To throw in one more data point: several years ago I wrote a simulator for a paper, it involves tracking large numbers of particles bouncing through a 2D space

To throw in one more data point: several years ago I wrote a simulator for a paper, it involves tracking large numbers of particles bouncing through a 2D space with different geometries. There's a front end, in PLT Scheme, and a backend in C. I'm pretty sure that today - the C code would still compile and run - the Scheme code would not without some effort, because PLT Scheme 372 is no longer supported, Racket made a number of breaking changes, so one would either have to rewrite the Scheme code for Racket or rewrite it for another Scheme implementation.