function expectKeyword($value)
{
$token = $this->lexer->token;
if ($token->kind === Token::NAME && $token->value === $value) {
$this->lexer->advance();
return $token;
}
throw new SyntaxError($this->lexer->source, $token->start, 'Expected "' . $value . '", found ' . $token->getDescription());
}