Earlier quoted context omitted.
> while your "average" Lisp might be unsuitable for hard real-time applications (due to the presence of a garbage collector, usually without the hard real-time constraints that you can get out of garbage collectors with extreme effort), I wonder if they have some equivalently interactive system on-board the while your "average" Lisp might be unsuitable for hard real-time applications (due to the presence of a garbage…
As long as there aren't cycles of course you can do deterministic GC, it's just reference counting. It also helps if the program is single-threaded since otherwise any memory allocation/freeing can be unpredictable (since it probably locks.)
Lisp with ref counting (assuming acyclic references) instead of GC could also be interesting to try to hack together. I have a feeling closures would be a particularly quick way to get reference cycles, so some concept of weak references may be necessary.