[Haskell-cafe] Memory Management and Lists
Christopher Howard
ch.howard at zoho.com
Tue Jul 12 00:12:22 UTC 2016
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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