If you can demonstrate the required laziness/strictness properties
are identical, looks like a nice idea.
gracjanpolak:
>
> Hi all,
>
> On the other day I noticed that we could optimize 'sequence' more.
> I needed it for my monadic parser. Below is my small experiment.
> Sequence from standard library needs 2.3s to finish (and additional
> stack space), my version uses only 0.65s and default stack.
>
> Is my version better or am I missing something obvious?
>
> -- standard
> sequence1 :: Monad m => [m a] -> m [a]
> sequence1 ms = foldr k (return []) ms
> where
> k m m' = do { x <- m; xs <- m'; return (x:xs) }
>
> -- accumulator version
> sequence2 :: Monad m => [m a] -> m [a]
> sequence2 ms = sequence' [] ms
> where
> sequence' vs [] = return (reverse vs)
> sequence' vs (m:ms) = m >>= (\v -> sequence' (v:vs) ms)
>
> main = do
> let l = map return [1..1000000]
> w <- sequence1 l
> print (sum w)
> return ()
>
> [EMAIL PROTECTED]:~/some_faster> time ./Some1 +RTS -K100M
> 500000500000
>
> real 0m2.318s
> user 0m2.284s
> sys 0m0.032s
>
>
> [EMAIL PROTECTED]:~/some_faster> time ./Some2
> 500000500000
>
> real 0m0.652s
> user 0m0.592s
> sys 0m0.052s
>
> --
> Gracjan
>
>
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