Don Stewart wrote:
> dons:
[...]
> Just serialising straight lists of pairs,
[...]
> And reading them back in,
>
> main = do
> [f] <- getArgs
> m <- decode `fmap` L.readFile f
> print (length (m :: [(B.ByteString,Int)]))
> print "done"
Well, you don't actually read the whole list here, just its length:
instance Binary a => Binary [a] where
put l = put (length l) >> mapM_ put l
get = do n <- get :: Get Int
replicateM n get
To demonstrate, this works:
main = do
L.writeFile "v" (encode (42 :: Int))
m <- decode `fmap` L.readFile "v"
print (length (m :: [Int]))
So instead, we should try something like this:
import Control.Parallel.Strategies
instance NFData B.ByteString where
rnf bs = bs `seq` ()
main = do
[f] <- getArgs
m <- decode `fmap` L.readFile f
print (rnf m `seq` length (m :: [(B.ByteString,Int)]))
My timings:
reading list, without rnf:
0.04s
with rnf:
0.16s
reading a Data.Map:
0.52s
with rnf:
0.62s
Bertram
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