I am attempting to Install Drupal 8 on FreeBSD using Apache and Postgresql.

When running drupal/core/install.php Apache responds:

xxx.xxx.xxx.xxx is currently unable to handle this request.

500

httpd-error.log shows:

[:error] [pid xxxxxx] [client xxxxxxx] PHP fatal error: Call to undefined function Symfony//Component//Yaml//ctype_digit() in ****

/usr/local/www/apache24/data/drupal/vendor/symfony/yaml/Inline.php on line 504

that line contains:

case ctype_digit($scalar):

Can anyone tell me what I need to do at this point?

**** the line marked with **** should have backslashes rather than forward slashes - my keyboard has suddenly developed a fault.