Concise F# version of Conway's Game of Life

F# Game of life

(*
    F#  Game of life

    Philip Jander 
    @ph_j
    2015

    This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License.
    https://creativecommons.org/licenses/by-nc-sa/3.0/
*)

module GameOfLife =

    let private rng = new System.Random()
    let random_cells (rx,ry) number = set [ for x in 1..number -> (rng.Next rx),(rng.Next ry) ]

    let private printcell (x,y) =
        if (x>=0 && y>=0 && y<=30 && x<=30) then
            System.Console.SetCursorPosition(x,y)
            System.Console.Write("#")

    let print board =
        System.Console.Clear()
        board |> Set.iter printcell

    let private envelope1 (x,y) = set [ for dx in -1..+1 do for dy in -1..+1 -> (x+dx,y+dy) ]
    let private envelope = Set.map envelope1 >> Set.unionMany
    let private active_neighbors cells cell = Set.intersect cells (envelope1 cell) |> Set.remove cell |> Set.count
    let private cells_with_active_neighbors number active area = area |> Set.filter (fun cell -> (active_neighbors active cell) = number)
    let step cells = Set.union (cells_with_active_neighbors 2 cells cells) (cells_with_active_neighbors 3 cells (envelope cells))

let rec main board : unit =
    GameOfLife.print board
    GameOfLife.step board |> main

main (GameOfLife.random_cells (20,20) 50)

And yes, I know Console.Clear is not great performance.
That wasn't the point ;)

Ruby's still faster ;)