Recursion replaces mutation-driven iteration with successive calls that pass changing values as arguments. In Clojure, loop and fn forms provide recursion targets, while recur transfers execution to the next iteration. section 3.4
A recursive loop has three essential parts:
- Pass each successive state—such as a counter and result collection—as arguments to the next invocation. section 3.4.4
- Use an exit condition, commonly if or cond, to decide when the computation returns its final value. section 3.4
- Recognize tail recursion when the recursive call is the last instruction in its scope; Clojure uses recur for this loop-style transfer. section 3.4
- Prefer recursion or sequence operations over mutable while loops when expressing iteration in idiomatic functional Clojure. section 3.4.4
Collecting squares
(loop [i 0 s []] (if (< i 10) (recur (inc i) (conj s (* i i))) s)) ;; [0 1 4 9 16 25 36 49 64 81] The counter and collection become loop bindings. Each recur supplies their next values; when the condition fails, s is returned. section 3.4
(loop [i 0 s []]
(if (< i 10)
(recur (inc i) (conj s (* i i)))
s))
;; [0 1 4 9 16 25 36 49 64 81]
View the complete loop-recur example with its executable result. section 3.4
