Why MonadWriter instance for ChronicleT uses underlying monad

[mutantmell]

ChronicleT seems like it can be made a valid MonadWriter, without relying on the underlying monad.

If it is not, it should be documented.

[mutantmell]

This seems to be a valid instance of MonadWriter:

instance (Monoid c, Semigroup c, Monad m) => MonadWriter c (ChronicleT c m) where
    tell = dictate

    listen (ChronicleT m) = ChronicleT $ do
      a <- m
      case a of
        This  x   -> return $ This x
        That    y -> return $ These mempty (y, mempty)
        These x y -> return $ These x (y, x)

    pass (ChronicleT m) = ChronicleT $ do
      a <- m
      case a of
        This  x       -> return $ This x
        That    (a,f) -> return $ These (f mempty) a
        These x (a,f) -> return $ These (f x) a

    writer (a,w) = ChronicleT $ return $ These w a

[phadej]

MonadReader or MonadWriter ?

[mutantmell]

MonadWriter, sorry

[phadej]

Let's see what will be answered in http://stackoverflow.com/questions/41096328/why-monadreader-r-statet-s-m-uses-an-instance-of-the-underlying-monad

Related to #67