F＃2d數組索引錯誤

Question

以下代碼給出錯誤The operator 'expr.[idx]' has been used an object of indeterminate type based on information prior to this program point. Consider adding further type constraints。我想我已經告訴過它的類型。哪裏不對？

let board = Array2D.init 30 30 (fun x y -> 0) 

let tickCell x y board : int[,] = 
    match board with 
    |board when board.[x].[y] = 0-> 1 
    |board when board.[x].[y] = 1-> 0 
    | _ -> -1 

let board2 = Array2D.init 30 30 (fun x y -> tickCell x y board) 

Answer 1

這些小變化應該擺脫錯誤：

1. 包裹board參數和類型在括號中

2. 訪問與[x,y]

   let tickCell x y (board : int[,]) = 
       match board with 
       |board when board.[x,y] = 0-> 1 
       |board when board.[x,y] = 1-> 0 
       | _ -> -1