David Menendez wrote:
Floptical Logic wrote:
The code below is a little interactive program that uses some state. It uses StateT with IO to keep state. My question is: what is the best way to generalize this program to work with any IO-like monad/medium? For example, I would like the program to function as it does now using stdin but I would also like it to function over IRC using the Net monad from http://haskell.org/haskellwiki/Roll_your_own_IRC_bot. Thanks for any suggestions.
Instead of specifying the monad implementation, specify the interface. That is, you are using state operations (from MonadState) and IO operations (from MonadIO). Try removing all the type signatures that mention PDState and see what you get.
E.g., loop :: (MonadState PD m, MonadIO m) => m a
Alternatively, you can use algebraic data types instead of type classes to generalize one program to different implementations. For monads, this can be achieved with http://hackage.haskell.org/package/MonadPrompt In particular, the idea is to turn every effect like getLine into a constructor GetLine and have different implementations pattern match on that. Regards, apfelmus -- http://apfelmus.nfshost.com