On Sat, Nov 19, 2011 at 6:08 PM, Tim Baumgartner
I have not yet gained a good understanding of the continuation monad, but I wonder if it could be used here. What would a clean solution look like? Perhaps there are other things that need to be changed as well?
Your 'Interaction' data type is actually an instance of the more general "operational monad" (as named by Heinrich Apfelmus) or "prompt monad" (as named by Ryan Ingram). You will ready-to-use implementations on the packages MonadPrompt [1] and operational [2,3]. Reading their documentation you'll find some links about the development of these concepts. MonadPrompt uses a Cont-style implementation, while operational uses a simple abstract data type together with a viewing function that avoids O(n²) behavior. If you find it hard to describe your 'Interaction' using operational (easiest to use package, IMO), please send us another e-mail. Cheers! [1] http://hackage.haskell.org/package/MonadPrompt [2] http://hackage.haskell.org/package/operational [3] http://heinrichapfelmus.github.com/operational/Documentation.html -- Felipe.