[Haskell-cafe] Optimizing spelling correction program

Don Stewart dons at galois.com
Sun Jun 21 16:18:01 EDT 2009

> Hi all,
> I want to learn how to optimize Haskell code on the Norvig's spelling
> correction program [1]. Peter Norvig has written the program in
> Python,
> quite a literate translation to Haskell (thanks to Grzegorz Chrupala)
> [2] was also available.
> Both versions are about 23 LOCs, and Haskell version is four times
> slower, 2m25s versus 36s. All the numbers I give come from running the
> program on a list of 806 misspellings, Haskell version compiled with -
> O2
> and -fforce-recomp flags.
> I started with trial and error approach. Just preventing a repetitive
> call to keysSet brought the running time down to 1m48s. I also
> restructured the edits1 function and dropped all uses of sets, which
> haven't been pulling their own weight. This brought the running time
> down to 55s. Not quite there yet but close.
> Reading the Profiling chapter in the RWH book enabled me to do some
> more
> informed optimizing. At this point the GC time was about 2% of the
> overall runnig time, Grzegorz has done a good job of using strict
> versions of functions where necessary. The timing per expression
> however
> showed something useful, 70% of the time was being spent around
> determining membership in the known words dictionary (Data.Map). There
> are about 30 000 items in the dictionary.

What are the keys in your Map? Strict ByteStrings?

And you're using ghc 6.10.x?

-- Don

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