[Haskell-cafe] Memory Management and Lists

David Feuer david.feuer at gmail.com
Mon Jul 11 19:56:23 UTC 2016


Please repost your code, giving a type signature for each top-level
binding. Without them, the code is very difficult to follow. I also
strongly recommend using a newtype for your custom monad. Something like
this:

{-# LANGUAGE GeneralizedNewtypeDeriving, MultiParamTypeClasses,
StandaloneDeriving, ... #-}

newtype StateReader s c a = SR {runSR :: StateT s (Reader c) a} deriving
(Functor, Applicative, Monad)

deriving instance MonadReader c (StateReader s c)
deriving instance MonadState s (StateReader s c)
On Jul 11, 2016 11:07 AM, "Christopher Howard" <ch.howard at zoho.com> wrote:

> -- I'm a bit embarrassed of this code because I haven't yet optimized
> -- the 'stamp' algorithm for reduced number of matrix operations. But
> -- even in this state I should think the memory requirements shouldn't
> -- exceed 1MB while generating the nth Matrix, unless Matrix n-1, n-2,
> -- etc. are being preserved in memory unnecessarily.
>
> -- Monad Stack
>
> type StateReader s c a = StateT s (Reader c) a
>
> evalStateReader m s c = (runReader (evalStateT m s)) c
>
> -- Helper function
>
> type Point = (Float, Float)
> type Metric = Point -> Point -> Float
>
> euclidean :: Metric
> euclidean (x1, y1) (x2, y2) = sqrt ((x2 - x1)**2 + (y2 - y1)**2)
>
> -- monadic function. haven't had chance yet to optimize algorithm to
> -- reduce number of matrix operations
>
> stamp = do radius <- ask
>            (oMatrix, walk) <- get
>            (wX, wY) <- (return . head) walk
>            let nMatrix = matrix (nrows oMatrix) (ncols oMatrix)
>                  (\(x, y) -> let (x', y') = (fromIntegral x, fromIntegral
> y)
>                              in if euclidean (x', y') (wX, wY) > radius
>                                 then getElem x y oMatrix
>                                 else getElem x y oMatrix + 1)
>              in put (nMatrix, tail walk) >> get
>
>
>
> -- sequences and gathers results as list
>
> stampingStates initMx radius walk =
>   map fst $ evalStateReader (sequence (repeat stamp)) (initMx, walk) radius
>
>
> -- Some quick experimentation code. h is the list
>
> h = stampingStates initMx radius walk'
>   where initMx = zero 250 250
>         radius = 40
>         walk' = walk 40 (125, 125) (mkStdGen 31415)
>
> -- get 2001st Matrix and convert to Gloss Picture, employing
> -- some color interpretation code
>
> intensityG = let mx = head (drop 2000 h)
>              in toImage mx (lightnessInt 272 (minMax mx))
>
>
> On 07/10/2016 10:30 AM, Tom Ellis wrote:
> > On Sun, Jul 10, 2016 at 07:41:31AM -0800, Christopher Howard wrote:
> >> issue: a Matrix itself should only be, I'm guessing, somewhere around
> >> 100KB. But instead I'm maxing out the 3GB of RAM on my old T60 laptop.
> >> Maybe I'm generating list elements (Matrices) a lot faster than memory
> >> management is releasing them...?
> >
> > You have almost certainly got a space leak.  Can you post your code?
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