Hi Ian, In case you were looking for an example to get your teeth into you might be interested in these: https://gist.github.com/2876666 These two scripts both serve the same purpose of building a map of word counts from a text file. They both use Data.Text for Unicode IO, but each tests a different structure. Though unordered-containers package with its Data.HashMap is often suggested as an efficient mapping structure, in my case (of these two scripts) the Data.HashTable from standard library wins taking circa half the time to run on the same dataset (though it's not purely functional as its actions operate in the IO monad). Finally, what puzzles me the most, is that a roughly equivalent script in Python which just reads the same datafile into a standard dict performs in about 1/3 of the time of the faster one of the above two and Python's hardly a fast language... Bewildering, indeed. Hope I didn't put you off :)