问haskell的Minimax

EN

minimax:: RT Board ->Int
minimax (Tree board subtrees) = case subtrees of 
    []                                                                  >evaluate board (get_turn board)  
    _                                                                  ->case get_turn board of 
            Player_X                                                   ->maximum (next_socres)  
            Player_O                                                   ->minimum  (next_socres) 
 where next_socres = map evaluate (map get_board subtrees) 

--get the node from sub trees
get_board:: RT Board -> Board
get_board (Tree board subtrees) = board

--evaluate moves(not finished)
evaluate :: Board -> Player -> Int
evaluate board me'   
    |[me,me,me,Blank] `isInfixOf_e` all_stone_lines                         = 10
    |[opp,opp,opp,Blank] `isInfixOf_e` all_stone_lines                      = -10
    |otherwise                                                              = 0 
    where
        me = get_stone_of me'
        opp = opponent' me
        all_stone_lines = combine_list stones_from_rows (combine_list     stones_from_cols (combine_list stones_from_left_dias                  stones_from_right_dias))   
        stones_from_rows = map (get_from_row board) [1..board_size] 
        stones_from_cols = map (get_from_column board) [1..board_size] 
        stones_from_left_dias = map (get_from_left_diagonal board) [-(board_size-1)..(board_size-1)]
        stones_from_right_dias = map (get_from_right_diagonal board) [2..(2*board_size)]