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Make HTML functions return Doc, have extra Elt.x functions that return Elt #183

Tarmil opened this Issue Jul 12, 2018 · 2 comments


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Tarmil commented Jul 12, 2018

With the hindsight from using UI in many applications, I've come to the conclusion that:

  • The vast majority of use cases for DOM elements do not make any use of Elt-specific APIs like .Dom, .OnEvent, .AppendDoc, etc and could just as well have type Doc.

  • There are many situations where we need to upcast from Elt to Doc, which is more verbose than necessary.


    • Branches with different types:

      if someCondition then
          span [] [text "test"] :> Doc
    • Higher-order functions:

      let mkList (count: int) (generate: int -> Doc) =
          ul [] [for i in 1..count do yield li [] [generate i]]
      let elt = mkList 10 (fun i -> span [] [text (string i)] :> Doc)
    • Lists that the compiler would otherwise mistakenly think are heterogeneous:

          span [] [text "haha"] :> Doc
    • yield (this one will apparently be fixed in F# 4.5):

      div [] [
          yield span [] [text "test"] :> Doc
          if someCondition then
              yield a [attr.href "/"] [text "test"] :> Doc

I therefore propose that:

  • Functions such as div, span, etc from the WebSharper.UI.Html module should return type Doc instead of Elt.
  • A new module WebSharper.UI.Html.Elt should be added, with these same functions returning Elt.

Obviously this is a breaking change, but I think it's a worthwile one that will both make learning easier and real-life code more readable.

Note that this only concerns the F# API; C# performs enough automatic upcasting that this is not problematic there.

@Tarmil Tarmil added the proposal label Jul 12, 2018


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cata commented Jul 12, 2018

@Tarmil I'm all for it. I can't think of one single case where we use Elt-specific APIs in our code. on the other hand, upcasts from Elt to Doc are pervasive.


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Tarmil commented Aug 7, 2018

Change applied in 6be098a.

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