Even simpler, Freezer could just be a Monad denoting arbitrary "cleanup" actions, as long as they don't involve writes. -- | A computation that is guaranteed to run after all modifications are complete. newtype Freeze s a = {- private constructor and accessor -} Freeze { getFreeze :: ST s a } deriving (Functor, Applicative, Monad) freezeArray :: (Ix i, MArray a e (ST s), IArray b e) => a i e -> Freeze s (b i e) freezeArray arr = Freeze (unsafeFreeze arr) -- Reads are fine too, just not writes freezeRef :: STRef s a -> Freeze s a freezeRef ref = Freeze (readSTRef ref) runSTFreeze :: (forall s . ST s (Freeze s a)) -> a runSTFreeze act = runST (act >>= getFreeze) The proposed -Trav and -With functions can be implemented straightforwardly from that if desired: runSTArrayTrav m = runSTFreeze (m >>= traverse freezeArray) runSTUArrayTrav m = runSTFreeze (m >>= traverse freezeArray) runSTArrayWith tr m = runSTFreeze (m >>= tr freezeArray freezeArray) On Wed, Aug 21, 2019 at 11:46 PM Henning Thielemann < lemming@henning-thielemann.de> wrote:
On Wed, 21 Aug 2019, Zemyla wrote:
The "runSTArray" and "runSTUArray" functions allow efficiently working with Arrays in the ST monad before turning them immutable
I think instead of some new functions we should have a Kleisli Arrow data type that hides unsafeFreeze for us.
newtype Freezer s a b = -- private constructor and accessor Freezer {getFreezer :: a -> ST s b}
instance Category Freezer where instance Arrow Freezer where
quickFreeze :: Freezer s (STArray s i e) (Array i e) quickFreeze = Freezer unsafeFreeze
runFrozen :: (forall s. Freezer s a b) -> (forall s. ST s a) -> b runFrozen freezer st = runST (getFreezer (freezer st))
For moving two arrays and an additional value out, you would do
runFrozen ((quickFreeze *** quickFreeze) *** id) st _______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries