Hi again. In http://book.realworldhaskell.org/read/concurrent-and-multicore-programming.h... there is a map reduce based log parser. I have written an alternative version: http://paste.pocoo.org/show/85699/ but, with a file of 315 MB, I have [1]: 1) map reduce implementation, non parallel real 0m6.643s user 0m6.252s sys 0m0.212s 2) map reduce implementation, parallel with 2 cores real 0m3.840s user 0m6.384s sys 0m0.652s 3) my implementation real 0m8.121s user 0m7.804s sys 0m0.216s What is the reason of the map reduce implementation being faster, even if not parallelized? It is possible to implement a map reduce version that can handle gzipped log files? [1] These tests does not consider the "first run". For the first run (no data in OS cache), I have (not verified): 1) map reduce implementation, parallel with 2 cores real 0m3.735s user 0m6.328s sys 0m0.604s 2) my implementation real 0m13.659s user 0m7.712s sys 0m0.360s Thanks Manlio Perillo