# Haskell Quiz/Chess960/Solution Sjanssen

### From HaskellWiki

import Data.List import System.Random import System bishopRule xs = even i /= even j where [i, j] = elemIndices 'B' xs kingRule xs = i < k && k < j where [i, j] = elemIndices 'R' xs [k] = elemIndices 'K' xs white = uniq . filter kingRule . filter bishopRule . permutations $ pieces where pieces = "KQRRNNBB" printArrangement x = do putStrLn x putStrLn . reverse $ x main = do args <- getArgs case args of ["all"] -> mapM_ printArrangement white [] -> randomRIO (0, 959) >>= printArrangement . (white!!) -- Utility functions: uniq :: Ord a => [a] -> [a] uniq = map head . group . sort allInsertions x [] = [[x]] allInsertions x (y:ys) = [x:y:ys] ++ map (y:) (allInsertions x ys) permutations [] = [[]] permutations (x:xs) = concatMap (allInsertions x) . permutations $ xs