[Haskell-cafe] adding state in GUIs (qtHaskell)

Michael P Mossey mpm at alumni.caltech.edu
Wed Sep 9 21:58:23 EDT 2009

Been poking around. Maybe IORef has something to do with this? I found a 
qtHaskell example that seems to make use of IORef in order to accomplish 
something similar to what I want.

Michael P Mossey wrote:
> I'm trying to learn qtHaskell. I realize few people on this list know 
> anything about qtHaskell, but I have a question that probably relates to 
> all GUIs as implemented in Haskell. I just need a hint that could help 
> me figure out the next step, which I might be able to infer from the 
> qtHaskell API.
> I don't think is any tutorial-type or step-by-step type documentation 
> for qtHaskell. I have sent some questions to the author of qtHaskell, 
> David Harley, but he hasn't responded yet, and anyway I don't want to 
> trouble him every time I have a question, so I'm trying to infer as much 
> as I can.
> The problem relates to state. In Qt, one adds state to a widget by 
> subclassing it and adding new member variables. For example, I want to 
> create a widget that responds to keypresses and remembers what 
> keypresses have taken place.
> I'm totally stuck on this part, because Haskell doesn't have state. 
> There must be some kind of Haskell call that adds state to a widget, but 
> it is hard to figure out from the qtHaskell examples David provides.
> Thanks,
> Mike
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