Question

This code seems a bit obtuse to me… Anyone care to help me out by explaining it?

uniq_c l = [ nl (tam l) i s | (s,i) <- uniq_c' l]

tam = maximum . map snd . uniq_c'

uniq_c' [] = []
uniq_c' (h:t) = let (list,rest) = span (==h) t
                    n = length list + 1
                in (h,n) : uniq_c' rest

nl tam n line = let l = length $ show n
                    l_tam = length $ show tam
                    n' = replicate (l_tam-l) " "
                in concat n' ++ show n ++ " " ++ line

Answer 1

uniq_c provides a count of the number of times a string occurs in a list of strings concatenated with a space to the particular string:

*A> uniq_c ["The","quick","brown","fox","fox"]
["1 The","1 quick","1 brown","2 fox"]

*A> uniq_c $ ["The","quick","brown","fox","fox","fox"] ++ (replicate 100 "fox")
["  1 The","  1 quick","  1 brown","103 fox"]

uniq_c' provides a list of tuples of (string,count).

tam finds the largest count (which will be the last occurrence for any particular string).

nl indents the counts so that the counts are right justified.

*A> mapM_ putStrLn $ uniq_c $ ["The","quick","brown","fox","fox","fox"] ++ (replicate 100 "fox")
  1 The
  1 quick
  1 brown
103 fox