This page covers Elm 0.18

Plan

The plan for changing a player's level is as follows:

(1) When the user clicks the increase or decrease button we trigger a message ChangeLevel with the playerId and howMuch as payload.

(2) Html.program (which Navigation wraps) will send this message back to Main.Update which will route it to Players.Update (3).

(4) Players.Update will return a command to save the player, this command flows up to Html.program (5).

(6) The Elm runtime executes the command (trigger an API call) and we will get a result back, either a succesful save or a failure. In the success case we trigger a SaveSuccess message with the updated player as payload.

(7) Main.Update routes the SaveSuccess message to Players.Update.

(8) In Players.Update we update the players model and return it. This flows back to Html.program (9).

(10) Then Html.program will render the application with the updated model.