Free monads

Hi everyone. I'll follow Simon's lead, and ask a similar question with a similar motivation. I'm going to talk about free monads at the upcoming Haskell eXchange next Wednesday. I'll not limit myself to a particular library, and I'm open to related approaches (e.g. "operational") as well. I'm also looking for as many compelling examples as possible. Like Simon, I don't want to know anything secret or anything that you wouldn't like me to include in my talk. Most useful are pointers to existing libraries using free monads that I might have missed (for example, because they're new or very specialized). Thanks a lot for your help in advance. Cheers, Andres -- Andres Löh, Haskell Consultant Well-Typed LLP, http://www.well-typed.com