In fact it turned out that the example code I posted did not exhibit the memory leak at all. It just took a /very long time/ to complete (compared to a Java version), but it did complete. My complete code, which also counted the instances of a given number from the array, does however exhibit the leak. It is here:
quick guess, and useful pattern-to-avoid: tail-recursive functions with non-strict accumulators may be tail recursive, but they build up unevaluated expressions representing the accumulations; when those are forced by inspection, the evaluator descends non-tail-recursively into those possibly deep accumulations (..(0+1)..+1), possibly resulting in stack overflows. the worker in genSeries inspects its parameters at each call, keeping them evaluated; the worker in countNumbers inspects only its first two parameters, possibly (depending on optimizations) leaving acc unevaluated. try: worker lo (i-1) $! acc hth, claus
module Main where
import Data.Array.IO import System.Random
type Buffer = IOUArray Int Int
-- | Triangular Probability Density Function, equivalent to a roll of two dice. -- The number sums have different probabilities of surfacing. tpdf :: (Int, Int) -> IO Int tpdf (low, high) = do first <- getStdRandom (randomR (low, high)) second <- getStdRandom (randomR (low, high)) return ((first + second) `div` 2)
-- | Fills an array with dither generated by the specified function. genSeries :: Buffer -> ((Int, Int) -> IO Int) -> (Int, Int) -> IO () genSeries buf denfun lims = let worker low i | i >= low = do r <- denfun lims writeArray buf i r worker low (i - 1) | otherwise = return () in do (lo, hi) <- getBounds buf worker lo hi
countNumbers :: Buffer -> Int -> IO Int countNumbers buf x = let worker lo i acc | i >= lo = do n <- readArray buf i if n == x then worker lo (i - 1) (acc + 1) else worker lo (i - 1) acc | otherwise = return acc in do (lo, hi) <- getBounds buf worker lo hi 0
main = do buf <- newArray_ (0, 10000000) :: IO Buffer genSeries buf tpdf (2, 12) sevens <- countNumbers buf 7 putStrLn ("Magic number sevens: " ++ show sevens) return 0
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