Should RandomAccessList and PersistentVector be merged?

[rmunn]

While working on #54, I started to realize that the RandomAccessList data structure wasn't just similar to PersistentVector, it WAS a PersistentVector that simply iterated in reverse order, and when accessed by index, accessed the item at (count-1)-idx instead. This strikes me as unnecessary duplication of code. Why not just add one function to PersistentVector named reversedIterator, then implement RandomAccessList as something like this instead?

type RandomAccessList =
    inherit PersistentVector
    val lastIndex = count - 1
    override this.Item with get i =
        base.[lastIndex - i]
    override this.rangedIterator(startIndex, endIndex) =
        base.reversedIterator(lastIndex - startIndex, lastIndex - endIndex)
    override this.reversedIterator(startIndex, endIndex) =
        base.rangedIterator(lastIndex - startIndex, lastIndex - endIndex)
    override this.ofSeq items =
        // items |> Seq.rev |> base.ofSeq  // F# 4.0
        items |> List.ofSeq |> List.rev |> Seq.ofList |> base.ofSeq  // F# 3.1
    override this.Last = invalidOp "Can't take Last of a RandomAccessList"
    override this.Head = base.Last
    // etc., etc., etc.

(Note: the above is not valid F# code; I left out constructor parameters, generic types, and so on. Think of it as F# pseudocode).

The RandomAccessList module could stay pretty much the same, as most of its contents are simply calling the corresponding methods of the RandomAccessList type (or the RandomAccessList class, in C# terminology). But the duplication of code could be done away with.

[jackfoxy]

@rmunn this is a good idea, and since there are already unit tests in place, probably can be done safely (after reviewing unit tests for some comfort level of completion).

I would also be more comfortable seeing a BenchmarkDotNet comparison before and after of both collections, just to confirm it doesn't impact performance.

I would accept such a PR.

[jackfoxy]

I created RandomAccessList from @forki 's implementation of PersistentVector. I have a new found interest in RandomAccessList. I have found it is the ideal implementation of Vector in a project I am working on, so I am interested in bringing it up to date. I'm not interested in doing this code merge and interface myself. I will be adding functions to its module.