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Today's Topics:
1. Re: Stack overflow folding a map (tcollin371)
----------------------------------------------------------------------
Message: 1
Date: Sun, 17 Feb 2013 23:27:56 -0800 (GMT-08:00)
From: tcollin371 <tcollin...@earthlink.net>
Subject: Re: [Haskell-beginners] Stack overflow folding a map
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <beginners@haskell.org>
Message-ID:
<26727168.1361172476789.javamail.r...@elwamui-huard.atl.sa.earthlink.net>
Content-Type: text/plain; charset=UTF-8
It turns out that the problem isn't the counting code in the fold operations,
but instead seems to be lazy evaluation that's happening as the map is built.
If I run through the count operation every few thousand inserts, then I don't
get the stack overflow operation.
-Truman
-----Original Message-----
>From: tcollin371 <tcollin...@earthlink.net>
>Sent: Feb 16, 2013 1:13 AM
>To: Hask <beginners@haskell.org>
>Subject: [Haskell-beginners] Stack overflow folding a map
>
>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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