Added FizzBuzz

fizzbuzz.sml

(*
 * A original problem is here.
 * https://twitter.com/kokuyouwind/status/1141602930019061760
 *)

fun fizzBuzz n =
  let
    val div3 = n mod 3 = 0
    val div5 = n mod 5 = 0
  in
    case (div3, div5) of
        (true, true) => "fizzbuzz"
      | (true, false) => "fizz"
      | (false, true) => "buzz"
      | (false, false) =>
        Int.toString n
  end

(*
 * If a arg2 of function is true, the divisible is reversed.
 *
 *  arg2  | divN  | case
 * ---------------------
 *  true  | true  | false
 *  true  | false | true
 *  false | true  | true
 *  false | false | false
 *
 *  equals xor!!
 *)
fun xor (b1, b2) = not (b1 = b2)
fun fizzBuzzPlus1 n b =
  let
    val div3 = n mod 3 = 0
    val div5 = n mod 5 = 0
  in
    case (xor (div3, b), xor (div5, b)) of
        (true, true) => "fizzbuzz"
      | (true, false) => "fizz"
      | (false, true) => "buzz"
      | (false, false) =>
        Int.toString n
  end

fun fizzBuzzPlus2 n b =
  let
    fun xor3 (b1, b2, b3) = xor (xor (b1, b2), b3)
    val div3 = n mod 3 = 0
    val div5 = n mod 5 = 0
    val neg = n < 0
  in
    case (xor3 (div3, b, neg), xor3 (div5, b, neg)) of
        (true, true) => "fizzbuzz"
      | (true, false) => "fizz"
      | (false, true) => "buzz"
      | (false, false) =>
        Int.toString n
  end