mapPositionsT :: (Monad m, Monad n) =>
                 (m a -> n b) -> PositionsT m a -> PositionsT n b
mapPositionsT f = PositionsT . mapReaderT f . unpackPositionsT
mapPositionsT :: (Monad m, Monad n) =>
                 (m a -> n b) -> PositionsT m a -> PositionsT n b
mapPositionsT f = PositionsT . mapReaderT f . unpackPositionsT
mapPositionsT f = PositionsT . mapReaderT f . unpackPositionsT