Re: [Haskell-cafe] Long running Haskell program

Is there a state monad that is strict on the state but lazy on the computation? Of course, strictness in the state will force a portion of the computation to be run, but there may be significant portions of it which are not run. Would there be a way to write a state monad such that it is entirely lazy, but then to wrap either the computation or the state in an 'eager' strategy datatype which takes care of this in a more flexible manner? Thanks, Matthew 2009/11/11 Bryan O'Sullivan

On Wed, Nov 11, 2009 at 7:43 AM, David Leimbach wrote:

...

I recently ran into some serious space leak difficulties that would ultimately cause this program to crash some time after startup (my simulator is also written in Haskell, and runs a LOT faster than the real application ever could, this has enabled me to fast forward a bit the data growth issues and crash in minutes instead of days!)

It sounds to me like you were storing a Map in a StateT. Since the usual State and StateT monads don't force the evaluation of their payload, I'm not terribly surprised that such a leak should arise.

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