Messages based on Commands are not fed into stream

Hey Dag,

I am trying to use Elmish Stream in the Safe Confplanner and I am banging my head for the last couple of hours because it is not working as (I) expected.

In the Confplanner I need to work with commands (so no mksimple) and I have a couple of situations where I need to create messages from commands within the update function. For this I am using the elmish Cmd.OfFunc.result MyMsg et al functions. It seems that those message are never fed into the message stream (it is somehow circumvented and the messages go directly into update). Is this expected behaviour? I can create a minimal repro but I wanted check first if this is the way it is supposed to be.

[dbrattli]

Yes, I get the point. I’ll look into it.

[johannesegger]

@bender2k14 not directly. With streams I don’t use Cmds at all. update has the signature 'msg -> 'model -> 'model instead of 'msg -> 'model -> 'model * Cmd<'msg>. The side effects that are usually performed by Cmds are now performed as part of the stream. Mocking those side effects - e.g. in tests - might become harder but I consider those tests to be too trivial to create anyway (probably an unpopular opinion).

I found that the coupling between a state update and deciding what side-effect to perform sometimes makes things unnecessarily complicated (e.g. throttling/debouncing is not trivial with Cmds but built into streams).