fu funkcija

FUnkcija.hs

validateMoveOrder :: [Move] -> Maybe String
validateMoveOrder [] = Nothing
validateMoveOrder [_] = Nothing
validateMoveOrder l = validateCurrentMove 0 [] l turns
  where
    contains :: Eq a => [a] -> a -> Bool
    contains [] _ = False
    contains (x:xs) el = (x == el) || contains xs el
    showSquareTakenMsg :: Int -> String
    showSquareTakenMsg x =
        "Move #" ++ show (x + 1) ++ " is invalid - the square is already taken!"
    showWrongNameMsg :: Int -> String -> String -> String
    showWrongNameMsg x exp act =
        "Wrong player name on move #" ++
        show (x + 1) ++ ". Expected '" ++ exp ++ "', got '" ++ act ++ "'."
    showWrongPieceMsg :: Int -> Piece -> Piece -> String
    showWrongPieceMsg x exp act =
        "Wrong piece on move #" ++
        show (x + 1) ++
        ". Expected '" ++ show exp ++ "', got '" ++ show act ++ "'."
    xName :: String
    oName :: String
    (xName, oName) = extractPlayerNames l
    turns :: [(String, Piece)]
    turns = (xName, X) : (oName, O) : turns
    validateCurrentMove ::
           Int -> [(Int, Int)] -> [Move] -> [(String, Piece)] -> Maybe String
    validateCurrentMove _ _ [] _ = Nothing
    validateCurrentMove currMove c (x:xs) ((expName, expPiece):ts)
        | contains c (coords x) = Just (showSquareTakenMsg currMove)
        | otherwise =
            if expName ~== player x
                then if expPiece == piece x
                         then validateCurrentMove
                                  (currMove + 1)
                                  (coords x : c)
                                  xs
                                  ts
                         else Just
                                  (showWrongPieceMsg currMove expPiece (piece x))
                else Just (showWrongNameMsg currMove expName (player x))