https://github.com/Fresheyeball/elm-return

Writer powered pipelining for `(model, Cmd msg)`
https://github.com/Fresheyeball/elm-return

Last synced: 13 days ago
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Writer powered pipelining for `(model, Cmd msg)`

• Host: GitHub
• URL: https://github.com/Fresheyeball/elm-return
• Owner: Fresheyeball
• License: bsd-3-clause
• Created: 2016-06-11T03:18:49.000Z (over 8 years ago)
• Default Branch: master
• Last Pushed: 2022-09-26T12:18:34.000Z (about 2 years ago)
• Last Synced: 2024-05-21T01:07:09.597Z (6 months ago)
• Language: Elm
• Homepage:
• Size: 11.2 MB
• Stars: 82
• Watchers: 4
• Forks: 4
• Open Issues: 5
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

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README

        
# Return

When writing Elm code you unavoidably have to interact with types like this:

```elm

( model, Cmd msg )

```

This library makes that a Type:

```elm

type alias Return msg model =

    ( model, Cmd msg )

```

You can interact with `Return` in terms of the `Model`, and trust that `Cmd`s

get tracked and batched together automatically. Letting you focus on composing

transformations on `Return` without manually shuffling around `Cmd`.

## Examples

Lets say we have a situation where we have a top level `update` function

and wish to embed a component's `update` function.

```elm

type Model

    = HomeMod Home.Model

    | AboutMod About.Model

type Msg

    = HomeMsg Home.Msg

    | AboutMsg About.Msg

update : Msg -> Model -> (Model, Cmd Msg)

update msg model =

    let

        (updateModel, updateCmd) =

            case (model, msg) of

                (HomeMod model_, HomeMsg msg_) ->

                    let

                        (subModel, subCmd) =

                            Home.update msg_ model_

                    in

                    ( HomeMod subModel, Cmd.map HomeMsg subCmd )

                (AboutMod model_, AboutMsg msg_) ->

                    let

                        (subModel, subCmd) =

                            About.update msg_ model_

                    in

                    ( AboutMod subModel, Cmd.map AboutMsg subCmd )

                x ->

                    let

                        _ =

                            Debug.log "Stray found" x

                    in

                    ( model, Cmd.none )

       transformed =

          Route.alwaysTranfromModelWithMe updateModel

    in

    ( transformed

    , Cmd.batch

        [ updateCmd

        , alwaysDoMeCmd

        , conditionallyDoSomething transformed

        ]

    )

```

The code above is good, but it suffers in some areas. For example

we could forget to include `updateCmd` in the final `in` expression,

and those side effects are lost. Or we could neglect to put the

final *third* version of the model, `transformed`, into `conditionallyDoSomething`.

That and there is a big dependence on pattern matching and literals,

which does not lend itself well to pipelining.

Lets see how we can clean this up with `Return`.

```elm

type Model

    = HomeMod Home.Model

    | AboutMod About.Model

type Msg

    = HomeMsg Home.Msg

    | AboutMsg About.Msg

update : Msg -> Model -> Return Msg Model

update msg model =

    (case (model, msg) of

        ( HomeMod model_, HomeMsg msg_ ) ->

              Home.update msg_ model_

                  |> mapBoth HomeMsg HomeMod

        ( AboutMod model_, AboutMsg msg_ ) ->

              About.update msg_ model_

                  |> mapBoth AboutMsg AboutMod

        x ->

            let

                _ =

                    Debug.log "Stray found" x

            in

                singleton model)

    |> command alwaysDoMeCmd

    |> map Route.alwaysTranfromModelWithMe

    |> effect_ conditionallyDoSomething

```

The cleaned up code is not only more succinct, and more imperative (in a good way),

but it doesn't suffer from the problems described above. There is no risk of mixing up

your terms or accidentally dropping a cmd.