Adrian Hey wrote:

Using explicit seqs rather than strict data types is actually faster, for reasons that are a bit of a mystery to me. I'm not sure what cost Bertram is talking about, but AFAIK ghc uses the same info pointer mechanism for all heap records, including unevaluated thunks (although the info pointers will point to different things of course). But the cost of pattern matching on *evaluated* AVL nodes should be independent of strictness annotation AFAICS.

Thanks for chiming in Adrian. Just to get started I removed the strictness annotations from the Data.Map Bin constructor, made no other changes, and ran a silly benchmark (at the end of this email). The version without bangs is actually faster than the version currently shipping. I get about 10.5 sec for the lazy version and 11.5 sec for the strict version (2.1Ghz Intel Core) I'll repeat that in bold for people just skimming this thread: __Removing Strictness Annotations Makes It Go Faster__ The reason I think is that the helper functions bin, join and balance already provide just enough strictness, as they need to inspect the size field. The strictness analyzer can then do its job. The case for IntMap is tricker, as there is no implicit strictness in the code so removing the bangs causes stack overflows. Still working on that one. Here are the benchmarks. The lazy version also evaluates "keySum dmap" slightly faster (repeated inserts) and its a tie for "keySum smap" (sequential inserts). I admit this benchmark is goofy, if you have a better one please share. Scott import qualified Data.Map as Map import Data.List as List n = 1000000 rkeys = [ (i*122789) `mod` 1006471 | i<-[0..] ] :: [Int] dkeys = map (`div`1000) rkeys :: [Int] skeys = [0..] :: [Int] shuffle (a:b:c:d:e:f:g:h:rest) = e:a:h:d:c:b:g:f: shuffle rest keySum = List.foldl' (+) 0 . Map.keys rmap = Map.fromList . take n . shuffle $ rkeys `zip` [0..] dmap = Map.fromList . take n . shuffle $ dkeys `zip` [0..] smap = Map.fromAscList . take n . shuffle $ skeys `zip` [0..] mix (x:xs) (y:ys) = x : y : mix xs ys mix _ [] = [] mix [] _ = [] rkeys2 = [ (i*122789) `mod` 1006471 | i<-[0..] ] :: [Int] rlooks = [ (i*122819) `mod` 1006471 | i<-[0..] ] :: [Int] rlook = List.foldl' (\k s -> case Map.lookup k rmap of Nothing -> s; Just x -> s+x) 0 (take n $ rkeys2 `mix` drop 1000 rlooks) main = print rlook -- or print (keySum dmap) or whatever