GraphQL\Examples\Blog\Type\Scalar\EmailType::parseLiteral PHP Method

    public static function parseLiteral($valueNode)
    {
        // Note: throwing GraphQL\Error\Error vs \UnexpectedValueException to benefit from GraphQL
        // error location in query:
        if (!$valueNode instanceof StringValueNode) {
            throw new Error('Query error: Can only parse strings got: ' . $valueNode->kind, [$valueNode]);
        }
        if (!filter_var($valueNode->value, FILTER_VALIDATE_EMAIL)) {
            throw new Error("Not a valid email", [$valueNode]);
        }
        return $valueNode->value;
    }