The Observer pattern http://github.com/gimbo/observer.hs
|Latest on Hackage:||0.0.1|
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This is a Haskell implementation of the Observer design pattern [1,2],
providing a typeclass and an example implementation (Synchronous)
which is perfectly usable in its own right.
This package is based on Observable.hs by Bastiaan Heeren ,
originally published as part of an exercise  for his students. It
has been modified, extended and packaged by Andy Gimblett [5,6].
* Implement a mechanism for removal of observers. Consider Tom
Lokhorst's suggestion on haskell-cafe .
2009.11.11 v0.0.1 - first release, renamed from observer to
simple-observer in recognition that there are more
sophisticated ways to skin this particular cat.
2009.10.30 v0.0.0 - first Cabalised version, unreleased.
 Gamma et al: `Design Patterns: Elements of Reusable
Object-Oriented Software', Addison-Wesley, 1994.