Sudoku Solver in F#

open System

let input = 
    Array.map (fun _ -> Console.ReadLine().Split [| ' ' |]) [| 0 .. 8 |]
    |> Array.map (fun b -> Array.map (fun x -> Convert.ToInt32 (x:string)) b )

let display x = 
    x |> Array.iter (fun b -> 
                    Array.iter (fun x -> printf "%d " x) b; 
                    printfn "";
                 )
                 

let verify1 (grid:int[][]) x y c = 
    [0 .. 8] |> List.forall (fun i -> grid.[i].[y] <> c && grid.[x].[i]<> c)

let verify2 (grid:int[][]) x y c = 
          let xs = (x/3)*3 in
          let ys = (y/3)*3 in   
            [xs .. (xs+2)] |> List.forall (fun i -> 
                [ys .. (ys+2)] |> List.forall (fun j -> (grid.[i].[j] <> c)))

let verify grid x y c = 
    if (verify1 grid x y c) then (verify2 grid x y c) else false


let rec solve x y (grid:int[][]) =
   if grid.[x].[y] <> 0 then
      if (x = 8) && ( y = 8) then
         display grid
      else
         solve ((x+1) % 9) (if x = 8 then (y+1) else y) grid
   else
         [1..9] |> List.iter  (fun c ->
            if (verify grid x y c) then
               Array.set grid.[x] y c;
               solve x y grid;
            else
               ()
            Array.set grid.[x] y 0;
          )               
          
solve 0 0 input