On Tue, Dec 20, 2011 at 11:08 AM, Michael Serra <mk.se...@gmail.com> wrote: > Hello Haskellers, > I'm implementing a simple tree-manipulating (for sports tournaments) > application prototype, with SDL for graphics and simple user interaction. > For reference, I've posted the code on hpaste. My question is about code > organization: everything was simple and elegant until I started writing the > program's display/event loop. Every function in this section has to be > passed the same parameters - the application window to draw on, the font to > display text with, the tree representing the current application state, > etc. The font is an especially egregious example of the problem, because > it's only used by one function but to get there it must be threaded through > all of them (looking at the hpaste, you will see I don't want to call > openFont on every invocation of drawTexts; what's needed is to call it once > in main and have the resulting value available to drawTxt. So my question: > how can I mitigate the ugliness of this state-threading? I understand this > is one purpose for monads; am I supposed to implement a monad transformer > for this? > > I think it would be great if I could define a type AppState as a tuple of > the various things I need to thread, and specify some kind of automatic > as-pattern, so that every function taking this AppState parameter would > implicitly have its components bound to certain preset names. I've never > seen anyone do this however. What is the right solution? >
I've done that before in web-apps. It is conventional enough. To ease the threading-through of paramters you can use a Reader monad (perhaps ReaderT AppState IO). I don't know how well this fits in with the SDL libraries, though. Antoine > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
