No, it's not necessary to perform a CPS transformation. After all, the OS manages to pre-emptively schedule any non-cooperating processes, right? So, leaving a

No, it's not necessary to perform a CPS transformation. After all, the OS manages to pre-emptively schedule any non-cooperating processes, right? So, leaving aside the problem of interacting with the OS for I/O, you can do interleaved CPU-bound in a single thread, by instrumenting your code with basically an instruction counter. When it grows a bit too large, stop, reset it, and switch to another task. Erlang does this, although being a functional language, it counts only function calls (no other way to make a loop than to (tail-)call itself). No CPS needed.