Returns an iterator which repeatedly calls a function.

The iterator is infinite. Each time it's advanced, it calls (f) and produces the result of the call.

Infinite iterators can be converted to finite iterators using take.

(let n 1)
(let-fn powers ()
  (= n (* n 2))
  n)

(prn ..(take 4 (repeat-with powers))) ; prints 2 4 8 16