[Haskell-cafe] Memory Management and Lists

[Anatoly Yakovenko]

have you tried adding some strict evaluation to your algorithm?  The easy
spot to do that when using the state monad is in the state variable.




On Mon, Jul 11, 2016 at 5:12 PM Christopher Howard <ch.howard at zoho.com>
wrote:

>
>
>
> On 07/11/2016 11:56 AM, David Feuer wrote:
> > 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
> > <mailto: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)
> >
>
> stamp :: StateReader (Matrix Float, [Point])
>            Float (Matrix Float, [Point])
>
>
> >     -- 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
> :: Matrix Float -> Float -> [Point] -> [Matrix Float]
>
>
> >     stampingStates initMx radius walk =
> >       map fst $ evalStateReader (sequence (repeat stamp)) (initMx, walk)
> >     radius
> >
> >
> >     -- Some quick experimentation code. h is the list
> >
>
> h :: [Matrix Float]
>
> intensityG :: Picture
>
> displayIntensityG :: IO ()
>
> >     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))
> >
> >
>
> --
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