Acid-state: MonadState instance for Update

Question

I\'m trying acid-state. The documentation states that Update st is an instance of MonadState st. I tried different things, but my comp

Answer 1

Ok, I finally solved it.

The issue was with two different mtl versions installed. Hiding the wrong one fixed everything.

The interesting part is how I got it :)

Prelude Data.Acid Control.Monad.State> :i Update
newtype Update st a
  = acid-state-0.6.4:Data.Acid.Common.Update {acid-state-0.6.4:Data.Acid.Common.unUpdate :: transformers-0.2.2.0:Control.Monad.Trans.State.Lazy.State
                                                                                              st a}
    -- Defined in `acid-state-0.6.4:Data.Acid.Common'
instance Monad (Update st)
  -- Defined in `acid-state-0.6.4:Data.Acid.Common'
instance Functor (Update st)
  -- Defined in `acid-state-0.6.4:Data.Acid.Common'
Prelude Data.Acid Control.Monad.State>

Control.Monad.State reexports State, but you can see that ghci still shows transformers-0.2.2.0:Control.Monad.Trans.State.Lazy.State fully qualified.