Hi. Is this an appropriate place to report library bugs, or should I post to the various <implementation>-bugs lists instead? According to http://www.haskell.org/ghc/docs/latest/html/base/Control.Monad.Writer.html listens :: (MonadWriter w m) => (w -> w) -> m a -> m (a, w) but the inferred type is more general (and more useful) listens :: (MonadWriter w m) => (w -> b) -> m a -> m (a, b) Regards, Tom