mapWriter

mapWriter :: ((a, w) -> (b, w')) -> Writer w a -> Writer w' b
transformers Control.Monad.Trans.Writer.Lazy, transformers Control.Monad.Trans.Writer.Strict, mtl Control.Monad.Writer.Lazy, mtl Control.Monad.Writer.Strict
Map both the return value and output of a computation using the given function. *  (mapWriter f m) = f (runWriter >  
mapWriterT :: (m (a, w) -> n (b, w')) -> WriterT w m a -> WriterT w' n b
transformers Control.Monad.Trans.Writer.Lazy, transformers Control.Monad.Trans.Writer.Strict, mtl Control.Monad.Writer.Lazy, mtl Control.Monad.Writer.Strict
Map both the return value and output of a computation using the given function. *  (mapWriterT f m) = f > (runWriterT