F# Immutable variable sized window data structure

Question

I have below a description of a data structure I need and I want to implement it using immutable data structures. I\'m trying to determine... is there an existing data struc

Answer 1

Without knowing more about your requirements, I'd just say a vanilla Set<'a> does a more than adequate job. I'd prefer a 'Set' over a 'List' so you always have O(lg n) access to the largest and smallest items, allowing you to ordered your set by insert date/time for efficient access to the newest and oldest items.

Seems very easy to wrap up a set so that its Add/Remove methods invoke your callbacks:

type AwesomeSet(internalSet : Set<'a>, insertCallback : 'a -> unit, removeCallback : 'a -> unit) =
    member this.Add(x) =
        insertCallback(x)
        AwesomeSet(internalSet.Add x, insertCallback, removeCallback)

    member this.Remove(x) =
        removeCallback(x)
        AwesomeSet(internalSet.Remove x, insertCallback, removeCallback)

    member this.Count = internalSet.Count
    member this.Min = internalSet.MinimumElement
    member this.Max = internalSet.MaximumElement