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https://github.com/joefiorini/elm-time-machine
https://github.com/joefiorini/elm-time-machine
Last synced: 2 months ago
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- Host: GitHub
- URL: https://github.com/joefiorini/elm-time-machine
- Owner: joefiorini
- Created: 2015-01-12T04:56:38.000Z (about 10 years ago)
- Default Branch: master
- Last Pushed: 2018-02-12T23:04:47.000Z (almost 7 years ago)
- Last Synced: 2024-04-14T09:06:40.454Z (10 months ago)
- Language: Elm
- Size: 28.3 KB
- Stars: 6
- Watchers: 3
- Forks: 1
- Open Issues: 1
-
Metadata Files:
- Readme: README.md
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README
# Time Machine for Elm
It's like a Delorean for your state!
## What is it?
`elm-time-machine` is a library for the [Elm Programming Language](http://elm-lang.org) that tracks the history of your application's state, and contains a pointer letting you, in essence, travel backward or forward to some point in that state's timeline. It was written for the undo/redo functionality for [Flittal](http://flittal.com), a keyboard-driven flow charting tool, but should be general enough for anyone to use.
## Usage
Install with:
```
elm-package install joefiorini/elm-time-machine
```
Add a property to your state to hold the history:
```elm
type alias AppState =
{ contacts : List Contact
, history : TimeMachine.History (List Contact)
}
```
Initialize it in your default state:
```elm
defaultState =
{ contacts = []
, history = TimeMachine.initialize []
}
```
And then record entries whenever your state changes:
```elm
step update state =
case update of
AddContact contact ->
let contacts' = contact :: state.contacts
in
{ state | contacts <- contacts'
, history <- TimeMachine.record contacts'
}
```
To undo call `travelBackward`:
```elm
step update state =
case update of
Undo ->
let history' = TimeMachine.travelBackward state.history
in
case history'.current of
Just contacts' ->
{ state | contacts <- contacts'
, history <- history'
}
Nothing -> state
```
To redo call `travelForward`:
```elm
step update state =
case update of
Undo ->
let history' = TimeMachine.travelForward state.history
in
case history'.current of
Just contacts' ->
{ state | contacts <- contacts'
, history <- history'
}
Nothing -> state
```
Both of these functions will take you one step in either direction. Rather than returning the item, they return a new history record with the item in `current`. In the event that you travel all the way back to the beginning of time, you will get `Nothing`.
For more, see [the Elm package API docs](http://package.elm-lang.org/packages/joefiorini/elm-time-machine/1.0.0).
## Contributing
Write a test, run it, repeat. Run tests with:
```
cd test
make test
```
To automatically run tests when files change, first install daemontools and entr. On a Mac:
```
brew install daemontools
brew install entr
```
Neither of these tools will impact your development environment until you run them.
To start watching run:
```
cd test
supervise .
```
Feel free to open an issue or pull request if anything doesn't make sense.