Yeah I don't know how stickers trace code, but FlowStorm tracing debugger takes advantage of the immutable data structures used everywhere and by default in Clojure. You can then instrument entire code bases, run them, and tracing is just a matter of retaining(leaking) pointers of every intermediate expression so the GC doesn't collect them. I don't think this is possible when working with mutable objects, since then only way would be to somehow serialize the objects involved at every step so you can analyze the data later, which is prohibitively expensive in most situations.
Yeah I don't know how stickers trace code, but FlowStorm tracing debugger takes advantage of the immutable data structures used everywhere and by default in Clojure. You can then instrument entire code bases, run them, and tracing is just a matter of retaining(leaking) pointers of every intermediate expression so the GC doesn't collect them. I don't think this is possible when working with mutable objects, since then only way would be to somehow serialize the objects involved at every step so you can analyze the data later, which is prohibitively expensive in most situations.