Shuffle Deck

// Fisher–Yates shuffle
let shuffle deck =
    let n = Array.length deck
    let rnd = new Random()
    let pick n = rnd.Next n
    let swap i j = 
        let a,b = deck.[i], deck.[j]
        Array.set deck j a
        Array.set deck i b

    for i = n - 1 downto 0 do
        swap i (pick i)
    deck

type Suit = Clubs | Diamonds | Hearts | Spades
type Value = 
    | Ace    = 1
    | ``2``  = 2
    | ``3``  = 3
    | ``4``  = 4
    | ``5``  = 5
    | ``6``  = 6
    | ``7``  = 7
    | ``8``  = 8
    | ``9``  = 9
    | ``10`` = 10
    | Jack   = 11
    | Queen  = 12
    | King   = 13

type Cards = Card of suit: Suit * value: Value
let values = [1..13] |> List.map enum<Value>
let suits = [Clubs; Diamonds; Hearts; Spades]
let deck = List.allPairs suits values |> List.map Card

shuffle (deck |> List.toArray)