[Haskell-cafe] Why does this program eat RAM?

[Lennart Augustsson]

The x+1 looks suspicious.

On Sep 4, 2006, at 23:03 , John Goerzen wrote:

> I have the below program, and I'm trying to run it on an input of  
> about
> 90MB.  It eats RAM like crazy, and I can't figure out why.
>
> I do know that the problem is not my custwords function (as you can  
> see,
> I replaced the call to it with a call to the standard words  
> function on
> the last line).  It seems to be wordfreq, but I don't know why.
>
> For information about the problem, see
> http://changelog.complete.org/posts/535-A-Haskell-solution-to-Lars- 
> Problem.html
>
> Here's the code:
>
> import System.Environment
> import Data.List
> import Data.Char
> import qualified Data.Map as Map
>
> custwords = filter (/= "") . lines . map (conv . toLower)
>     where iswordchar x = isAlphaNum x && isAscii x
>           conv x = if iswordchar x then x else '\n'
>
> wordfreq inp = Map.toList $ foldl' updatemap (Map.empty::Map.Map  
> String Int) inp
>     where updatemap nm word = Map.insertWith updatefunc word 1 nm
>           updatefunc _ x = x + 1
>
> freqsort (w1, c1) (w2, c2) = if c1 == c2
>                                  then compare w1 w2
>                                  else compare c2 c1
>
> showit (word, count) = show count ++ " " ++ word
> main = do args <- getArgs
>           interact $ unlines . map showit . take (read . head $  
> args) .
>                      sortBy freqsort . wordfreq . words
>
>
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