Re: [Haskell-cafe] Long running Haskell program

On Wed, Nov 11, 2009 at 10:29 AM, David Menendez wrote:

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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

On Wed, Nov 11, 2009 at 1:09 PM, Matthew Pocock wrote: the

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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?

I think replacing "put s" with "put $! s" should guarantee that the state is evaluated.

If you're using get and put in many place in the code, you could try something along these lines:

newtype SStateT s m a = S { unS :: StateT s m a } deriving (Monad, etc.)

instance (Monad m) => MonadState s (SStateT s m) where get = S get put s = S (put $! s)

That's interesting, and once I have time to come back to this part of the project (I was behind schedule at this point!) I'll try something like that.

-- Dave Menendez http://www.eyrie.org/~zednenem/ _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe