Removing the 'dispatch' function from the view function

Having now spent some time playing with Fabulous (and really enjoying using it!) I became curious as to why the update function requires the dispatch function to be passed in which is a little different to Elm. Apologies if there is a well know design reason for it and please let me know if there is!

Fabulous

model : 'model
update : 'msg -> 'model -> 'model
view : 'model -> ('msg -> unit) ->  ViewElement

Elm

model : Model
update : Msg -> Model -> Model
view : Model ->  Html Msg

When starting with Fabulous it seemed a little odd to have this parameter and it seems Jamie was confused. From looking through the code I think its there to ensure type safety for the commands on the ViewElements? This lead me to think could ViewElement be defined as ViewElement<'msg> in something like the following pseudo code:

type ViewElement<'msg> = 
    { text : string
      command : 'msg option 
      children : ViewElement<'msg> list option }
    member x.Create() : obj = new obj()
    member x.UpdateIncremental(prev: ViewElement<'msg>, target: obj) : unit = ()

type View() =
    static member inline Button<'msg> (text: string, command : 'msg) = { text = text; command = Some command; children = None }
    static member inline Label (text: string) = { text = text; command = None; children = None }
    static member inline ContentPage (children : ViewElement<'msg> list) = { text = ""; command = None; children = Some children }

    type Model = { Count : int }
    type Msg = Increment
    let init () = { Count = 0 }

    let update (msg : Msg) (model : Model) : Model =
        match msg with 
        | Increment -> { model with Count = model.Count + 1 }

    let view (model : Model) =
        View.ContentPage(
            children =
                [ View.Label(text = string model.Count)
                  View.Button(text = "Increment", command = Increment)])

    let program = mkSimple init update view

This constrains the command to all be of type Msg and would give the classic elm architecture of:

model : 'model
update : 'msg -> 'model -> 'model
view : 'model ->  ViewElement<'msg>

Not sure if this is possible or desirable but I thought I would ask the question?

[et1975]

Just adding 2c: if I had control over view DSL (as Fabulous does), I’d have avoided passing dispatch explicitly. This has nothing to do with Elmish (which still needs to pass the dispatch into whatever renderes the view) and everything to do with the DSL that was available to implement Elmish.React. If you look at the issue it is still on my mind.

[TimLariviere]

v2 removes dispatch from the view function 😃