fun compose (f, g) =
    \(x) => f (g (x))

fun id (x) = x

fun twice (x) = 2 * x

val main =
    print_int (twice (21));
    print_int (compose (id, twice) (21));
    print_int (compose (twice, id) (21));
    print_int (compose (twice, twice) (10))