The following is a slap-dash program for generating a list of pairs of words which differ by, at most, one letter. It's quite verbose at the moment, because (a) that was the way I wrote it, a snippet at a time, and (b) I lack the wit to make it shorter. Can anyone recommend ways to make this program more efficient/neat/elegant? It runs in decent time on my machine, but it's not exceedingly pretty and I'm sure it can be made shorter too. (The full thing can be found at http://193.219.108.225/code/fingerspell/ if you want to pull in a working version to play with. The purpose of the program is for a game to practise fingerspelling when learning sign language. More on that here: http://brokenhut.livejournal.com/265471.html.) Cheers, D. ---- edited highlights below ---- -- Number of letters difference between two words. difference :: Pair -> Int difference = length . filter (==False) . uncurry (zipWith (==)) -- Keep only pairs that differ by at most -- one letter difference. keepOneDiff :: PairSet -> PairSet keepOneDiff = map snd . filter (\x -> (fst x) < 2) . map (difference &&& id) -- Pairs of words of equal length, sorted to reduce -- duplicates of (a,b), (b,a) type. They shouldn't -- be completely eradicated because part of the game -- is to spot when they;re the same word. listPairs :: WordSet -> PairSet listPairs ws = [ (w, w') | w <- ws, w' <- ws, length w == length w', w <= w' ] -- Take N pairs of words which are the same -- length and differ by at most one letter. wordpairs :: Int -> WordSet -> PairSet wordpairs n = take n . keepOneDiff . listPairs fingerspell wl p = do wordfile <- words `liftM` readFile "/usr/share/dict/words" mapM_ pretty $ wordpairs p $ filter (requirements) wordfile -- Make sure all the words are of the required length and are -- just made up of letters, not punctuation. where requirements w = length w == wl && all (isAlpha) w pretty (x,y) = putStrLn $ x ++ ", " ++ y