writer package:monads-tf

The MonadWriter class. Inspired by the paper /Functional Programming with Overloading and Higher-Order Polymorphism/, Mark P Jones (http://web.cecs.pdx.edu/~mpj/pubs/springschool.html) Advanced School of Functional Programming, 1995.

type Writer w = WriterT w Identity

monads-tf Control.Monad.Writer.Lazy Control.Monad.Writer.Strict

A writer monad parameterized by the type w of output to accumulate. The return function produces the output mempty, while >>= combines the outputs of the subcomputations using mappend.

newtype WriterT w (m :: Type -> Type) a

monads-tf Control.Monad.Writer.Lazy Control.Monad.Writer.Strict

A writer monad parameterized by:

w - the output to accumulate.
m - The inner monad.

The return function produces the output mempty, while >>= combines the outputs of the subcomputations using mappend.

WriterT :: m (a, w) -> WriterT w (m :: Type -> Type) a

monads-tf Control.Monad.Writer.Lazy Control.Monad.Writer.Strict

class (Monoid (WriterType m), Monad m) => MonadWriter m

monads-tf Control.Monad.Writer.Class Control.Monad.Writer.Lazy Control.Monad.Writer.Strict

execWriter :: Writer w a -> w

monads-tf Control.Monad.Writer.Lazy Control.Monad.Writer.Strict

Extract the output from a writer computation.

```
execWriter m = snd (runWriter
m)
```

execWriterT :: Monad m => WriterT w m a -> m w

monads-tf Control.Monad.Writer.Lazy Control.Monad.Writer.Strict

Extract the output from a writer computation.

execWriterT m = liftM snd
(runWriterT m)

mapWriter :: ((a, w) -> (b, w')) -> Writer w a -> Writer w' b

monads-tf Control.Monad.Writer.Lazy Control.Monad.Writer.Strict

Map both the return value and output of a computation using the given function.

runWriter (mapWriter f m) = f (runWriter
m)

mapWriterT :: (m (a, w) -> n (b, w')) -> WriterT w m a -> WriterT w' n b

monads-tf Control.Monad.Writer.Lazy Control.Monad.Writer.Strict

Map both the return value and output of a computation using the given function.

runWriterT (mapWriterT f m) = f
(runWriterT m)

runWriter :: Writer w a -> (a, w)

monads-tf Control.Monad.Writer.Lazy Control.Monad.Writer.Strict

Unwrap a writer computation as a (result, output) pair. (The inverse of writer.)

runWriterT :: WriterT w (m :: Type -> Type) a -> m (a, w)

monads-tf Control.Monad.Writer.Lazy Control.Monad.Writer.Strict