(import std.List)

(let gen_string (fun (length) {
  (mut output "")
  (while (< (len output) length) {
    (set output (+ output (@ "[]" (random 0 1)))) })
  output }))

(let balanced? (fun (str) {
  (mut i 0)
  (=
    (len str)
    (len
      (list:takeWhile str (fun (char) {
        (if (= "[" char)
          (set i (+ i 1))
          (set i (- i 1)))
        (>= i 0) }))))}))

(list:forEach
  (list:iota 0 5)
  (fun (_) {
    (let str (gen_string (random 2 8)))
    (print (string:format "{:<8}: {:^6}" str (if (balanced? str) "OK" "NOT OK"))) }))