Elixir/Phoenix多次嘗試函數，捕捉：ok

Question

我有一個函數ping()，導致{:ok}或{:error}。

是否有可能使一個包裝功能部件test()，將嘗試ping() 5倍，返回一個錯誤之前，除非這些ping()之一，{:ok}迴應？

如果test()可以從ping()第一次嘗試返回{:ok}，那麼它應該退出遞歸，但如果沒有，則繼續嘗試ping()另外4次。

我檢查了try/catch，但似乎無法確定如何使其工作。任何提示讚賞！

Answer 1

這裏不需要try/catch。用case聲明匹配響應一個簡單的遞歸函數就足夠了：

defmodule A do 
    # A function that returns `{:ok}` a third of the times it's called. 
    def ping, do: if :random.uniform(3) == 1, do: {:ok}, else: {:error} 

    # 5 attempts. 
    def test(), do: test(5) 

    # If 1 attempt is left, just return whatever `ping` returns. 
    def test(1), do: ping() 
    # If more than one attempts are left. 
    def test(n) do 
    # Print remaining attempts for debugging. 
    IO.inspect {n} 
    # Call `ping`. 
    case ping() do 
     # Return {:ok} if it succeeded. 
     {:ok} -> {:ok} 
     # Otherwise recurse with 1 less attempt remaining. 
     {:error} -> test(n - 1) 
    end 
    end 
end 

測試：

iex(1)> A.test 
{5} 
{4} 
{3} 
{2} 
{:ok} 
iex(2)> A.test 
{5} 
{4} 
{3} 
{2} 
{:error} 
iex(3)> A.test 
{5} 
{:ok} 
iex(4)> A.test 
{5} 
{:ok} 
iex(5)> A.test 
{5} 
{4} 
{:ok}