If you're afraid of Yampa (I was ;p), Ertugrul Söylemez released recently the Netwire library on hackage.
I went through its internals and I find it simpler to grasp and to use than Yampa as Ertugrul chose to replace the switch functions by the use of ArrowChoice. Yet I don't know if the latter wholly supersedes the former.
Plus I like the fact it doesn't depend on IO (you can handle automatons in pure code).

And if you're to stick with Yampa, you might wanna look at Animas.
It's a fork of Yampa. I don't the advantages it brings or what I changes, but its documentation on hackage is far more complete.

2011/12/27 Tim Baumgartner <baumgartner.tim@googlemail.com>
Hi Haskellers!

I'm writing my first non-trivial Haskell application. I have an electronic drum set that generates MIDI events that I process with Haskell. A simple application of this kind might have fixed drums associated with fixed commands (I've done that). The next step would be to display menus (with very large font...) that show commands and the associated drums. The menu structure should be derived from the commands active in each context. Up to this point, I implemented this already in Java. But now after some successful attempts in Haskell, I plan for more features: the user should ultimately be able to record his own "triggers", i.e. short drum rhythms, and associate them with actions. Since I'm still a beginner with only some basic experience in Monads, Arrows and their transformers, there is infinite knowledge to be gained by working on this problem (both library and concrete apps).

Currently I'm using a monad that combines Parsec (with MIDI event stream) and a Writer (that writes commands that should result in IO). It's done in a way that during running the monad, many parses can be done and failing parses roll back the parser state so that a new parse can be tried.

Now my questions:
I have read about Yampa, but I have not mastered it yet. E.g. I don't understand switches. Could my "triggers" be realized with Yampa's events and switches?
Would you recommend any other approach?
Is there something similar somewhere?

Regards
Tim


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