On 1/24/13 9:31 AM, Daniel Díaz Casanueva wrote:

import Control.Monad

import qualified Data.Sequence as Seq

type Seq = Seq.Seq

f :: Monad m => Int -> m a -> m (Seq a)
f n = fmap Seq.fromList . replicateM n

g :: Monad m => Int -> m a -> m (Seq a)

g = Seq.replicateM

Maybe is just in my test case, where the Int argument is big and the monadic action short, but it looks to me that Data.Sequence.replicateM can be faster than it is right now.

Are you forcing the full sequence in both cases? In the former case, you'll get all the actions, but have a thunk containing the result of Seq.fromList. In the latter, you're performing the actions as you build the sequence, so the resultant sequence will be fully evaluated.

I imagine that this is the reason that the former seems faster to you.

--g