal_builtin.h nasal_opt.h nasal_codegen.h nasal_gc.h nasal_import.h nasal_lexer.h nasal_parse.h nasal_vm.h nasal_dbg.h nasal.h
+nasal:main.cpp nasal_ast.h nasal_err.h nasal_builtin.h nasal_opt.h nasal_codegen.h\
+      nasal_gc.h nasal_import.h nasal_lexer.h nasal_parse.h nasal_vm.h nasal_dbg.h nasal.h
 	clang++ -std=c++11 -O3 main.cpp -o nasal -fno-exceptions -ldl -Wshadow -Wall
-nasal.exe:main.cpp nasal_ast.h nasal_err.h nasal_builtin.h nasal_opt.h nasal_codegen.h nasal_gc.h nasal_import.h nasal_lexer.h nasal_parse.h nasal_vm.h nasal_dbg.h nasal.h
+nasal.exe:main.cpp nasal_ast.h nasal_err.h nasal_builtin.h nasal_opt.h nasal_codegen.h\
+      nasal_gc.h nasal_import.h nasal_lexer.h nasal_parse.h nasal_vm.h nasal_dbg.h nasal.h
 	g++ -std=c++11 -O3 main.cpp -o nasal.exe -fno-exceptions -Wshadow -Wall -static
 test:nasal
 	@ ./nasal -op -e test/ascii-art.nas
diff --git a/nasal_codegen.h b/nasal_codegen.h
index ee6f52b..c00571c 100644
--- a/nasal_codegen.h
+++ b/nasal_codegen.h
@@ -201,7 +201,7 @@ private:
     // local  : max 32768 upvalues 65536 values
     std::list<std::unordered_map<std::string,int>> local;
 
-    // func end stack, reserved for print
+    // func end stack, reserved for code print
     std::stack<uint32_t> fbstk;
     std::stack<uint32_t> festk;
     
@@ -896,14 +896,14 @@ void nasal_codegen::forindex_gen(const nasal_ast& ast)
     gen(op_cnt,0,ast[1].line());
     int ptr=code.size();
     gen(op_findex,0,ast.line());
-    if(ast[0].type()==ast_iter)
+    if(ast[0].type()==ast_iter) // define a new iterator
     {
         const std::string& str=ast[0][0].str();
         local.empty()?
             gen(op_loadg,global_find(str),ast[0][0].line()):
             gen(op_loadl,local_find(str),ast[0][0].line());
     }
-    else
+    else // use exist variable as the iterator
     {
         mcall(ast[0]);
         if(code.back().op==op_mcallg)
@@ -930,14 +930,14 @@ void nasal_codegen::foreach_gen(const nasal_ast& ast)
     gen(op_cnt,0,ast.line());
     int ptr=code.size();
     gen(op_feach,0,ast.line());
-    if(ast[0].type()==ast_iter)
+    if(ast[0].type()==ast_iter) // define a new iterator
     {
         const std::string& str=ast[0][0].str();
         local.empty()?
             gen(op_loadg,global_find(str),ast[0][0].line()):
             gen(op_loadl,local_find(str),ast[0][0].line());
     }
-    else
+    else // use exist variable as the iterator
     {
         mcall(ast[0]);
         if(code.back().op==op_mcallg)
diff --git a/nasal_vm.h b/nasal_vm.h
index affc46c..b82dc80 100644
--- a/nasal_vm.h
+++ b/nasal_vm.h
@@ -196,13 +196,13 @@ void nasal_vm::bytecodeinfo(const char* header,const uint32_t p)
             printf("0x%x",c.num);break;
         case op_callb:
             printf("0x%x <%s@0x%lx>",c.num,builtin[c.num].name,(uint64_t)builtin[c.num].func);break;
+        case op_upval: case op_mupval: case op_loadu:
+            printf(" (0x%x[0x%x])",(c.num>>16)&0xffff,c.num&0xffff);break;
         case op_happ:  case op_pstr:
         case op_lnkc:
         case op_callh: case op_mcallh:
         case op_para:  case op_defpara:case op_dynpara:
             printf("0x%x (\"%s\")",c.num,rawstr(str_table[c.num]).c_str());break;
-        case op_upval: case op_mupval: case op_loadu:
-            printf(" (0x%x[0x%x])",(c.num>>16)&0xffff,c.num&0xffff);break;
         default:printf("0x%x",c.num);break;
     }
     printf(" (%s:%d)\n",files[c.fidx].c_str(),c.line);