If you look at it with enough vagueness, I've seen some form of this at every job I've had: someone has a problem to solve, and has an idea that is fun to imple

If you look at it with enough vagueness, I've seen some form of this at every job I've had: someone has a problem to solve, and has an idea that is fun to implement, unnecessarily flexible, and possibly Turing-complete. It's a way of getting the "I did a cool hack" dopamine hits that we nerds love so much, while still doing our jobs. Depending on how well they did at keeping their actual goal in mind, you might wind up with a very useful embedded scripting engine, or a very bad ad hoc build system for a project that did not need its own build system. (I've seen both.) I would expect there's a large overlap between people who think Lisp and/or Prolog are cool, and people who are prone to doing this sort of thing. Non-trivial knowledge of either of those correlates strongly with being more into programming than the average developer.