Elm AMR

Automatic message-replay for Elm!

This module records messages that are passed to the update-function during development, and automatically replays them when the program is reloaded:

• All messages up until the first unrecognized will be replayed - This mitigates jarring app-states that could otherwise cause confusion during development.
• There is currently no built-in way to reinitialize this kind of program, which means changes to commands sent from init won't be picked up. One way around this is to open the developer-console in the browser, and type localStorage.clear(), assuming you're using localStorage for persistance.

The API requires a few functions:

1. Encode messages to JSON
2. Decode messages from JSON
3. Read JSON-encoded messages from flags
4. Write JSON-encoded messages to an outgoing port
5. A tiny script in your HTML to pick up port-output, persisting it somehow

A tiny example can be found here.

Design

On top the stuff described above, this module addresses some of the performance-issues related to recording every single interaction with your application:

• Messages are encoded exactly once each, mapped to an integer, and then added to an array of integers that represent the sequence of messages update received. Integer-arrays with a mapping from integer to message should be more space-efficient than storing encoded messages directly (and redundantly).
• Every new message is pre-encoded, when update is called, to speed up cache-writes.

Future Plans

I plan to have message-encoding/decoding be code-generated using static-analysis, distributed as a small CLI/API on NPM.