merge.re

let rec merge x y =>
  switch (x, y) {
  | ([], l) => l
  | (l, []) => l
  | ([hx, ...tx], [hy, ...ty]) =>
    if (hx < hy) {
      [hx, ...merge tx [hy, ...ty]]
    } else {
      [hy, ...merge [hx, ...tx] ty]
    }
  };