Every time when a message triggers. The update function applies twice but because of distinctUntilRefChanged operator the second model doesn't emit to the downstream.
Minimal, Reproducible Example
The example in the repository is prone to this issue.
Steps to Reproduce
Just add a trace to the update function to reveal the function call.
update :: Message -> Model -> Model
update = case _ of
Increase -> trace "increase" (\_ -> (_ + 1))
Decrease -> (_ - 1)
Expected Behavior
On each message the update function should just be called once.
Actual Behavior
2x call of update function on each message.
Browsers Affected
[x] Chrome
[x] Firefox
[x] Edge
[x] Safari 11
[x] Safari 10
[x] IE 11
Versions
Monarch: v0.0.0
Etiology
The issue is because the eModel is an Event not a Queue (BTW we should choose a better name for it :|). Each time when we subscribe to the eModel event it adds a subscriber to qMessage queue and each subscriber will be called separately.
Description
Every time when a
messagetriggers. The update function applies twice but because ofdistinctUntilRefChangedoperator the secondmodeldoesn't emit to the downstream.Minimal, Reproducible Example
The example in the repository is prone to this issue.
Steps to Reproduce
Just add a
traceto theupdatefunction to reveal the function call.Expected Behavior
On each
messagetheupdatefunction should just be called once.Actual Behavior
2x call of
updatefunction on eachmessage.Browsers Affected
Versions
Etiology
The issue is because the
eModelis anEventnot aQueue(BTW we should choose a better name for it :|). Each time when we subscribe to theeModelevent it adds a subscriber toqMessagequeue and each subscriber will be called separately.https://github.com/the-dr-lazy/purescript-monarch/blob/403bcfa4030ff4a9f707ca15c824b196c2f298d1/src/Monarch/Platform.purs#L126-L127
Solution
The
eModelevent should be convert to a queue.