title: Lex - Warning, rule cannot be matched
body: <p>I'm trying to make .l file but warning occur in certain lines that rule can't be matched</p>
  
  <pre><code>"true"                      return TRUE;
  "false"                     return FALSE;
  "int"                       return INT;
  "char"                      return CHAR;
  "float"                     return FLOAT;
  "bool"                      return BOOLEAN;
  
  "if"                    return IF;
  "else"                  return ELSE;
  "for"                   return FOR;
  "while"                 return WHILE;
  "do"                    return DO;
  "switch"                return SWITCH;
  "case"                  return CASE;
  
  "break"                 return BREAK;
  "default"               return DEFAULT;
  </code></pre>