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Spelling Corrector in Haskell

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Haskell implementation (outlined in a blog post) of the simple spelling corrector by Peter Norvig, which he describes in detail in the excellent essay "How to Write a Spelling Corrector". Any credit should go to him!


git clone
cd spell
cabal sandbox init
cabal install

If you prefer using Stack, run stack install instead of that Cabal nonsense.


For taking a first look, run cabal repl or stack ghci. Some examples:

*Spell> correction "scandinaiva"
*Spell> correction "inndeed"
*Spell> correction "photograf"


  • Performance is somewhat lacking. If you manage to significantly improve performance or reduce dependencies without major structural modifications (or just add more unit tests), please don't hesitate before filing an issue or sending a pull request.
  • Haskell is lazy, so it won't parse the big.txt file until you call correction. As a result, the first correction might take a few seconds -- subsequent ones will be faster.
  • If you want, you can use this Cabal package as a dependency in your project (of course, there are better spell checkers). Since it's not on Hackage, run cabal sandbox add-source <path to local clone of spell package> in your project directory before adding spell to the build-depends list in your .cabal file.
  • In case you modify or replace big.txt: the changes may not take effect until you re-run cabal install. That's because it's listed in the data-files field of spell.cabal, enabling Cabal to provide an absolute path to big.txt at runtime, which is helpful if you want to use the spell package as a library or from any path on your system.
  • If you want to be able to run the included Hspec unit tests, replace the cabal install step above with cabal install --enable-tests. Run the tests by means of cabal test or, for incremental and more colorful output, cabal exec -- runhaskell -isrc -itest test/Spec.hs. If you're using Stack, simply run stack test.
  • Run cabal haddock or stack haddock to generate documentation.


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