I suspect (but cannot prove) that environment lookups are cached, so that when the new definition is loaded with the same name as the previous jump target, the

I suspect (but cannot prove) that environment lookups are cached, so that when the new definition is loaded with the same name as the previous jump target, the compiled code is invalidated and switches back to interpreted mode. But now that I talk through it, that sounds pretty hard. Occasionally I dive into racket’s good old C code for masochistic pleasure (it’s good code, just … very C, and very old). I always come away with a feeling of “well, that’s an interesting puzzle… I wonder what will happen when X happens” for every X that catches my attention. (Yesterday X was “How do racket’s thread-local parameters propagate their current values to new threads spawned by a subthread?) Still, I’m ~50% confident that my original explanation is right, even if the details are wrong. I would be shocked if a compiled tail-recursive function didn’t jump into its own new definition when a new definition is loaded for the previous jump target (the global function name). Test it out and check what happens empirically. :) Who knows. I’ve switched to Python long ago for daily tasks, since occasionally I enjoy “actually getting things done quickly, rather than endlessly researching interesting theoretical programming questions,” and Python is 60x slower than JavaScript (which doesn’t have tail recursion either), so #shruggyface. The world has apparently decided that tail recursion was an idea best left to the 90’s. EDIT: After thinking it over, I bet you’re right and my original point about tail recursion is mistaken. And indeed, I remember now that in Arc, all the threads tend to be while-loops that just call another global function to do its work. Probably for this exact reason. Very impressive callout. And a nice reminder to limit myself to talking about the things I actually do, not what I might theoretically do. At least not without qualifications and disclaimers. Thanks!