Remove the `attribute` type parameter

[upsiflu]

• 23

Proposal A: Hide the attribute type parameter which affects the Link element rendering, and make it default to Html.Attribute msg

Proposal B: Introduce a type parameter linker analogous to wrapper, and in Layout, add a field link : linker -> html.

Proposal C: Replace the type parameter wrapper with a combined wrapper/linker that accepts either:

• a lifecycle marker: Inserted | Removable | Removed
• a custom wrapper: Node String (List Attribute) | Ul (List Attribute) |...
• a Link and link config: Link (List Attribute) {isInline, label}

wrapOrLink : WrapperOrLinker -> List html -> List html
wrapOrLink wrapperOrLinker children =
    case wrapperOrLinker of
         Inserted -> ...
         ...
         Link attrs { url : String } -> [ a [ href url ] children ]
         Switch attrs { url : String, isChecked : Bool } -> [ Html.a ( Attr.href url :: Attr.aria-checked isChecked :: attrs ) children ]
         Node tag attrs -> Html.node tag attrs
         ...

The layout would connect Link and Switch via Link:

type alias Link.Elements attribute wrapper =
    { link : List attribute -> (\{ url : String } -> wrapper)
    , switch : List attribute -> (\{ url : String, isChecked : Bool }  -> wrapper)
    }
myElements =
    { link = Link, switch = Switch }

and then you's write `toggle []...

No! Instead,

type MyWrapper attribute label
= Inserted
| ...
| TextLink (List attribute) { label : String }
| ...

and then we

NO!

Here is correct:

We name it Style and then in layout, we say wrap : Style -> html -> html, link : Style -> {url, label} -> html, switch : Style -> {url, label, isChecked} -> html :-) :-) :-)

Disadvantage: The only use case where one would want to use a different attribute type to draw links than Html.Attribute Never is if you use elm-w3 (a package that makes Html nodes and attributes as strict as the w3c spec). In that case, each element (a and area are the only elements that allow hrefs) needs to have the same attribute type anyways. So instead, we force total composability around links, even when that would violate the w3 spec.

Advantage: Removing attribute simplifies the code

Discussion:

• If there is a significant use case for Html.Attribute msg, then I'd prefer to parametrize Ui over msg instead.
• If we want to support elm-w3, we need to support nested type narrowing

Implementation:

• [x] Delete the attribute type parameter
• [x] Extend the wrapper type parameter to handle Element

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