quick implementation of the Tower Of Hanoi problem

hanoi-tower.re

type rod = list(int);

exception InvalidMove(int, int);

exception OtherMove(rod, rod);

let moveRods = (a: rod, b: rod) : (rod, rod) =>
  switch (a, b) {
  | ([x, ...xs], []) => (xs, [x])
  | ([x, ...xs], [y, ...ys]) when x < y => (xs, [x, y, ...ys])
  | ([x, ...xs], [y, ...ys]) => raise(InvalidMove(x, y))
  | (xs, ys) => raise(OtherMove(xs, ys))
  };

let rec move = (n: int, src: rod, dst: rod, aux: rod) : (rod, rod, rod) =>
  if (n > 0) {
    let (src, aux, dst) = move(n - 1, src, aux, dst);
    let (src, dst) = moveRods(src, dst);
    let (aux, dst, src) = move(n - 1, aux, dst, src);
    (src, dst, aux);
  } else {
    (src, dst, aux);
  };

let hanoi = (src: rod) => move(src |> List.length, src, [], []);

let _init = Array.init(23, x => x) |> Array.to_list;

let (a, b, c) = hanoi(_init);

Js.log(b); /*would be exactly same as `a`*/