WriterT -transformers

WriterT :: m (a, w) -> WriterT w a
mtl Control.Monad.Writer.Lazy, mtl Control.Monad.Writer.Strict
execWriterT :: Monad m => WriterT w m a -> m w
transformers Control.Monad.Trans.Writer.Lazy, transformers Control.Monad.Trans.Writer.Strict, mtl Control.Monad.Writer.Lazy, mtl Control.Monad.Writer.Strict
Extract the output from a writer computation. *  m = liftM snd > (runWriterT  
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  
runWriterT :: WriterT w a -> m (a, w)
mtl Control.Monad.Writer.Lazy, mtl Control.Monad.Writer.Strict