How to express conditionally present element in a list?

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1

I’m building a page with elm-ui (the most recent one) where I have a couple of floating elements that may or may not appear depending on certain conditions.
I express this with a list of inFront attributes for the layout element. For now I make them appear and disappear by swapping them the inFront content with Element.none, like so

  [ 
        --...
        , Element.inFront
            (if model.toSave then
                Element.el [ Element.alignBottom, Element.centerX ]
                    (Element.Input.button [] { onPress = Nothing, label = Element.el [] <| Element.text "Save" })
             else
                Element.none
            )
        -- ...
        ]

However I can’t say I’m satisfied with this solution; it looks ugly and hard to read. Can I get some suggestions on how to make it better?

2

First: I normally use qualified imports, but not for elm-ui code:

        , inFront
            (if model.toSave then
                el [ alignBottom, centerX ]
                    (Input.button [] { onPress = Nothing, label = el [] <| text "Save" })
             else
                none
            )

Looks less ugly already…
You can also create yourself a helperfunction:

renderIf : Bool -> Element msg -> Element msg
renderIf condition content =
  if condition then 
    content 
  else 
    none

So that your code looks something like this:

        , inFront <| renderIf model.toSave <|
              el [ alignBottom, centerX ]
                    (Input.button [] { onPress = Nothing, label = el [] <| text "Save" })
3

A somewhat similar problem is discussed in this thread.
You may check to see if any of those ideas are acceptable.

4

I would extract the if model.toSave ... portion out to another top level function. Something like viewSaveButton : { a | toSave : Bool } -> Element Msg or possibly viewSaveButton : Bool -> Element Msg. Then your parent element is

...
    [ Element.inFront (viewSaveButton model)
    , Element.inFront  (viewOtherElement model)
    , ...
    ]

For me, moving chunks of code to a top level function is a great way to help with readability. I often do this with the children of my elements to.

5

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