The issues with effect systems

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You can see what effects any block of code has.

That’s indeed useful, but you can have it in ReaderT-like approaches too. I wondered about that in this other thread.

Like, imagine that you have a record like

data Repository m = Repository
  { findById :: ResourceId -> m Resource,
    save :: Resource -> m ()
  }

And a constructor that uses a Has-like class to find its dependencies in a dependency injection environment:

makeRepository :: (Has Logger m deps, Has SomeOtherDep m deps) 
               => deps -> Repository m
makeRepository = undefined

That seems roughly analogous to an effectful interpreter for some Repository effect that delegates on the Logger and SomeOtherDep effects.

Maybe it’s a question of taste, but maybe there are other benefits in the effectful way.