| Copyright | (c) Andy Gill 2001, (c) Oregon Graduate Institute of Science and Technology, 2001 |
|---|---|
| License | BSD-style (see the file LICENSE) |
| Maintainer | libraries@haskell.org |
| Stability | experimental |
| Portability | non-portable (multi-param classes, functional dependencies) |
| Safe Haskell | Safe-Inferred |
| Language | Haskell98 |
Control.Monad.Writer.Class
Description
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.
- class (Monoid w, Monad m) => MonadWriter w m | m -> w where
- listens :: MonadWriter w m => (w -> b) -> m a -> m (a, b)
- censor :: MonadWriter w m => (w -> w) -> m a -> m a
Documentation
class (Monoid w, Monad m) => MonadWriter w m | m -> w where
Methods
writer :: (a, w) -> m a
writer (a,w)
tell :: w -> m ()
tell ww.
listen :: m a -> m (a, w)
listen mm and adds
its output to the value of the computation.
pass :: m (a, w -> w) -> m a
pass mm, which
returns a value and a function, and returns the value, applying
the function to the output.
Instances
| MonadWriter w m => MonadWriter w (MaybeT m) | |
| MonadWriter w m => MonadWriter w (IdentityT m) | |
| MonadWriter w m => MonadWriter w (StateT s m) | |
| MonadWriter w m => MonadWriter w (StateT s m) | |
| MonadWriter w m => MonadWriter w (ReaderT r m) | |
| (Error e, MonadWriter w m) => MonadWriter w (ErrorT e m) | |
| (Monoid w, Monad m) => MonadWriter w (WriterT w m) | |
| (Monoid w, Monad m) => MonadWriter w (WriterT w m) | |
| (Monoid w, Monad m) => MonadWriter w (RWST r w s m) | |
| (Monoid w, Monad m) => MonadWriter w (RWST r w s m) |
listens :: MonadWriter w m => (w -> b) -> m a -> m (a, b)