On Wednesday 04 May 2011 15:13:07, Barbara Shirtcliff wrote:
Hi,
In the following solution to problem 24, why is nub ignored?
It isn't: *LexOrder> lexOrder "00" ["0","0"] *LexOrder> lexOrder "001" ["01","10","*** Exception: Prelude.(!!): index too large
lexI :: Char -> String -> Int lexI c s = maybe 1 (id) $ elemIndex c s
lexOrder :: [Char] -> [[Char]] lexOrder s
| length s == 1 = [s] | length s == 2 = z : [reverse z] | otherwise = concat $ map (\n -> h n) [0..((length s) - 1)]
where z = sort $ nub s -- why is the nub ignored here? h :: Int -> [String] h n = map (z!!n :) $ lexOrder $ filter (\c -> lexI c z /= n) z
Your problem is (well, the one I see immediately) that you check for the length of s, where you should check for the length of z.