[crabbone]

I used Prolog twice in production, but none of them were what I'd expect to be the "typical" uses.

1. I used GoLog (a Prolog interpreted in Go) for defining some functional tests in the project where the testing infrastructure was otherwise written in Go.

2. I used Prolog (SWI) to write a parser for Thrift (both the definition and binary format) simply because I needed one, and Prolog was convenient.

What I expect people who use Prolog for the stuff it's really good at is databases that encode some complicated business or legal processes. I.e. databases with many complex constraints that have to all somehow come together to produce a solution set. Prolog would also be a good language to encode / query graph databases. So, whatever you can think of being a good match for a graph database would also work well with Prolog.

There are also (even more niche) Prolog derivatives, eg. Ciao or Mercury, that are... well, decent all-purpose languages. You can just use them in the same context where you'd use Python or Haskell respectively. The implementations are pretty solid in terms of performance and correctness... so, if you like the approach, then why not?