[Haskell-cafe] Memory Management and Lists

[Christopher Howard]

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))
> 
> 

-- 
http://qlfiles.net
To protect my privacy, please use PGP encryption. It's free and easy
to use! My public key ID is 0x340EA95A (pgp.mit.edu).