Do you see value in a Ref-Monad like State?

[rubenmoor]

I am using purescript for a canvas-based web app and don't need any fancy UI library. I end up with a lean, global application state and deal with events quite bare-footed.

I find myself writing

app <- read refAppState
flip write refAppState $
    app { foo = newFoo
        , bar = app.bar + 1
        }

quite a lot.

If you don't object, I'll come up with a pull request soon to allow to write the above via a monad for effectfull, global state:

foo .= newFoo
bar += 1

I miss the lenses :)

Also, maybe you have a suggestion for the module name.

How about Effect.Ref.Monad? Alternatively Control.Monad.State.Global.

[hdgarrood]

I think something along these lines is unlikely to be merged in this library; we prefer to keep core libraries as lean and unopinionated as is reasonably possible. Are you imagining something that is more or less equivalent to newtype RefM s m a = RefM (StateT (Ref s) m a)? Because I don't think that needs to exist; why not just use StateT directly?

[rubenmoor]

Putting a reference into a local state (StateT (Ref s) m a or State (Ref s) a) doesn't make sense. What you mean is probably ReaderT (Ref s) m a or Reader (Ref s) a. That still would imply explicit use of write and read from Effect.Ref and does not allow anything close to the syntax above. Correct me if I'm wrong.

[hdgarrood]

Yes, you're right, I did mean Reader rather than State. But in any case I don't think this is something we will want to include in this library.

[rubenmoor]

My initial idea is complicated by the fact that a reference-based, global state monad, being effectful, cannot have an instance of the type-class MonadState, which is of course pure.

The only way out that I can see would be to re-implement an effectful variant of MonadState. This, in turn, implies a re-implementation of all related lenses. A huge copy-and-paste, might still be somewhat useful, but by no means elegant.