diff --git a/version0.15/version0.15.2/abstract_syntax_tree.h b/version0.15/version0.15.2/abstract_syntax_tree.h
index e2c05a8..78f6d64 100644
--- a/version0.15/version0.15.2/abstract_syntax_tree.h
+++ b/version0.15/version0.15.2/abstract_syntax_tree.h
@@ -43,20 +43,25 @@ class ast_tree_node
 		{
 			return children;
 		}
-		virtual void print_all_tree()
+		virtual void print_all_tree(int tabnum=0)
 		{
+			for(int i=0;i<tabnum;++i)
+				std::cout<<" ";
 			if(type==__number)
 			{
-				std::cout<<"( num )";
+				std::cout<<"[ number ]"<<std::endl;
 				return;
 			}
-			std::cout<<"( ";
+			std::cout<<"{ ";
 			print_token(type);
+			std::cout<<std::endl;
 			for(std::list<ast_tree_node>::iterator i=children.begin();i!=children.end();++i)
 			{
-				i->print_all_tree();
+				i->print_all_tree(tabnum+1);
 			}
-			std::cout<<" )";
+			for(int i=0;i<tabnum;++i)
+				std::cout<<" ";
+			std::cout<<"}"<<std::endl;
 			return;
 		}
 };
diff --git a/version0.15/version0.15.2/code_generator.h b/version0.15/version0.15.2/code_generator.h
index 58a5ba6..f315499 100644
--- a/version0.15/version0.15.2/code_generator.h
+++ b/version0.15/version0.15.2/code_generator.h
@@ -62,6 +62,8 @@ class code_generator
 		}
 		void run()
 		{
+			root.return_list().clear();
+			bool iserror=false;
 			while(!parse.empty())
 			{
 				switch(parse.top().type)
@@ -69,7 +71,7 @@ class code_generator
 					case __number:number_generator();break;
 					case __add_operator:operator_generator();break;
 					case __sub_operator:operator_generator();break;
-					default:std::cout<<">>[Error] line "<<parse.top().line<<" parse error.\n";break;
+					default:std::cout<<">>[Error] line "<<parse.top().line<<" parse error.\n";iserror=true;break;
 				}
 				parse.pop();
 			}
@@ -78,6 +80,8 @@ class code_generator
 				root.return_list().push_back(node_stack.top());
 				node_stack.pop();
 			}
+			if(iserror)
+				return;
 			std::cout<<">>[Parse] 0 error(s)."<<std::endl;
 			std::cout<<">>[Parse] Complete checking."<<std::endl;
 			root.print_all_tree();
diff --git a/version0.15/version0.15.2/nasal_parser.h b/version0.15/version0.15.2/nasal_parser.h
index c7cb5a3..6eabed5 100644
--- a/version0.15/version0.15.2/nasal_parser.h
+++ b/version0.15/version0.15.2/nasal_parser.h
@@ -18,6 +18,8 @@ class nasal_parser
 	public:
 		void print_parser_stack()
 		{
+			if(parser.empty())
+				return;
 			int line=0;
 			std::stack<parse_unit> temp;
 			while(!parser.empty())