diff --git a/main.cpp b/main.cpp
index 4951747..e0c7f9d 100644
--- a/main.cpp
+++ b/main.cpp
@@ -53,6 +53,7 @@ void execute(std::string& file,std::string& command)
 		return;
 	}
 	parse.set_toklist(lexer.get_token_list());
+	lexer.get_token_list().clear();
 	parse.main_process();
 	if(parse.get_error())
 	{
@@ -65,6 +66,7 @@ void execute(std::string& file,std::string& command)
 		return;
 	}
 	import.link(parse.get_root());
+	parse.get_root().clear();
 	if(import.get_error())
 	{
 		die("import",file);
diff --git a/nasal_import.h b/nasal_import.h
index f268832..0009ecf 100644
--- a/nasal_import.h
+++ b/nasal_import.h
@@ -87,18 +87,19 @@ nasal_ast nasal_import::file_import(nasal_ast& node)
     import_lex.scanner();
     if(import_lex.get_error())
     {
-        this->die(filename,"lexer");
+        die(filename,"lexer");
         return tmp;
     }
     import_par.set_toklist(import_lex.get_token_list());
+    import_lex.get_token_list().clear();
     import_par.main_process();
     if(import_par.get_error())
     {
-        this->die(filename,"parser");
+        die(filename,"parser");
         return tmp;
     }
     tmp=import_par.get_root();
-
+    import_par.get_root().clear();
     // check if tmp has 'import'
     return load(tmp);
 }
diff --git a/nasal_lexer.h b/nasal_lexer.h
index 5abefd8..6a90739 100644
--- a/nasal_lexer.h
+++ b/nasal_lexer.h
@@ -125,7 +125,8 @@ void nasal_lexer::openfile(std::string filename)
     {
 		++error;
         std::cout<<">> [lexer] cannot open file \""<<filename<<"\".\n";
-        fin.close();
+		fin.close();
+		res_size=0;
         return;
     }
     while(!fin.eof())
@@ -390,6 +391,7 @@ void nasal_lexer::scanner()
 	}
 	token tk(line,tok_eof,"");
 	token_list.push_back(tk);
+	res.clear();
 	return;
 }