exception OutOfRange of int*int;

     fun comb1(n,m) =
             if n <= 0 then raise OutOfRange(n,m)
             else if m < 0 orelse m > n then
                     raise OutOfRange(n,m)
             else if m=0 orelse m=n then 1
             else comb1(n-1,m) + comb1(n-1,m-1);

     fun comb(n,m) = comb1(n,m) handle
             OutOfRange(0,0) => 1 |
             OutOfRange(n,m) => (
                     print("out of range: n=");
                     print(Int.toString(n));
                     print(" m=");
                     print(Int.toString(m));
                     print("\n");
                     0
                 );

     comb(4,2);

     comb(3,4);

     comb(0,0);