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I think it wouldn't be hard to do an Eq instance for Ref right? Would you be open to a pull request?

Preempted by purescript/purescript-st#4:

modifySTRef :: forall a h r. STRef h a -> (a -> a) -> Eff (st :: ST h | r) a
modifyRef   :: forall s   r.   Ref   s -> (s -> s) -> Eff (ref :: REF | r) Unit

In particular the current behavior of modifyRef' strangely returns an arbitrary value not what's stored.

I think it would be good to export uncurried variants of the operations for cases where we want to forgo the overhead of currying.

I've bumped into a few cases where it would be really handy to be able to construct a Ref outside of Eff - it seems to me that reading and writing a ref are definitely effectful, but creating one isn't necessarily so. Thoughts?

Quick question on the type of new. Why does it have the type new :: forall s. s -> Effect (Ref s) instead of new :: forall s. s -> Ref s? I see no effects happening in the code.

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.

Mimicing Lens:

(.=) = writeRef
(%=) = modifyRef
(%%=) = modifyRef`

In practice looks like:

nextEvent counter payload = do
  count <- getRef counter
  counter %= (_ + 1)
  pure (Event (payload {id = count}))

Just wondered if it might be generally useful?

The function passed to newWithSelf should not read or write to the reference it's passed, though it may create closures that will eventually do so. This restriction is not documented.