Is it ok to store sink inside the model?

[functora]

I need to emit action on some async events like loading files from input component:

https://github.com/functora/functora.github.io/blob/4ca33c655deea34117e27b5feb2a03f13c432c96/ghcjs/miso-functora/src/Functora/Miso/Widgets/Field.hs#L344-L350

Because my input component is basically just a view, I need to make two things - create main application miso action, and emit async event which should land on update function of the main miso application. I'm using two corresponding arguments of my input component to do so:

https://github.com/functora/functora.github.io/blob/4ca33c655deea34117e27b5feb2a03f13c432c96/ghcjs/miso-functora/src/Functora/Miso/Widgets/Field.hs#L35-L36

Providing action argument is easy - basically it's just a mapping to main miso application action type. Providing emitter argument is a bit less straightforward, because my input component is basically a view, so all argument I'm providing I should get somehow from the model, because I don't have direct access to main miso app update function, effectSub and sink.

The workaround I'm using at the moment is to save MVar with the sink to the model on the initial main miso app update, so I can have access to it from my input component:

https://github.com/functora/functora.github.io/blob/4ca33c655deea34117e27b5feb2a03f13c432c96/ghcjs/delivery-calculator/src/Main.hs#L124-L125

Is it ok to do so, or there are better ways to emit async actions from components similar to my input component? Best regards!

[dmjio]

This isn't a bad idea per se. There really isn't a good way (that I see yet) to expose the global sink to users outside of the update function.

One alternative (so you can keep the model pure) is to do the {-# NOINLINE #-} unsafePerformIO trick to make the sink global.

globalSinkRef :: IORef (Sink Action)
{-# NOINLINE globalSinkRef #-}
globalSinkRef = unsafePerformIO $ newIORef (\_ -> pure ())

update InitGlobalSink m = 
  effectSub m $ \sink -> 
    m <# liftIO (writeIORef globalSinkRef sink)

Then you can just do readIORef globalSinkRef to get the sink from any IO action w/o polluting your model. Hope this helps.

Lastly, IORef should be fine over MVar, since the concurrency is handled internally, shouldn't need MVar necessarily.

TBH, we could add this to the library and users could make use of it exactly for circumstances like this.

[dmjio]

#751

[functora]

Thanks @dmjio !

[dmjio]

Yea let me know how it works out for you