gol.fs

type Cell = int * int

let exists_in element =
  Seq.exists ((=) element)

let vicinity (x, y) =
  seq {
    for px in -1..1 do
    for py in -1..1 do
    yield (x+px, y+py)
  } |> Seq.filter (fun c -> c <> (x,y))

let shouldSurvive (world: Cell seq) (cell : Cell, ns) =
  match ns with
  | 3 -> true
  | 2 when exists_in cell world -> true
  | _ -> false

let next world =
  let world' = world |> Seq.toList
  world'
  |> Seq.collect vicinity
  |> Seq.groupBy id
  |> Seq.map (fun (k, v) -> (k, Seq.length v))
  |> Seq.filter (shouldSurvive world')
  |> Seq.map fst

let glider = seq {
    yield (2, 0)
    yield (2, 1)
    yield (2, 2)
    yield (1, 2)
    yield (0, 1)

    // Line
    yield (20, 3)
    yield (20, 4)
    yield (20, 5)
}

let display world =
    System.Console.SetCursorPosition(0,0)
    seq {
        for x in 1..26 do
        for y in 1..25 do
        yield (x,y)
    }
    |> Seq.mapi (fun i c ->
        match c with
        | c when exists_in c world -> printf "X"
        | _ when (i % 25) = 0 -> printf "\n"
        | _ -> printf "."
    )
    |> ignore

seq { 1 .. 100 } 
|> Seq.fold ( fun world _ ->
    display world
    System.Threading.Thread.Sleep(200)
    next world
) glider
|> ignore