http://www.meetup.com/hoodlums/messages/boards/thread/17789342

NovemberHomework.hs

import Data.Enumerator hiding (map, length, foldl)
import qualified Data.Enumerator.Text as ET
import qualified Data.Enumerator.List as EL
import Data.List (sort)
import qualified Data.Map as M
import Data.Text (Text)


data Entry = Entry { date :: String
                   , host :: String
                   , program :: String 
                   , message :: String
                   } deriving Show

processFile :: IO ()
processFile = run_ syslogIteratee >>= print

-- iteratees et al.

syslogIteratee :: Iteratee Entry IO ([(Int, String)], Int)
syslogIteratee = entryEnumerator $$ entryIteratee

entryEnumerator :: Enumerator Entry IO b
entryEnumerator = syslogEnumerator $= entryParser

syslogEnumerator :: Enumerator Text IO b
syslogEnumerator = ET.enumFile "syslog"

entryIteratee :: Monad m => Iteratee Entry m ([(Int, String)], Int)
entryIteratee = EL.zipWith top10AndId summariser counter

entryParser :: Monad m => Enumeratee Text Entry m b
entryParser = EL.map parseEntry

summariser :: Monad m => Iteratee Entry m (M.Map String Int)
summariser = EL.fold updateSummary M.empty
  where updateSummary summary entry = M.insertWith' (+) (program entry) 1 summary

counter :: Monad m => Iteratee a m Int
counter = EL.fold (\acc _ -> acc + 1) 0

-- auxiliary functions

parseEntry :: Text -> Entry
parseEntry text = Entry d h p m
  where d1:d2:d3:h:p':ms = words $ show text
        d = unwords [d1,d2,d3]
        p = init p'
        m = unwords ms

top10AndId :: Ord a => M.Map a Int -> b -> ([(Int, a)], b)
top10AndId m b = (top10 m, b)

top10 :: Ord a => M.Map a Int -> [(Int, a)]
top10 = take 10 . reverse . sort . map swap . M.toList 

swap :: (a, b) -> (b, a)
swap (x, y) = (y, x)