eratosthene

let rec eratosthene n =
    if n < 2 then
        [ ]
    else
        let primes = eratosthene ( n - 1 ) in
        let rec is_prime primes n =
            match primes with
                | [ ] -> true
                | head :: tail -> n mod head <> 0 && is_prime tail n
        in
        if is_prime primes n then
            primes @ [ n ] (* I don't know if I should reverse the list or not... because appending would be faster but 2 divides more numbers than 3 etc. so it would take longer to find out a number isn't a prime... *)
        else
            primes
;;

let rec print_list l =
    match l with
        | [ ] -> ( )
        | head :: tail -> begin
            print_int head;
            print_newline ( );
            print_list tail
        end
;;

print_list ( eratosthene 100 );;