Re: [Haskell-cafe] Memory Management and Lists

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 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" mailto:ch.howard@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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