F# Binary Search

gistfile1.fs

module ChrisMcKelt
open System
open System.ServiceModel
open Microsoft.FSharp.Linq
open Microsoft.FSharp.Data.TypeProviders
open System.Linq

let rec chop (arr:array<int>, low:int, high:int, value:int) =
    if (high < low) then
        null
    else
        let mid = (low + high) / 2
        if (value > arr.Length) then
           box None
        else
            if (arr.[mid] > value) then
                chop (arr, low, mid-1, value)
            else if (arr.[mid] < value) then
                chop (arr, mid+1, high, value)
            else
                match box arr.[mid] with
                    | null -> box None
                    | x -> box(Some(x))


[<EntryPoint>]
let main argv = 
    let list = [1..10000]
    let findme = 7777
    let arr = Array.ofList list
    let result = chop(arr, list.Head, list.Last(),findme)
        
    Console.WriteLine(result)
    Console.WriteLine("Press any key to continue...");
    Console.ReadLine() |> ignore
    0 // return an integer exit code