code: protected void checkFor(VDMToken tok, int number, String message)
  			throws LexException, ParserException
  	{
  		if (lastToken().is(tok))
  		{
  			nextToken();
  		} else
  		{
  			throwMessage(number, message);
  		}
  	}
docs: If the last token is as expected, advance, else raise an error.
  
  @param tok
  The token type to check for.
  @param number
  The error number.
  @param message
  The error message to raise if the token is not as expected.
  @throws LexException
  @throws ParserException