[Haskell-cafe] Streaming bytes and performance

[Branimir Maksimovic]

> To: haskell-cafe at haskell.org
> From: to.darkangel at gmail.com
> Date: Tue, 19 Mar 2013 23:27:09 +0200
> Subject: Re: [Haskell-cafe] Streaming bytes and performance
> 
> On 03/19/2013 10:49 PM, Konstantin Litvinenko wrote:
> > {-# LANGUAGE BangPatterns #-}
> >
> > import Control.Monad.State.Strict
> >
> > data S6 = S6 !Int !Int
> >
> > main_6 = do
> >      let r = evalState go (S6 10000 0)
> >      print r
> >    where
> >      go = do
> >          (S6 i a) <- get
> >          if (i == 0) then return a else (put (S6 (i - 1) (a + i))) >> go
> >
> > main_7 = do
> >      let r = go (S6 10000 0)
> >      print r
> >    where
> >      go (S6 i a)
> >          | i == 0 = a
> >          | otherwise = go $ S6 (i - 1) (a + i)
> >
> > main = main_6
> >
> > main_6 doing constant allocations while main_7 run in constant space.
> > Can you suggest something that improve situation? I don't want to
> > manually unfold all my code that I want to be fast :(.
Your problem is that main_6 thunks 'i' and 'a' .If you write (S6 !i !a) <- getthan there is no problem any more...
> 
> Correction - they both run in constant space, that's not a problem. The 
> problem is main_6 doing constant allocation/destroying and main_7 doesn't.
No main_6 does not runs in constant space if you dont use bang patterns...

 		 	   		  
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.haskell.org/pipermail/haskell-cafe/attachments/20130319/02817ce6/attachment.htm>