Haskell Quiz/Chess960/Solution Sjanssen

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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