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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)
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