Conway's Game of Life in F#

Question

Since I'm learning F# along with functional programming, I managed to implement the rules for Conway's Game of Life. I'm not sure if I can improve some of its parts, though. For example, the neighbours function does an ugly range testing, but I can't think of anything simpler.

module Game
open System
type Cell =
 | Alive
 | Dead
let amount_neighbours (board: Cell[,]) (pos: int * int) =
 let range (n: int) (limit: int) = 
 let min = if n < 1 then 0 else n - 1
 let max = if n > (limit - 2) then (limit - 1) else n + 1
 [min .. max]
 let x_range = range (fst pos) (Array2D.length1 board)
 let y_range = range (snd pos) (Array2D.length2 board)
 List.sum [for x in x_range ->
 List.sum [for y in y_range -> if board.[x, y] = Alive && (x, y) <> pos then 1 else 0]]
let lifecycle (board: Cell[,]) = 
 Array2D.init (Array2D.length1 board) (Array2D.length2 board) (fun i j ->
 let neighbours = amount_neighbours board (i, j)
 match neighbours with
 | 2 -> board.[i, j]
 | 3 -> Alive
 | _ -> Dead)
let rec process_game (board: Cell[,]) (n: int) =
 match n with
 | x when x > 0 -> 
 printfn "Iteration"
 printfn "%A" board
 process_game (lifecycle board) (n - 1)
 | _ -> 0
[<EntryPoint>]
let main args =
 let board = Array2D.init 5 5 (fun i j -> if i = 2 && j > 0 && j < 4 then Alive else Dead)
 ignore (process_game board 4)
 0

Answer 1

I thought it would make sense if you created a function alive, which would take care of bounds checking for you. And also simplify the the final expression by using a single sequence expression instead of two like you do.

But I'm not sure it's actually much better than your version:

let amount_neighbours (board: Cell[,]) (pos: int * int) =
 let alive board pos = 
 let (x, y) = pos
 if x < 0 || x >= Array2D.length1 board ||
 y < 0 || y >= Array2D.length2 board then
 false
 else
 board.[x, y] = Alive
 let vicinity x = seq { x - 1 .. x + 1 }
 seq {
 for x in vicinity (fst pos) do
 for y in vicinity (snd pos) do
 if (x, y) <> pos && alive board (x, y) then
 yield true
 } |> Seq.length

• viniciushana: Well, this is a good improvement IMO. I'll vote up as soon as I can! Thanks.