Portability | non-portable (multi-param classes, functional dependencies) |
---|---|
Stability | experimental |
Maintainer | libraries@haskell.org |
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 whereSource
Methods
is an action that produces the output tell
ww
.
listen :: m a -> m (a, w)Source
is an action that executes the action listen
mm
and adds
its output to the value of the computation.
pass :: m (a, w -> w) -> m aSource
is an action that executes the action pass
mm
, which
returns a value and a function, and returns the value, applying
the function to the output.
listens :: MonadWriter w m => (w -> b) -> m a -> m (a, b)Source