Queue.LfrQueue - unexpected size after adding same item twice

[Janiczek]

I'm not sure this is expected (are you not allowed to enqueue the same item twice?)

Minimal example:

empty |> enq 0 |> enq 0 |> size
--> 3

Trying it out in elm-repl:

> import Queue.LfrQueue exposing (..)
> empty |> enq 0 |> enq 0 |> size
3 : Int
> empty |> enq 0 |> enq 0
([0],[0,0]) : Queue number
>

The test that found this:

fuzz (Fuzz.list Fuzz.int) "empty+enq+size: behaves like stdlib queue" <|
    \items ->
        let
            lfrQueue =
                List.foldl enq empty items

            stdlibQueue =
                List.foldl (::) [] items
        in
        size lfrQueue
            |> Expect.equal (List.length stdlibQueue)

[Janiczek]

I'm guessing this should use front and rear once each instead of using front twice https://github.com/amenzwa/pfd/blob/main/src/Queue/LfrQueue.elm#L34

[amenzwa]

Martin, Okasaki's Standard ML implementation for left-right queue (which he calls BatchedQueue) on p.43 is fun snoc ((f, r), x) = checkf (f, x::r), which I mistranslated into Elm as enq x ( f, r ) = checkF ( f, x :: f ). The correct translation is enq x ( f, r ) = checkF ( f, x :: r ). I just fixed this bug, and updated the test case, too.

Thank you so much for finding this bug.