diff --git a/version2.0/nasal_enum.h b/version2.0/nasal_enum.h
index d9331a3..9e9176e 100644
--- a/version2.0/nasal_enum.h
+++ b/version2.0/nasal_enum.h
@@ -68,30 +68,29 @@ void print_parse_token(int type)
 	std::string context="";
 	switch(type)
 	{
-		case __stack_end:         context="#";  break;
+		case __stack_end:         context=" # ";  break;
+		case __cmp_equal:         context=" == "; break;
+		case __cmp_not_equal:     context=" != "; break;
+		case __cmp_less:          context=" < ";  break;
+		case __cmp_less_or_equal: context=" <= "; break;
+		case __cmp_more:          context=" > ";  break;
+		case __cmp_more_or_equal: context=" >= "; break;
 		
-		case __cmp_equal:         context="=="; break;
-		case __cmp_not_equal:     context="!="; break;
-		case __cmp_less:          context="<";  break;
-		case __cmp_less_or_equal: context="<="; break;
-		case __cmp_more:          context=">";  break;
-		case __cmp_more_or_equal: context=">="; break;
+		case __and_operator:      context=" and ";break;
+		case __or_operator:       context=" or "; break;
+		case __nor_operator:      context=" ! ";  break;
+		case __add_operator:      context=" + ";  break;
+		case __sub_operator:      context=" - ";  break;
+		case __mul_operator:      context=" * ";  break;
+		case __div_operator:      context=" / ";  break;
+		case __link_operator:     context=" ~ ";  break;
 		
-		case __and_operator:      context="and";break;
-		case __or_operator:       context="or"; break;
-		case __nor_operator:      context="!";  break;
-		case __add_operator:      context="+";  break;
-		case __sub_operator:      context="-";  break;
-		case __mul_operator:      context="*";  break;
-		case __div_operator:      context="/";  break;
-		case __link_operator:     context="~";  break;
-		
-		case __equal:             context="=";  break;
-		case __add_equal:         context="+="; break;
-		case __sub_equal:         context="-="; break;
-		case __mul_equal:         context="*="; break;
-		case __div_equal:         context="/="; break;
-		case __link_equal:        context="~="; break;
+		case __equal:             context=" = ";  break;
+		case __add_equal:         context=" += "; break;
+		case __sub_equal:         context=" -= "; break;
+		case __mul_equal:         context=" *= "; break;
+		case __div_equal:         context=" /= "; break;
+		case __link_equal:        context=" ~= "; break;
 		
 		case __left_brace:        context="{";  break;
 		case __right_brace:       context="}";  break;
@@ -108,18 +107,18 @@ void print_parse_token(int type)
 		
 		case __unknown_operator:  context="unknown_operator";break;
 		
-		case __var:               context="var";      break;
-		case __func:              context="func";     break;
-		case __continue:          context="continye"; break;
+		case __var:               context="var ";      break;
+		case __func:              context="func ";     break;
+		case __continue:          context="continue"; break;
 		case __break:             context="break";    break;
 		case __for:               context="for";      break;
 		case __forindex:          context="forindex"; break;
-		case __foreach:           context="foreach";  break;
+		case __foreach:           context="foreach ";  break;
 		case __while:             context="while";    break;
-		case __if:                context="if";       break;
-		case __elsif:             context="elsif";    break;
-		case __else:              context="else";     break;
-		case __return:            context="return";   break;
+		case __if:                context="if ";       break;
+		case __elsif:             context="elsif ";    break;
+		case __else:              context="else ";     break;
+		case __return:            context="return ";   break;
 		case __nil:               context="nil";      break;
 		
 		case __id:                context="identifier";   break;
diff --git a/version2.0/nasal_parse.h b/version2.0/nasal_parse.h
index 0c4d7d9..a00bb4c 100644
--- a/version2.0/nasal_parse.h
+++ b/version2.0/nasal_parse.h
@@ -9,12 +9,12 @@ class nasal_parse
 		std::stack<token> checked_tokens;
 		token this_token;
 		int error;
-		int warning;
 		abstract_syntax_tree root;
 	public:
 		// basic
 		void delete_all_elements()
 		{
+			// used in 'del' command
 			while(!parse_token_stream.empty())
 				parse_token_stream.pop();
 			while(!checked_tokens.empty())
@@ -30,14 +30,14 @@ class nasal_parse
 		abstract_syntax_tree& get_root();
 
 		// check '(' confliction
-		bool check_multi_assignment();// multi_call_id = multi_scalar
-		bool check_multi_scalar();
-		bool check_var_in_curve();    // multi_definition
+		bool check_multi_assignment();// check multi_call_id '=' multi_scalar
+		bool check_multi_scalar();    // check multi_scalar
+		bool check_var_in_curve();    // check multi_definition: (var id,id,id)
 
 		// abstract_syntax_tree generation
+		// block statements generation
 		void main_generate();
-		abstract_syntax_tree statements_block_generate();
-		abstract_syntax_tree multi_scalar_assignment();
+		abstract_syntax_tree block_generate();
 /*
 		calculation() will get elements generated by and_calculation()
 		and_calculation() will get elements generated by or_calculation()
@@ -64,7 +64,9 @@ class nasal_parse
 		abstract_syntax_tree vector_generate();
 		abstract_syntax_tree function_generate();
 
+		// return_expr() generates ebnf: <return> [<calculation>] ';'
 		abstract_syntax_tree return_expr();
+		abstract_syntax_tree multi_scalar_assignment();
 		abstract_syntax_tree definition();
 		abstract_syntax_tree loop_expr();
 		abstract_syntax_tree choose_expr();
@@ -72,26 +74,30 @@ class nasal_parse
 
 void nasal_parse::print_detail_token()
 {
+	// copy tokens from parse_token_stream
+	// so this function only works when generation hasn't begun.
 	std::stack<token> tmp=parse_token_stream;
-	std::string space="";
+	// indent
+	std::string indent="";
 	int line=1;
 	std::cout<<line<<"\t";
-	while(tmp.top().type!=__stack_end)
+	while((!tmp.empty()) && (tmp.top().type!=__stack_end))
 	{
 		if(tmp.top().line!=line)
 		{
+			// if line changes,print '\n' and number of line
 			for(int i=line+1;i<tmp.top().line;++i)
 				std::cout<<std::endl<<i<<"\t";
 			line=tmp.top().line;
-			std::cout<<std::endl<<line<<"\t"<<space;
+			std::cout<<std::endl<<line<<"\t"<<indent;
 		}
 		print_parse_token(tmp.top().type);
+
 		if(tmp.top().type==__left_brace)
-			space+=' ';
-		std::cout<<" ";
+			indent+=' ';
 		tmp.pop();
-		if(!tmp.empty() && tmp.top().type==__right_brace)
-			space.pop_back();
+		if((!tmp.empty()) && (tmp.top().type==__right_brace))
+			indent.pop_back();
 	}
 	std::cout<<std::endl;
 	return;
@@ -103,13 +109,15 @@ void nasal_parse::get_token_list(std::list<token>& detail_token_stream)
 		parse_token_stream.pop();
 	while(!checked_tokens.empty())
 		checked_tokens.pop();
+	// add stack_end token
 	token end_token;
 	end_token.line=0;
 	end_token.str="stack_end";
 	end_token.type=__stack_end;
+
 	parse_token_stream.push(end_token);
 	checked_tokens.push(end_token);
-	// clear stacks and initialize them with end_token
+	// clear stacks and initialize them with stack_end token
 
 	std::stack<token> backward_tmp;
 	// backward_tmp is used to backward detail_token_stream
@@ -134,7 +142,10 @@ void nasal_parse::get_token()
 		checked_tokens.push(this_token);
 	}
 	if(this_token.type==__stack_end)
+	{
+		std::cout<<">>[Parse-error] fatal error."<<std::endl;
 		std::cout<<">>[Stack-end] empty token stack."<<std::endl;
+	}
 	return;
 }
 
@@ -147,7 +158,10 @@ void nasal_parse::push_token()
 		checked_tokens.pop();
 	}
 	if(this_token.type==__stack_end)
+	{
+		std::cout<<">>[Parse-error] fatal error."<<std::endl;
 		std::cout<<">>[Stack-end] empty token stack."<<std::endl;
+	}
 	return;
 }
 
@@ -183,6 +197,12 @@ bool nasal_parse::check_multi_assignment()
 		{
 			this->get_token();
 			++cnt;
+			// these determine statements are used with curve_cnt,bracket_cnt and brace_cnt together
+			// to avoid checking commas in other curves/brackets/braces
+			// such as ([0,1,2,3])
+			// but in multi_assignment, only things like (id[scalar],id.id[scalar]) can be recognized as multi_scalar
+			// if ([0,1,2,3]) and i don't use these judgements,then ([0,1,2,3]) will be recognized as multi_scalar
+			// but in fact ([0,1,2,3]) is not
 			if(this_token.type==__left_curve)   ++curve_cnt;
 			if(this_token.type==__left_bracket) ++bracket_cnt;
 			if(this_token.type==__left_brace)   ++brace_cnt;
@@ -220,6 +240,9 @@ bool nasal_parse::check_multi_scalar()
 	{
 		this->get_token();
 		++cnt;
+		// these determine statements are used with curve_cnt,bracket_cnt and brace_cnt together
+		// to avoid checking commas in other curves/brackets/braces
+		// such as (a[0,1,2],b(2,3))
 		if(this_token.type==__left_curve)   ++curve_cnt;
 		if(this_token.type==__left_bracket) ++bracket_cnt;
 		if(this_token.type==__left_brace)   ++brace_cnt;
@@ -245,11 +268,11 @@ bool nasal_parse::check_multi_scalar()
 bool nasal_parse::check_var_in_curve()
 {
 	bool ret=false;
-	this->get_token();// get '('
-	this->get_token();
-	ret=(this_token.type==__var);
-	this->push_token();
-	this->push_token();
+	this->get_token();           // get '('
+	this->get_token();           // get 'var' if exists
+	ret=(this_token.type==__var);// check
+	this->push_token();          // push 'var'
+	this->push_token();          // push '('
 	return ret;
 }
 
@@ -258,8 +281,7 @@ void nasal_parse::main_generate()
 	statement_generate_state=stat_null;
 	// initialize state
 	error=0;
-	warning=0;
-	// initialize error and warning
+	// initialize error
 	root.set_clear();
 	root.set_node_line(1);
 	root.set_node_type(__root);
@@ -310,11 +332,11 @@ void nasal_parse::main_generate()
 		}
 
 	}
-	std::cout<<">>[Parse] complete generation. "<<error<<" error(s), "<<warning<<" warning(s)."<<std::endl;
+	std::cout<<">>[Parse] complete generation. "<<error<<" error(s)."<<std::endl;
 	return;
 }
 
-abstract_syntax_tree nasal_parse::statements_block_generate()
+abstract_syntax_tree nasal_parse::block_generate()
 {
 	abstract_syntax_tree block_node;
 	abstract_syntax_tree continue_break_node;
@@ -454,7 +476,7 @@ abstract_syntax_tree nasal_parse::multi_scalar_assignment()
 	{
 		front_multi_scalar_node.add_children(scalar_generate());
 		this->get_token();
-		if(this_token.type!=__comma && this_token.type!=__right_curve)
+		if((this_token.type!=__comma) && (this_token.type!=__right_curve))
 		{
 			++error;
 			print_parse_error(multi_assignment_need_curve,this_token.line,this_token.type);
@@ -470,6 +492,7 @@ abstract_syntax_tree nasal_parse::multi_scalar_assignment()
 	this->get_token();
 	assignment_node.set_node_line(this_token.line);
 	assignment_node.set_node_type(this_token.type);
+	// only '=' is alowed in multi_assignment
 	if(this_token.type!=__equal)
 	{
 		++error;
@@ -490,7 +513,7 @@ abstract_syntax_tree nasal_parse::multi_scalar_assignment()
 			{
 				back_multi_scalar_node.add_children(scalar_generate());
 				this->get_token();
-				if(this_token.type!=__comma && this_token.type!=__right_curve)
+				if((this_token.type!=__comma) && (this_token.type!=__right_curve))
 				{
 					++error;
 					print_parse_error(multi_assignment_need_curve,this_token.line,this_token.type);
@@ -884,7 +907,7 @@ abstract_syntax_tree nasal_parse::scalar_generate()
 				{
 					call_vector_node.add_children(calculation());
 					this->get_token();
-					if(this_token.type!=__comma && this_token.type!=__right_bracket)
+					if((this_token.type!=__comma) && (this_token.type!=__right_bracket))
 					{
 						++error;
 						print_parse_error(call_vector_lack_bracket,this_token.line,this_token.type);
@@ -1053,7 +1076,7 @@ abstract_syntax_tree nasal_parse::function_generate()
 			else
 			{
 				++error;
-				print_parse_error(parameter_lack_part,this_token.line);
+				print_parse_error(parameter_lack_part,this_token.line,this_token.type);
 				break;
 			}
 
@@ -1076,7 +1099,7 @@ abstract_syntax_tree nasal_parse::function_generate()
 			if((this_token.type!=__right_curve) && (this_token.type!=__comma))
 			{
 				++error;
-				print_parse_error(parameter_lack_curve,this_token.line);
+				print_parse_error(parameter_lack_curve,this_token.line,this_token.type);
 				break;
 			}
 			if(this_token.type==__comma)
@@ -1090,7 +1113,7 @@ abstract_syntax_tree nasal_parse::function_generate()
 	}
 	else
 		this->push_token();
-	function_node.add_children(statements_block_generate());
+	function_node.add_children(block_generate());
 	return function_node;
 }
 
@@ -1224,7 +1247,7 @@ abstract_syntax_tree nasal_parse::definition()
 				{
 					this->push_token();
 					++error;
-					print_parse_error(definition_wrong_type,this_token.line);
+					print_parse_error(definition_wrong_type,this_token.line,this_token.type);
 					break;
 				}
 				else
@@ -1419,7 +1442,7 @@ abstract_syntax_tree nasal_parse::loop_expr()
 			print_parse_error(lack_right_curve,this_token.line,this_token.type);
 		}
 	}
-	loop_main_node.add_children(statements_block_generate());
+	loop_main_node.add_children(block_generate());
 	return loop_main_node;
 }
 
@@ -1448,7 +1471,7 @@ abstract_syntax_tree nasal_parse::choose_expr()
 		++error;
 		print_parse_error(lack_right_curve,this_token.line);
 	}
-	if_node.add_children(statements_block_generate());
+	if_node.add_children(block_generate());
 	// add statements
 	this->get_token();
 	if(this_token.type==__elsif)
@@ -1472,7 +1495,7 @@ abstract_syntax_tree nasal_parse::choose_expr()
 				++error;
 				print_parse_error(lack_right_curve,this_token.line,this_token.type);
 			}
-			elsif_node.add_children(statements_block_generate());
+			elsif_node.add_children(block_generate());
 			choose_main_node.add_children(elsif_node);
 			this->get_token();// get next 'elsif' if it exists
 		}
@@ -1485,7 +1508,7 @@ abstract_syntax_tree nasal_parse::choose_expr()
 	{
 		else_node.set_node_line(this_token.type);
 		else_node.set_node_type(__else);
-		else_node.add_children(statements_block_generate());
+		else_node.add_children(block_generate());
 		choose_main_node.add_children(else_node);
 	}
 	else
diff --git a/version2.0/parse.ebnf b/version2.0/parse.ebnf
index 7edb2c6..aed3c7e 100644
--- a/version2.0/parse.ebnf
+++ b/version2.0/parse.ebnf
@@ -104,7 +104,7 @@
 
 <continue_expr> = <continue> ;
 <break_expr> = <break> ;
-<return_expr> = <return> [<scalar>] ;
+<return_expr> = <return> [<calculation>] ;
 <statement> =
     <definition>
 |   <assignment>