It's nowhere near that suicidal. In this particular case, the game is being run using modifications to Unity, a very well-established game-engine, so C++ is al

It's nowhere near that suicidal. In this particular case, the game is being run using modifications to Unity, a very well-established game-engine, so C++ is already doing the heavy lifting (alongside Unity's way of writing GPU shaders). Clojure is being used in place of the usual C# for game logic scripting and the like. It's much less performance-critical and so using something like Clojure is a lot less nonsensical. Whether they're optimizing for the right things in picking Clojure over some other language is maybe up for debate (I'd guess their way would be easier to iterate changes, but harder to debug, and the clojure-on-unity stack they're using is pretty much alpha quality), but Naughty Dog already showed that commercial games can use a Lisp in a similar part of the stack with some measure of success.