Erlang：case..of構造函數調用返回？

Question

由代碼生成的誤差

2> X = "2". 
"2" 
3> case_:main(X). 
main 50 
sender 50 
** exception error: bad argument 
    in function case_:sender/1 (case_.erl, line 14) 
    in call from case_:main/1 (case_.erl, line 6) 
4> Z = 2. 
2 
5> case_:main(Z). 
** exception error: bad argument 
    in function io:format/3 
     called as io:format(<0.25.0>,"main ~p~n",2) 
    in call from case_:main/1 (case_.erl, line 5) 
6> 

在第一次嘗試我試圖通過這使得它有很多比更遠的第二次嘗試傳遞一個整數的字符串。我不知道爲什麼這不起作用。

函數調用sender(Input)應該從receiver()函數調用中返回{Data}。

我絕對需要程序的消息傳遞部分，因爲我試圖編寫一個需要消息的循環，對它們進行評估並返回結果;但也許case...of聲明可能被拋出。

-module(case_). 
-export([main/1, sender/1, receiver/0]). 

main(Input) -> 
    io:format("main ~p~n",Input), 
    case sender(Input) of 
     {Data} -> 
      io:format("Received ~p~n",Data) 
    end. 

sender(Input) -> 
    io:format("sender ~p~n",Input), 
    Ref = make_ref(), 
    ?MODULE ! { self(), Ref, {send_data, Input}}, 
    receive 
     {Ref, ok, Data} -> 
      {Data}  
    end.  

receiver() -> 
    io:format("receiver ~n"), 
    receive 
     {Pid, Ref, {send_data, Input}} -> 
      Pid ! { Ref, ok, Input + Input} 
    end. 

Answer 1

令人高興的是，badarg修復很容易完成。 io:format/2將術語列表作爲第二個參數。請參閱：

(Erlang R15B02 (erts-5.9.2) [source] [64-bit] [smp:8:8] [async-threads:0] [hipe] [kernel-poll:false] 

Eshell V5.9.2 (abort with ^G) 
1> io:format("main ~p~n", 2). 
** exception error: bad argument 
    in function io:format/3 
     called as io:format(<0.24.0>,"main ~p~n",2) 
2> io:format("main ~p~n", [2]). 
main 2 
ok 

你的第二個問題是，?MODULE只是返回當前模塊的名稱的原子。您需要將您的消息發送到進程。如果您修改代碼看起來像這樣：

-module(case_). 
-export([main/1, sender/2, receiver/0]). 

main(Input) -> 
    io:format("main ~p~n", [Input]), 
    Recv = spawn(?MODULE, receiver, []), 
    case sender(Recv, Input) of 
     {Data} -> 
      io:format("Received ~p~n", [Data]) 
    end. 

sender(Pid, Input) -> 
    io:format("sender ~p~n", [Input]), 
    Ref = make_ref(), 
    Pid ! { self(), Ref, {send_data, Input}}, 
    receive 
     {Ref, ok, Data} -> 
      {Data} 
    end. 

receiver() -> 
    io:format("receiver ~n"), 
    receive 
     {Pid, Ref, {send_data, Input}} -> 
      Pid ! { Ref, ok, Input + Input} 
    end. 

然後在REPL互動：

Erlang R15B02 (erts-5.9.2) [source] [64-bit] [smp:8:8] [async-threads:0] [hipe] [kernel-poll:false] 

Eshell V5.9.2 (abort with ^G) 
1> c("case_"). 
{ok,case_} 
2> case_:main(2). 
main 2 
sender 2 
receiver 
Received 4 
ok