Thanks for the stacktrace,
Looks like my bad - a bug in the lisp-side SDL bindings (missing event type). That's interesting... have to dig into SDL source how that can happen.
Do you have maybe some unusual hardware such as joystick/foot pedals? (Trying to see if such an event type could be coming from).
For now this could be the quickest fix (pushed that to gitlab too):
--- a/lisp/racerdemo.lisp +++ b/lisp/racerdemo.lisp @@ -95,7 +95,7 @@ (let ((event (sdl2:make-event))) (unwind-protect (loop while (plusp (sdl2:poll-event event)) do - (let ((event-type (cffi:mem-ref event 'sdl2:event-type))) + (let ((event-type (ignore-errors (cffi:mem-ref event 'sdl2:event-type)))) (handle event-type event))) (cffi:foreign-free event))))