すごいHaskell読書会 in 大阪 2周目 #16

fu.hs

type Pos = (Int, Int)
checkCol :: Pos -> [Pos] -> Bool
checkCol (row, col) l = not . elem True $ map (\(_, col') -> col' == col) l

putFu ::  Pos -> [Pos] -> Maybe [Pos]                       
putFu (row, col) l 
    | row < 1 = Nothing         
    | row > 8 = Nothing
    | col < 1 = Nothing
    | col > 9 = Nothing
    | checkCol (row, col) l == False = Nothing
    | otherwise = Just $ (row, col):l