ep_9_loop.ml

let triple = (target) =>
  for (a in 1 to target / 3) {
    for (b in a + 1 to target / 2) {
      let c = target - a - b;
      if (a * a + b * b === c * c) {
        Js.log(a * b * c)
      }
    }
  };

triple(1000);

ep_9_recursive.ml

let triple = (target) => {
  let rec next = (a, b) => {
    let c = target - a - b;
    if (a * a + b * b === c * c) {
      a * b * c
    } else if (b < target / 2) {
      next(a, b + 1)
    } else if (a < target / 3) {
      next(a + 1, a + 2)
    } else {
      failwith("Nope.");
    }
  };
  next(1, 2);
};

triple(1000);