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Today's Topics:
1. Re: Stack overflow folding a map (Mateusz Kowalczyk)
----------------------------------------------------------------------
Message: 1
Date: Sat, 16 Feb 2013 16:46:07 +0000
From: Mateusz Kowalczyk <[email protected]>
Subject: Re: [Haskell-beginners] Stack overflow folding a map
To: [email protected]
Message-ID: <[email protected]>
Content-Type: text/plain; charset=ISO-8859-1
[1] might help you.
[1] - http://www.haskell.org/haskellwiki/Foldr_Foldl_Foldl%27
Mateusz K.
On 16/02/13 09:13, tcollin371 wrote:
> I've been playing around with Haskell on and off for a while, and am getting
> a "Stack space overflow" that I can't seem to correct. I have a map
> containing about 2 million items. Actually, it's a map keyed off of an Int
> where the element is another map keyed off of a string that has three Ints as
> its data. The number of top level maps is pretty small (< 50), and the maps
> held by them hold a lot of entries.
>
> I want to walk through all of the entries and gather some statistics, but I
> keep getting the stack overflow. I worked down my test to an inner and outer
> fold that just counts the entries, and I still get the stack overflow. I
> added 'seq' calls to make sure that the count isn't building up a bunch of
> undone operations, and I'm using foldlWithKey, and have also tried
> foldlWithKey' with the same result.
>
> I get the count in my main function and immediately print it out. Here is
> the relevant code:
>
> outputIfNotFilteredCount1 :: Int -> KeyMap -> PuzzleMapRecord -> Int
> outputIfNotFilteredCount1 inCount key entry
> = seq inCount (inCount + 1)
>
> outputDatabaseCount1 :: Int -> Int -> InnerDB -> Int
> outputDatabaseCount1 inCount smndCount innerDB
> = seq inCount (inCount + outCount)
> where
> outCount
> = Map.foldlWithKey' outputIfNotFilteredCount1 0 innerDB
>
> main = do
> ...
> let
> count = Map.foldlWithKey' outputDatabaseCount1 0 resultDB
> putStrLn $ "Database entries:" ++ (show count)
>
>
> Any thoughts on why this is running out of stack space?
>
> -Truman
>
>
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