Thanks. There seems to be some consensus developing around using
IORefs to hold all the program state.
-- Jeff
On Fri, Feb 22, 2008 at 12:11 PM, Brandon S. Allbery KF8NH
On Feb 22, 2008, at 9:15 , Jefferson Heard wrote:
Now I'm to the point of making this thing interactive, and I I'm trying to figure out the Haskell way of doing this. Last time I wrote a program like this, I made a record data type with all the state and placed it into an IORef and curried it into the GLUT callback functions. I'm going to do the same thing now if there aren't cringes and wailings from people with a better sense of pure-functional aesthetics out there on the list with a willingness to either point me towards a tutorial that would help me do this better. Keep in mind that Graphics.UI.GLUT callbacks all want to return an IO (), and thus leftover state monads at ends of functions aren't going to be acceptable to the standard library...
What I do (with gtk2hs) is visible at http://hpaste.org/3137 --- MWPState is a fairly large record.
I will note that this code stores the mutable data in separate IORefs, whereas I'm told that it's better to use a single IORef with all the mutable state inside it. (For some reason I had assumed that the overhead would be higher.) That said, the wrappers make it fairly easy to refactor it. Since the IORef(s) and much of the remaining state is read-only, I use a ReaderT IO instead of StateT IO; this also turned out to be convenient for what turned out to be a significant optimization (in response to a timer firing, it collects a bunch of data and feeds it into a TreeView, and it turned out to be useful to collect it all at the front and use local to roll a modified record with the cached values).
(The code in that paste is rather out of date, probably I should update it.)
-- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allbery@kf8nh.com system administrator [openafs,heimdal,too many hats] allbery@ece.cmu.edu electrical and computer engineering, carnegie mellon university KF8NH
-- I try to take things like a crow; war and chaos don't always ruin a picnic, they just mean you have to be careful what you swallow. -- Jessica Edwards