code: public function moveNext()
      {
          $this->peek = 0;
          $this->token = $this->lookahead;
          $this->lookahead = (isset($this->tokens[$this->position]))
              ? $this->tokens[$this->position++] : null;
  
          return $this->lookahead !== null;
      }
docs: Moves to the next token in the input string.
  
  @return boolean