gistfile1.fs

let binarySearch value (array: 'T[]) =
    let rec loop lo hi =
        if lo <= hi then
            let mid = lo + ((hi - lo) >>> 1)
            match array.[mid] with
            | x when x = value -> Some mid
            | x when x < value -> loop (mid + 1) hi
            | _ -> loop lo (mid - 1)
        else None
    loop 0 (array.Length - 1)