[Haskell-cafe] Derving NFData via Generics from a type that has a vector doesn't work. (was trying to understand out of memory exceptions)

[Anatoly Yakovenko]

-- + Roman,

-- hey Roman,

-- seems like i cant use deepseq or Generic derive of NFData on data types
containing vectors.  The following code tries to use deepseq to force
evaluation of a type containing vectors, but when the code is running it
seems to not work as expected (blows up in memory).  any ideas?


{-# LANGUAGE DeriveGeneric #-}
import Control.DeepSeq
import System.IO
import GHC.Generics (Generic)
import qualified Data.Vector as V
import qualified Data.ByteString.Lazy.Char8 as BL

scanl' :: NFData a => (a -> b -> a) -> a -> [b] -> [a]
scanl' f q ls =  q : (case ls of
                        []   -> []
                        x:xs -> let q' = f q x
                                in q' `deepseq` scanl' f q' xs)

-- this runs without blowing up
-- main = print $ last $ scanl' (+) (0::Int) [0..]

data Simple = Simple (V.Vector Double)
            deriving (Show, Generic)

instance NFData Simple

--this blows up
main = do
   let initial = Simple $ V.fromList (take 100 $ repeat 0)
       sumvs (Simple a) (Simple b) = Simple $ V.zipWith (+) a b
   print $ last $ scanl' sumvs initial $ repeat $ initial




On Tue, Apr 16, 2013 at 12:36 PM, anatoly yakovenko
<aeyakovenko at gmail.com>wrote:

> This compiles but the process runs out of memory, so it seams that NFData
> derivation isn't doing its job.
>
>
> On Apr 16, 2013, at 12:15 PM, José Pedro Magalhães <jpm at cs.uu.nl> wrote:
>
> > What is the error that you get?
> >
> >
> > Cheers,
> > Pedro
> >
> > On Tue, Apr 16, 2013 at 8:07 PM, Anatoly Yakovenko <
> aeyakovenko at gmail.com> wrote:
> > -- ok, something in deriving NFData using Generics in a type that has a
> Vector in it.
> >
> >
> > {-# LANGUAGE DeriveGeneric #-}
> > import Control.DeepSeq
> > import System.IO
> > import GHC.Generics (Generic)
> > import qualified Data.Vector as V
> > import qualified Data.ByteString.Lazy.Char8 as BL
> >
> > scanl' :: NFData a => (a -> b -> a) -> a -> [b] -> [a]
> > scanl' f q ls =  q : (case ls of
> >                         []   -> []
> >                         x:xs -> let q' = f q x
> >                                 in q' `deepseq` scanl' f q' xs)
> >
> > -- this runs without blowing up
> > -- main = print $ last $ scanl' (+) (0::Int) [0..]
> >
> > data Simple = Simple (V.Vector Double)
> >             deriving (Show, Generic)
> >
> > instance NFData Simple
> >
> > --this blows up
> > main = do
> >    let initial = Simple $ V.fromList (take 100 $ repeat 0)
> >        sumvs (Simple a) (Simple b) = Simple $ V.zipWith (+) a b
> >    print $ last $ scanl' sumvs initial $ repeat $ initial
> >
> >
> >
> > _______________________________________________
> > Haskell-Cafe mailing list
> > Haskell-Cafe at haskell.org
> > http://www.haskell.org/mailman/listinfo/haskell-cafe
> >
> >
>
>
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