https://github.com/bowbahdoe/elm-history

A History Data Structure for the Elm Programming Language
https://github.com/bowbahdoe/elm-history

datastructure elm frontend

Last synced: 7 days ago
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A History Data Structure for the Elm Programming Language

• Host: GitHub
• URL: https://github.com/bowbahdoe/elm-history
• Owner: bowbahdoe
• License: apache-2.0
• Created: 2019-02-24T07:08:08.000Z (over 5 years ago)
• Default Branch: master
• Last Pushed: 2019-03-18T15:34:08.000Z (over 5 years ago)
• Last Synced: 2023-08-08T20:38:16.941Z (over 1 year ago)
• Topics: datastructure, elm, frontend
• Language: Elm
• Size: 11.7 KB
• Stars: 2
• Watchers: 3
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

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README

        
# elm-history

This library provides a data structure for managing the "History"

of some values. It is useful for making features that are along

the lines of undo and redo. 

[Try it on Ellie][1]

[1]: https://ellie-app.com/52ctv8T5Q2Sa1

```elm

module Main exposing (main)

import Browser exposing (sandbox)

import History exposing (History)

import Html exposing (Html, br, button, div, text)

import Html.Events exposing (onClick)

type alias Model =

    History Int

type Msg

    = Increment

    | Decrement

    | TimesFive

    | Redo

    | Undo

init : Model

init =

    History.new 0

update : Msg -> Model -> Model

update msg model =

    case msg of

        Increment ->

            History.to (History.current model + 1) model

        Decrement ->

            History.to (History.current model - 1) model

        TimesFive ->

            History.to (History.current model * 5) model

        Undo ->

            History.back model

        Redo ->

            History.forward model

view : Model -> Html Msg

view model =

    div []

        [ text (String.fromInt (History.current model))

        , br [] []

        , button [ onClick Increment ] [ text "Increment" ]

        , br [] []

        , button [ onClick Decrement ] [ text "Decrement" ]

        , br [] []

        , button [ onClick TimesFive ] [ text "Time Five" ]

        , br [] []

        , button [ onClick Redo ] [ text "Redo" ]

        , br [] []

        , button [ onClick Undo ] [ text "Undo" ]

        ]

main =

    sandbox { init = init, update = update, view = view }

```