[99p]Knight's Tour

import Data.List
import Data.Function

----- Knight's Tour Function
eightDir :: (Int, Int) -> [(Int, Int)]
eightDir r = [(x -2, y +1),(x -1, y +2),(x -2, y -1),(x -1, y -2),
              (x +2, y -1),(x +1, y -2),(x +2, y +1),(x +1, y +2)]
             where x = fst r
                   y = snd r
knighTour' :: Int -> Int -> [[(Int,Int)]] -> [[(Int,Int)]]
knighTour' n 1 routes = routes
knighTour' n size routes = knighTour' n (size-1) (concatMap stepUp routes)
                           where stepUp route = [ route ++ [s] | s <- sortedaccess (last route)]
                                                where sortedaccess r = sortBy (compare `on` accessibility) (filter ( \x -> (x `notElem` route) && (inRegion x) ) (eightDir r))
                                                      inRegion x = (fst x >= 1) && (fst x <= n) && (snd x >= 1) && (snd x <= n)
                                                      accessibility x = length $ filter ( \x -> (x `notElem` route) && (inRegion x) ) (eightDir x)
knighTour :: Int  -> [[(Int,Int)]]
knighTour n = knighTour' n (n*n) [[(1,1)]]