Fennel has a form `assert-repl` which will drop into the REPL wherever, if the condition fails. For writing games you can launch the REPL in the game loop if a

Fennel has a form `assert-repl` which will drop into the REPL wherever, if the condition fails. For writing games you can launch the REPL in the game loop if a keyboard button is pressed. But what you can't do, that I know of, is interrupt arbitrary execution and get a Fennel REPL. You'd probably need a lua debugger of some sort for that. I'm not that familiar with that though.