- liftIO $ atomically
- $ do oldState ← readTVar $ itrState itr
- if newState < oldState then
- throwStateError oldState newState
- else
- do let a = [oldState .. newState]
- b = tail a
- c = zip a b
- mapM_ (uncurry $ drift itr) c
- writeTVar (itrState itr) newState
+ liftIO $ atomically $ driftTo' itr newState
+
+driftTo' ∷ Interaction → InteractionState → STM ()
+driftTo' itr@(Interaction {..}) newState
+ = do oldState ← readTVar itrState
+ if newState < oldState then
+ throwStateError oldState newState
+ else
+ do let a = [oldState .. newState]
+ b = tail a
+ c = zip a b
+ mapM_ (uncurry drift) c
+ writeTVar itrState newState