Solution to the Zebra Puzzle in F# as shown at the Zurich F# Users Meetup group

zebra.fs

//http://en.wikipedia.org/wiki/Zebra_Puzzle
// Zebra Puzzle
//
//1 There are five houses.
//
//2 The Englishman lives in the red house.
//
//3 The Spaniard owns the dog.
//
//4 Coffee is drunk in the green house.
//
//5 The Ukrainian drinks tea.
//
//6 The green house is immediately to the right of the ivory house.
//
//7 The Old Gold smoker owns snails.
//
//8 Kools are smoked in the yellow house.
//
//9 Milk is drunk in the middle house.
//
//10 The Norwegian lives in the first house. 
//
//11 The man who smokes Chesterfields lives in the house next to the man with the fox.
//
//12 Kools are smoked in a house next to the house where the horse is kept.
//
//13 The Lucky Strike smoker drinks orange juice.
//
//14 The Japanese smokes Parliaments.
//
//15 The Norwegian lives next to the blue house.
//
//Who drinks water? Who owns the zebra?
//
//Each house is painted a different color, and their inhabitants are of different nationalities, own different pets, drink different beverages and smoke different brands of American cigarettes.

namespace ZebraDemo

module programOrdered =

    let rec permutations inputlist taken = 
      seq { if Set.count taken = List.length inputlist then yield [] else
            for l in inputlist do
              if not (Set.contains l taken) then 
                for perm in permutations inputlist (Set.add l taken)  do
                  yield l::perm }

    let myperms = permutations [1;2;3] Set.empty
    Seq.length myperms 
    Seq.toList myperms 

    let splitToTuple = function
        | [fst; sec; thrd; fth; ffth] -> (fst, sec, thrd, fth, ffth)
        | _ -> failwith "wrong list format"

    let nextTo (frst, sec) =
        frst - 1 = sec || frst + 1 = sec

    let myHouses = [1..5]

    let myHousePerms = permutations myHouses Set.empty
    Seq.length myHousePerms

    let myOrderedAnswer = 
        [for myCountryList in myHousePerms do    
            let (England, Spain, Ukraine, Japan, Norway) = splitToTuple myCountryList
            if Norway = 1 then
                for myColorList in myHousePerms do
                    let (red, green, ivory, yellow, blue) = splitToTuple myColorList
                    if  England = red && 
                        green - 1 = ivory &&
                        nextTo (Norway, blue) then
                            for myDrinkList in myHousePerms do
                                let (coffee, tea, milk, oj, WATER) = splitToTuple myDrinkList
                                if  Ukraine = tea &&
                                    green = coffee &&
                                    milk = 3 then
                                    for  mySmokeList in myHousePerms do
                                        let (oldGold, kools, chesterfields, luckyStrike, parliaments) = splitToTuple mySmokeList
                                        if  yellow = kools &&
                                            luckyStrike = oj &&
                                            Japan = parliaments then
                                                for myPetList in myHousePerms do
                                                    let (dog, snail, horse, fox, ZEBRA) = splitToTuple myPetList
                                                    if      Spain = dog && 
                                                            oldGold = snail &&
                                                            nextTo(chesterfields, fox) &&
                                                            nextTo(kools, horse) then
                                                            yield [("red", red); ("green", green); ("ivory", ivory); ("yellow", yellow); ("blue", blue);
                                                                    ("England", England); ("Spain", Spain); ("Ukraine", Ukraine); ("Japan", Japan); ("Norway", Norway);
                                                                    ("coffee", coffee); ("tea", tea); ("milk", milk); ("oj", oj); ("WATER", WATER);
                                                                    ("dog", dog); ("snail", snail); ("horse", horse); ("fox", fox); ("ZEBRA", ZEBRA);                                     
                                                                    ("oldGold", oldGold); ("kools", kools); ("chesterfields", chesterfields); ("luckyStrike", luckyStrike);  ("parliaments", parliaments)] ]




    let ans = List.head myOrderedAnswer
    
    let selectFromList houseNum = 
        List.filter (fun (fst, snd) -> snd = houseNum) ans
        |> List.map (fun (fst, snd) -> fst)


    printfn "house 1:"
    printfn "%A" (selectFromList 1)
    printfn "house 2:"
    printfn "%A" (selectFromList 2)
    printfn "house 3:"
    printfn "%A" (selectFromList 3)
    printfn "house 4:"
    printfn "%A" (selectFromList 4)
    printfn "house 5:"
    printfn "%A" (selectFromList 5)