ringbuffer.fs

type RingBuffer<'a> = private {
    buffer: 'a option array
    size: int
    index: int
}

module RingBuffer =
    open System

    let create size = {
        buffer = Array.create size None
        size = size
        index = -1
    }

    let pop () ring =
        if ring.index = -1 then
            (None, ring)
        else
            let value = Array.get ring.buffer ring.index

            let buffer = Array.copy ring.buffer
            Array.set buffer ring.index None

            let size = Math.Max(0, ring.size - 1)
            let index =
                if size = 0 then
                    - 1
                elif ring.index = 0 then
                    Array.length ring.buffer
                else
                    ring.index - 1

            let ring = {
                buffer = buffer
                index = index
                size = size
            }

            (value, ring)

    let push value ring =

        let buffer = Array.copy ring.buffer
        let bufferLength = Array.length ring.buffer
        let index =
            if ring.index + 1 >= bufferLength then
                0
            else
                ring.index + 1

        Array.set buffer index (Some value)

        let size = Math.Min(ring.size + 1, bufferLength)

        {
            buffer = buffer
            index = index
            size = size
        }

let ring =
    RingBuffer.create 2
    |> RingBuffer.push 1
    |> RingBuffer.push 2
    |> RingBuffer.push 3
    |> RingBuffer.push 4
    |> RingBuffer.push 5
    |> RingBuffer.pop ()
    |> snd
    |> RingBuffer.push 7

printfn "%A" ring