On Wed, Nov 11, 2009 at 1:09 PM, Matthew Pocock <matthew.poc...@ncl.ac.uk> wrote: > 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?
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) -- Dave Menendez <d...@zednenem.com> <http://www.eyrie.org/~zednenem/> _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe