(*  primes2.ml 
    Prime number generator, take 2
    Tyler Eaves <tyler@ml1.net>
    *)
   
exception Not_prime;;
exception Its_Prime;;

let rec isprime n primes = (
    try
        List.iter (fun x -> if n mod x = 0 then raise Not_prime else if sqrt
        (float_of_int n) < (float_of_int x) then raise Its_Prime else ()) primes;
        Printf.printf "%d is PRIME!\n" n; 
        isprime (n+2) (List.concat [primes; [n]])
    with 
        Not_prime -> isprime (n+2) primes
        | Its_Prime -> (Printf.printf "%d is PRIME!\n" n; 
          isprime (n+2) (List.concat [primes; [n]]))
    );;

isprime 3 [2];;