We can improve slightly on the Collatz examples of Chapter 10 of Learning J by noting that, while taking a function power of infinity produces the fixed-point, taking a function power of boxed infinity (or simply the empty box) also gives us back the intermediate values. Let’s start by bringing back the function itself: collatz =. -:`(1 + 3 * ])@.(2&|) To review briefly, we can treat f`g@.t as false`true @. test In other words, this is a very condensed version of what in C would look someth...
