Strict version of Data.Map.map
Hi, Is it possible to write a strict version of Data.Map.map (so that the Map becomes strict in the elements as well as the keys)? Thanks, Edsko
I'd advise you to see Control.Parallel.Strategies, specially the NFData class and the rnf function. HTH, -- Felipe.
On Thu, Feb 26, 2009 at 12:45:09PM -0300, Felipe Lessa wrote:
I'd advise you to see Control.Parallel.Strategies, specially the NFData class and the rnf function.
What is the time complexity of running rnf on a Data.Map? If it is O(n), then surely running rnf on my map after every 'map' operation is hardly going to speed things up? Edsko
On Thu, Feb 26, 2009 at 2:13 PM, Edsko de Vries
On Thu, Feb 26, 2009 at 12:45:09PM -0300, Felipe Lessa wrote:
I'd advise you to see Control.Parallel.Strategies, specially the NFData class and the rnf function.
What is the time complexity of running rnf on a Data.Map? If it is O(n), then surely running rnf on my map after every 'map' operation is hardly going to speed things up?
I guess so. Maybe using mapAccum helps: import qualified Data.Map as M strictMap :: (a -> b) -> M.Map k a -> M.Map k b strictMap f m = case M.mapAccum f' () m of ((), m') -> m' where f' () x = x' `seq` ((), x') where x' = f x testStrictness mapper = m `seq` "Not strict." where m = mapper (const e) (M.singleton () ()) e = error "Strict!" :: () Testing: *Main> testStrictness M.map "Not strict." *Main> testStrictness strictMap "*** Exception: Strict! Don't know about efficiency, though :). HTH, -- Felipe.
I guess so. Maybe using mapAccum helps:
import qualified Data.Map as M
strictMap :: (a -> b) -> M.Map k a -> M.Map k b strictMap f m = case M.mapAccum f' () m of ((), m') -> m' where f' () x = x' `seq` ((), x') where x' = f x
testStrictness mapper = m `seq` "Not strict." where m = mapper (const e) (M.singleton () ()) e = error "Strict!" :: ()
Very clever. I had tried to use mapAccum but I couldn't figure out what to put in the accumulator. I didn't realize it didn't make a difference (unit will do) as long as it is evaluated when the Map is. Seq wrecks my head ;) Thanks! Edsko
participants (2)
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Edsko de Vries -
Felipe Lessa