I've added some code of mine for principal variation search in haskell to the wiki http://www.haskell.org/haskellwiki/PrincipalVariationSearch It might need a couple of strictness annotations for best performance, but it worked ok for me as is, when compiled with -O2 on GHC. It is fairly basic (lacks support for hash tables for example). But most other things can be done by generating the move tree lazily in the right way (example move ordering). Rene.