Reactive-banana 1.0 monadic API: How to define recursive behavior now?

Question

In a reactive banana <1.0.0 this worked:

-- takes a start value, minimum and maximum value, flag whether counter is
-- cyclic, an increment and decrement event stream and returns a behavior
mkCounter :: (Enum a,Ord a) => a -> Maybe a -> Maybe a -> Bool
          -> Event t b -> Event t c -> Behavior t a
mkCounter start minVal maxVal cyclic incE decE = counter
  let incF curr | isNothing maxVal = succ
                | Just maxv <- maxVal, curr<maxv = succ
                | Just maxv <- maxVal, Just minv <- minVal, cyclic = const minv
                | otherwise = id
      decF curr | isNothing minVal = pred
                | Just minv <- minVal, curr>minv = pred
                | Just minv <- minVal, Just maxv <- maxVal, cyclic = const maxv
                | otherwise = id
  counter = accumB start $ ((incF <$> counter) <@ incE) `union`((decF <$> counter) <@ decE)

Now counterdefined in terms of oneself. But in the new monadic API it accumBis a monadic function, and it is here that I don’t see how to act - it Momentdoes not have an instance MonadFix, since this works now?

For obvious reasons, this does NOT work ("Not in scope: counter")

mkCounter :: (MonadMoment m,Enum a,Ord a) => a -> Maybe a -> Maybe a -> Bool
          -> Event b -> Event c -> m (Behavior a)
mkCounter start minVal maxVal cyclic incE decE = do
  -- .. same as above ..
  counter <- accumB start $ unions [((incF <$> counter) <@ incE)
                                   ,((decF <$> counter) <@ decE)]
  return counter

What is the right way to do it now? Thanks in advance!

Answer 1

, . MonadFix m , Moment Monad:

mkCounter :: (MonadFix m,MonadMoment m,Enum a,Ord a) => a -> Maybe a -> Maybe a -> Bool
          -> Event b -> Event c -> m (Behavior a)

mdo.