[bjz_]

As Mike says in a sibling comment, we use it quite heavily for implementing our HTML-to-PDF browser engine, https://www.princexml.com

It's a pretty handy general purpose language, kind of a combination of Prolog and Haskell. It's much easier to maintain a long-lived project in Mercury than one in Prolog due to the static typing, and it also generates much more efficient code. That said, it doesn't have the greatest documentation, so you might have to reach out on IRC, or the mailing list if you run into some challenges with it.