Tail

let (|Tail|_|) xs ys =
    let xl, yl = Array.length xs, Array.length ys
    let mutable i = 0
    while i < xl && i < yl && xs.[i] = ys.[i] do i <- i + 1
    if i = xl then Some(Array.sub ys xl (yl-xl))
    else None

let xs = [|1 .. 5|]

match xs with
| Tail [|1;2;3|] tail -> tail
| _ -> [||]