Hi,
I seem to be a little stuck with incremental array updates... I've got
an array of "few" (some thousand) integers, but have to do a calculation
where I incrementally build up the array. For sake of simplicity, for
now I don't use a State-Monad but simply pass the array as state down
the recursive calls.
Unfortunatelly, I seem to experience problems with lazyness; when I run
my program, memory usage goes up to horrific values! The simple program
below reproduces this; when run on my machine, it uses up about 300 MB
of real and 300 MB of virtual memory, and the system starts swapping
like mad! I compiled with ghc --make -O3, ghc version 6.8.3 if that
matters.
BTW, I tried to make the array update strict using the `seq` as below,
but with no effect... What am I doing wrong here?
Many thanks,
Daniel
import Data.Array;
arraySize = 1000
limit = 100000
type MyArray = Array Int Int
emptyArray :: MyArray
emptyArray = array (0, arraySize - 1) [ (i, 0) | i <- [0 .. arraySize - 1] ]
procOne :: Int -> MyArray -> MyArray
procOne a cnt
| a > limit = cnt
| otherwise =
let ind = a `mod` arraySize
oldcnt = cnt ! ind
newarr = cnt // [(ind, oldcnt + 1)]
in
procOne (a + 1) (newarr `seq` newarr)
main :: IO ()
main =
do
arr <- return $ procOne 0 emptyArray
print $ arr ! 42
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