shintoist, I'm glad to read these. Your target audience is not just people who know haskell but have not built anything yet. Plenty of stuff can be built without using a parser, and of course that tends to evolve into code that should probably be using a parser here and there, but isn't. :) Add to that RWH documenting only parsec, and barely being published in time to show applicative use of it, and there's some need for newer examples.

I wish your types were more expressive. Using "" to cover up a failure, rather than using Maybe is somewhat of a code smell for me. Similarly, if I were parsing these logs I'd want numeric byte sizes, not strings.

Finally, I was personally thrown for a loop when you talked about using Data.Map, but threw in a Data.HashMap, apparently for performance reasons. Particularly because you continually insert values into the map, which is bad news for Data.Map (should use fromListWith when using it), but is apparently ok with HashMap, although no better than just using Data.HashMap.fromListWith.