Fable.Elmish.Nile

Extension to Fable.Elmish that enables transforming the stream of dispatched messages from the view to messages that are dispatched to the update function.

It's an alternative approach to Fable.Elmish.Streams. However Fable.Elmish.Streams has some nice helpers that you might want to use with Fable.Elmish.Nile.

Sample usage:

open Fable.Elmish.Nile

let stream states msgs =
    [
        // Let `Increment` messages flow through.
        // Note that messages are swallowed by default, you have to explicitely let them flow through.
        msgs
        |> AsyncRx.choose (function | Increment as x -> Some x | _ -> None)

        // Debounce `Search` messages for 500 ms
        msgs
        |> AsyncRx.choose (function | Search as x -> Some x | _ -> None)
        |> AsyncRx.debounce 500
    ]
    |> AsyncRx.mergeSeq // Merge all streams together (this is where "Nile" comes from)

Program.mkSimple init update view
|> Program.withStream stream
|> Program.run

Sub streams are also possible:

open Fable.Elmish.Nile

let stream states msgs =
    [
        // Top-level message
        msgs
        |> AsyncRx.choose (function | ActivateTab _ as x -> Some x | _ -> None)

        // Forward model and message stream to sub component and map the resulting messages back to top-level messages
        (
            states |> AsyncRx.map (snd >> fun m -> m.SubComponent1Model),
            msgs |> AsyncRx.choose (function SubComponent1Msg msg -> Some msg | _ -> None)
        )
        ||> SubComponent1.stream
        |> AsyncRx.map SubComponent1Msg

        // The pattern for sub components is always the same
        (
            states |> AsyncRx.map (snd >> fun m -> m.SubComponent2Model),
            msgs |> AsyncRx.choose (function SubComponent2Msg msg -> Some msg | _ -> None)
        )
        ||> SubComponent2.stream
        |> AsyncRx.map SubComponent2Msg
    ]
    |> AsyncRx.mergeSeq // Merge all streams together (this is where "Nile" comes from)

Program.mkSimple init update view
|> Program.withStream stream
|> Program.run