> I haven’t encountered any other way to write iterative expressions whose number of iterations isn’t known at the top (like map and reduce). `unfold`, Rust's

> I haven’t encountered any other way to write iterative expressions whose number of iterations isn’t known at the top (like map and reduce). `unfold`, Rust's `loop`, generators, working tail recursion elimination (the lack of which loop/recur is a workaround for)