import Control.Monad
import Data.Monoid

dotest x = do
    if x then return "Test"
         else return "OK" 

type KnightPos = (Int, Int)

moveKnight :: KnightPos -> [KnightPos]
moveKnight (c, r) = do
    (c', r') <- [(c+2,r-1),(c+2,r+1),(c-2,r-1),(c-2,r+1)
            ,(c+1,r-2),(c+1,r+2),(c-1,r-2),(c-1,r+2)]
    guard (c' `elem` [1..8] && r' `elem` [1..8])
    return (c', r')

filterDup :: [KnightPos] -> [KnightPos]
filterDup [] = []
filterDup (x:xr) = x:(filterDup $ filter (x/=) xr)

singleStep x = filterDup $ x >>= moveKnight

multiStep :: Int -> [KnightPos] -> [KnightPos]
multiStep 0 x = x
multiStep n x = multiStep (n-1) (singleStep x)

applyLog :: (Monoid m) => (a, m) -> (a -> (b, m)) -> (b, m)
applyLog (x, log) f = let (y, newLog) = f x in (y, log `mappend` newLog)