let print_pair c =
    let (a, b) = c in
    print_int a;
    print_string "-";
    print_int b
in
let print_tab f tab =
    for i = 0 to (Array.length tab) - 1 do
        f tab.(i);
        print_string "  "
    done
in
let merge_sorting f lt rt =
    let ll = Array.length lt in
    let lr = Array.length rt in
    let l = ll + lr in
    let ret = Array.make (l) 0 in
    let li = ref 0 in
    let ri = ref 0 in
    while (!li < ll && !ri < lr) do
        if ((f lt.(!li) rt.(!ri)) < 0) then
        (
            ret.(!li + !ri) <- rt.(!ri);
            ri := !ri + 1
        )
        else
        (
            ret.(!li + !ri) <- lt.(!li);
            li := !li + 1
        )
    done;
    while (!li < ll) do
        ret.(!li + !ri) <- lt.(!li);
        li := !li + 1
    done;
    while (!ri < lr) do
        ret.(!ri + !li) <- rt.(!ri);
        ri := !ri + 1
    done;
    ret
in
let rec merge_sort f tab =
    let l = Array.length tab in
    if (l < 2) then tab else
    (
        let hl = Array.sub tab 0 (l / 2) in
        let hr = Array.sub tab (l/2) (l - l/2) in
        let sl = merge_sort f hl in
        let sr = merge_sort f hr in
        merge_sorting f sl sr
    )
in
let int_cmp a b = b - a in
let pair_cmp a b =
    let (ax, ay) = a in
    let (bx, by) = b in
    let c = int_cmp ax bx in
    if (c <> 0) then c
    else (int_cmp ay by)
in
let t = (merge_sort pair_cmp [|(2, 7);(3,5);(6,2);(4,1);(1, 0);(79, 3);(4, -2)|]) in
print_tab print_pair t;;