[Haskell-cafe] Memory Management and Lists

Christopher Howard ch.howard at zoho.com
Mon Jul 11 15:01:24 UTC 2016

-- 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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