timbuckley / count

Call record constructors with increasing integers. Surprisingly useful!

Count

This was created to manage things like tabIndex and z-index. Here's how we might manage some z-index values manually:

layers =
    { normal = 1
    , dropdown = 2
    , menu = 3
    , modal = 4
    }

We might use it like so:

div
    [ class "menu"
    , style [ ( "z-index", toString layers.menu ) ]
    ]
    [ text "menu goes here" ]

This works, but if we want to add a new layer in the middle, or reorder any of the existing layers, we have to redo all the numbering by hand.

Using Count

Count offers a nicer alternative:

type alias Layers =
    { normal : Int
    , dropdown : Int
    , menu : Int
    , modal : Int
    }


layers =
    Count.to4 Layers

In both examples, the value of layers is the same.

In the second one, reordering the fields in the type alias causes them to be renumbered automatically. Adding a fifth field necessitates only swapping out Count.to4 for Count.to5.

This works just as well for tabIndex.

Getting map involved

Let's say you want to transform each of the numbers before passing it along. Maybe you want them to start from 0 instead of 1, which you could accomplish by counting to 5 and then subtracting 1 from each value. Maybe you also want to turn them into strings so you can pass them to style without having to call toString on them every time.

Here's how you'd do that:

    type alias Layers =
        { normal : String
        , dropdown : String
        , menu : String
        , overlay : String
        , modal : String
        }


    layers : Layers
    layers =
        Count.mapTo5 (\num -> toString (num - 1)) Layers

    {-

        { normal = "0"
        , dropdown = "1"
        , menu = "2"
        , overlay = "3"
        , modal = "4"
        }

    -}

That's it!

That's the whole library.