gistfile1.hs

import Data.ByteString.Lazy as BSL
import Data.ByteString.Lazy.Char8 as BSC
import Data.Set as Set

tlds :: Set ByteString
tlds = Set.map BSC.pack $ Set.fromList ["biz", "bz", "cc",
                                        "co", "com", "es", "info",
                                        "io", "me", "net", "org",
                                        "pro", "tv", "us", "ws"]

dropPrefix prefix word = BSC.drop (BSC.length prefix) word

coword prefix word = append (dropPrefix prefix word)
                            prefix

coWords dict word = 
    let prefixes = Set.filter (`isPrefixOf` word) tlds 
    in
    Set.filter (\pre -> (member (dropPrefix pre word) dict)
                        || (member (coword pre word) dict))
               prefixes

main = do file <- BSL.readFile "/usr/share/dict/words"
          let dict = Set.fromList $ BSC.words file
          let wordsWithCowords = Set.filter (\x -> (coWords dict x) /= Set.empty) dict
          print $ Set.map BSC.unpack wordsWithCowords