effect-handlers (hackage): This is an extensible effects library for Haskell taking inspiration from the Eff language http://www.eff-lang.org/.  See these papers for the ideas and theory behind the library:  O. Kammar et al: Handlers in Action! http://homepages.inf.ed.ac.uk/slindley/papers/handlers.pdf  A. Bauer, M. Pretnar: Programming with Algebraic Effects and Handlers http://arxiv.org/abs/1203.1539  O Kiselyov, A Sabry, C Swords: Extensible Effects http://dl.acm.org/citation.cfm?id=2503791  Implementation wise it's most close to extensible-effects http://hackage.haskell.org/package/extensible-effects (also see the Extensible Effects paper) but it implements deep handlers instead of shallow.
Keywords: control|library|mit