shuffle.sml

local
    fun rmod x y = x - y * Real.realFloor (x / y);
    val a = 16807.0;
    val m = 2147483647.0;
    val random_seed = ref 1.0;
in
    fun random () =
    let
        val r = rmod (a * ! random_seed) m
    in
        random_seed := r;
        Real.floor r
    end
end;

fun removeElement ([], _) = []
  | removeElement (first::rest, x) =
    if first = x then
        rest
    else
        first::removeElement (rest, x)

fun shuffle [] = []
  | shuffle l =
    let
        val index = random () mod (length l)
        val element = List.nth (l, index)
        val l = removeElement (l, element)
    in
        element::shuffle l
    end