[Haskell-cafe] GUI and background processing

Dmitry V'yal akamaus at gmail.com
Mon Jun 1 08:24:36 EDT 2009

Greetings, fellow haskellers.

Currently I'm writing some kind of web crawler in haskell with gtk2hs gui.

All network operations are run in separate thread, but sometimes input 
from user is needed. Afaik, gtk2hs is not thread safe, so I came up with 

I create two mvars, A and B, one for question, one for answer. Worker 
thread puts question in A and blocks trying to take B. Gui thread checks 
for question by polling with tryTakeMVar. Then question is ready, it 
asks user and puts his answer into B. Worker awakens and continues 

Also, for progress report, I use a Chan which is written to by worker 
and is read by polling by gui thread.

This scheme works, but I don't like it. All these mvars and chans create 
too much clutter, and polling looks rather ugly too. Is there a better 
way for implementing similar patterns of interaction?

Best regards,

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