Have you tried to compile your code with optimisations? I guess GHC's strictness analysis would find strict evaluation is better here.


2012/1/30 Joey Hess <joey@kitenet.net>
Claude Heiland-Allen wrote:
> Control.Monad.State.Strict is strict in the actions, but the state
> itself is still lazy, so you end up building a huge thunk in the
> state containing all the updates that ever took place to the initial
> state.
>
> Using this should fix it:
>
> modify' :: MonadState s m => (s -> s) -> m ()
> modify' f = do
>   x <- get
>   put $! f x  -- force the new state when storing it

Thanks!

So, why does Control.Monad.State.Strict.modify not do that?

And, I still don't quite understand why this only happened
when the updated value is obtained using IO.

--
see shy jo

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