-- Hoogle documentation, generated by Haddock
-- See Hoogle, http://www.haskell.org/hoogle/


-- | The Observer pattern
--   
--   This is a simple Haskell implementation of the Observer pattern,
--   specified as a typeclass with one example instance (demonstrating
--   synchronous notifications). It is based on Observable.hs by Bastiaan
--   Heeren, originally from
--   <a>http://www.cs.uu.nl/wiki/bin/view/Afp0607/ExerciseWXHaskell</a>
@package simple-observer
@version 0.0.1


-- | An implementation of the Observer pattern, based on Observable.hs by
--   Bastiaan Heeren, originally from
--   <a>http://www.cs.uu.nl/wiki/bin/view/Afp0607/ExerciseWXHaskell</a>
--   
--   This module defines the <a>Subject</a> typeclass, specifying the
--   capabilities of an observable value. See other modules in the package
--   for example implementations of this typeclass.
module Control.Observer

-- | A type class for observable objects. A minimal implementation
--   implements all of these functions.
class Subject sub val | sub -> val
getValue :: Subject sub val => sub -> IO val
setValue' :: Subject sub val => sub -> val -> IO ()
addObserver :: Subject sub val => sub -> (val -> IO ()) -> IO ()
getObservers :: Subject sub val => sub -> IO [val -> IO ()]

-- | Update the subject value, and notify observers.
setValue :: Subject sub val => sub -> val -> IO ()

-- | Notify observers that the subject's value has changed. Rarely called
--   explicitly: usually called via <a>setValue</a>.
notifyObservers :: Subject sub val => sub -> IO ()

-- | Apply an update function to the subject value, and notify observers.
changeValue :: Subject sub val => sub -> (val -> val) -> IO ()

-- | Add an observer which doesn't care about the subject's value, only
--   that it's changed.
addConstObserver :: Subject sub val => sub -> IO () -> IO ()


-- | A synchronous implementation of the <a>Subject</a> typeclass, , based
--   on Observable.hs by Bastiaan Heeren, originally from
--   <a>http://www.cs.uu.nl/wiki/bin/view/Afp0607/ExerciseWXHaskell</a>
--   
--   The <a>Subject</a> implementation defined in this module uses
--   <a>MVar</a>s to provide a simple and threadsafe synchronous
--   implementation of the Observer design pattern.
--   
--   Note that no constructor for <a>Sub</a> is exported: client code must
--   use the <a>createSub</a> smart constructor.
module Control.Observer.Synchronous

-- | Threadsafe synchronous Subject implementation.
data Sub a

-- | Smart constructor for Sub.
createSub :: a -> IO (Sub a)
instance Subject (Sub a) a