how to chain Cmd Msgs

Question

I have a list of Cmd Msgs that need to be run in order. I\'m currently using Cmd.batch list but it seems like all of them are running simultaneousl

Answer 1

Task.sequence will ensure that the tasks run in sequence rather than simultaneously.

To make a Cmd msg from a task, you use Task.attempt or Task.perform.

Edit

Based on your updated question, I don't think there is a real need to use Tasks for this. It sounds like you want to chain a bunch of updates together, and that can be done by having the update function call itself recursively. You could use List.foldl to accumulate the model state and commands for each subsequent message.

Here's a quick and dirty example of what I mean:

update msg model =
  case msg of
    ChainMsgs msgs ->
      let
        chain msg1 (model1, cmds) =
          let (model2, cmds1) = update msg1 model1
          in model2 ! [ cmds, cmds1 ]
      in
        List.foldl chain (model ! []) msgs
    _ ->
      { model | message = model.message ++ ", " ++ toString msg } ! []

You are guaranteed that the messages are passed to update in the correct order, because there's no need to wrap it in tasks which makes order of execution ambiguous.

Here is a gist of this quick 'n dirty example which you can paste directly into http://elm-lang.org/try: