Evening,
I'm trying to write a utility that reads in some user preferences from a pre-determined file, does some work, and exits. Sounds simple enough.
The problem I'm having is with the preferences: How do I make it available throughout the entire program? (FWIW, most of the work is effectively done inside the IO monad.) I could explicitly pass the record around everywhere, but that seems a trifle inelegant.
My current solution is to use a global ('scuse my terminology, I'm not sure that's the right word to use here) variable of type IORef Config obtained through unsafePerformIO. It works, but strikes me as a rather barbaric solution to a seemingly tame enough problem...
Intuition tells me I should be able to `embed', if you will, the config record somehow within or alongside the IO state, and retrieve it at will. (Is this what MonadState is for?) However it also tells me that this will /probably/ involve lots of needless lifting and rewriting of the existing code, which makes it even less enticing than passing everything around explicitly.
This is how I usually do it: http://www.mail-archive.com/haskell@haskell.org/msg10565.html (ignore the last part of the post...) J.A.