There is a setting in the admin panel which controls the highlighters that are included on the page for highlighting preformatted code blocks.
To request a new highlighter be added, make a comment on this topic with the requested language.
It looks like this forum software uses the highlightJS library, and PureScript currently doesn’t have a formatter there. Here’s an issue I made to request someone to add it: https://github.com/isagalaev/highlight.js/issues/1739