[Haskell-cafe] Memory Management and Lists

Jake jake.waksbaum at gmail.com
Mon Jul 11 22:08:03 UTC 2016


Just out of curiosity, what is the advantage to using a newtype in this
case when you will not be writing your own instances of typeclasses?

On Mon, Jul 11, 2016, 15:56 David Feuer <david.feuer at gmail.com> 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> 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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