On Thu, Nov 12, 2009 at 8:01 AM, Matthew Pocock
Yes. This bit me the first time I came across it. I think we need a Control.Monad.State.StrictOnState with strict behaviour on the state value. I notice this same underlying issue is coming up in more than one thread on these lists.
This monad would indeed be useful, however it may be confusing as well. For example, if you are inserting elements in a Map using a lazy insert, seq'ing the map will only reduce it to WHNF (of course) and move the insertion down one level in the tree. IOW, I'd guess that OP's problem can't be solved just by seq'ing the map, he would have to use strict operations. There's a strict insertWith in Data.Map, but IIRC it's strict only on its combining operation, not on the insertion itself. Hmmm... maybe Control.Monad.State.RnfOnState? =P Cheers, -- Felipe.