Comparing two Poker hands.

gistfile1.txt

    /// Compare two hands, the first of which can Win, Draw or Lose against the second.
    let CompareHands (hand1 : Hand) (hand2 : Hand) =
        match hand1, hand2 with

        | RoyalFlush, RoyalFlush ->
            raise (ArgumentException("Impossible combination: two Royal Flushes"))
        | RoyalFlush, _ -> Win
        | _, RoyalFlush -> Lose

        | StraightFlush, StraightFlush ->
            let rank1, rank2 = hand1.Cards.[0].Rank, hand2.Cards.[0].Rank
            Outcome.FromRanks rank1 rank2
        | StraightFlush, _ -> Win
        | _, StraightFlush -> Lose

        | FourOfAKind, FourOfAKind 
        | FullHouse, FullHouse ->
            let rank1, rank2 = (hand1.Cards, hand2.Cards) |> Tuple.Map2 CommonestRank
            Outcome.FromRanks rank1 rank2
        | FourOfAKind, _ -> Win
        | _, FourOfAKind -> Lose
        | FullHouse, _ -> Win     
        | _, FullHouse -> Lose           

        | Flush, Flush ->
            // Although normally we would determine on highest rank card, tie breakers
            // may be needed right down to the lowest card so it's easiest to think 
            // of the flush as consisting entirely of kickers.
            let kickers1, kickers2 = (hand1.Cards, hand2.Cards) |> Tuple.Map2 SoloRanks
            CompareKickers kickers1 kickers2
        | Flush, _ -> Win
        | _, Flush -> Lose

        | Straight, Straight ->
            let rank1, rank2 = hand1.Cards.[0].Rank, hand2.Cards.[0].Rank
            Outcome.FromRanks rank1 rank2
        | Straight, _ -> Win
        | _, Straight -> Lose

        | ThreeOfAKind, ThreeOfAKind ->
            let rank1, rank2 = (hand1.Cards, hand2.Cards) |> Tuple.Map2 CommonestRank
            Outcome.FromRanks rank1 rank2
        | ThreeOfAKind, _ -> Win
        | _, ThreeOfAKind -> Lose

        | TwoPair, TwoPair ->
            let ranks1, ranks2 = (hand1.Cards, hand2.Cards) 
                                 |> Tuple.Map2 (PairRanks >> SortRanks)
            if ranks1 <> ranks2 then 
                let topRank1, topRank2 = ranks1.[0], ranks2.[0]
                let topPairOutcome = Outcome.FromRanks topRank1 topRank2
                if topPairOutcome <> Draw then
                    topPairOutcome
                else
                    let secondRank1, secondRank2 = ranks1.[1], ranks2.[1]
                    Outcome.FromRanks secondRank1 secondRank2
            else
                let kickers1, kickers2 = (hand1.Cards, hand2.Cards) |> Tuple.Map2 SoloRanks
                CompareKickers kickers1 kickers2
        | TwoPair, _ -> Win
        | _, TwoPair -> Lose

        | OnePair, OnePair ->
            let rank1, rank2 = (hand1.Cards |> PairRanks).[0], (hand2.Cards |> PairRanks).[0]
            if rank1 <> rank2 then 
                Outcome.FromRanks rank1 rank2
            else
                let kickers1, kickers2 = (hand1.Cards, hand2.Cards) |> Tuple.Map2 SoloRanks
                CompareKickers kickers1 kickers2
        | OnePair, _ -> Win
        | _, OnePair -> Lose

        | _, _ ->
            let kickers1, kickers2 = (hand1.Cards, hand2.Cards) |> Tuple.Map2 SoloRanks
            CompareKickers kickers1 kickers2