Erlang 中的模块函数
所以，这是我正在编写的模块的一部分：
request(Pid, ListOfDocuments) when is_pid(Pid), is_list(ListOfDocuments) ->
io:format("We get here~n"),
case whereis(jdw_api) of
undefined -> [no, api];
ApiPid when is_pid(ApiPid) ->
io:format("... and here~n"),
% (1) Won't work: spawn(?MODULE, loop, [Pid, ListOfDocuments])
% (2) Won't work, either: ?MODULE:loop(Pid, ListOfDocuments)
loop(Pid, ListOfDocuments) % (3) and neither does this...
end.
... 也是这样：
loop(Pid, Docs) when is_list(Docs), length(Docs) > 0 ->
H = hd(Docs),
T = tl(Docs),
io:format("... but not here...~w~n", H),
case ?MODE of
sync ->
Ref = make_ref(),
jdw_api ! {self(), Ref, doc, H},
Ans = loop_sync(Ref, [], []),
Pid ! Ans,
loop(Pid, T);
async -> {error, 'async mode not implemented yet', ?FILE, ?LINE};
_ -> {'?MODE must be either async or sync'}
end;
loop(Pid, Docs) -> io:format("Done with document list").
... 但由于某种原因，“循环”函数永远不会被调用。这三种不同的方式都无法让魔法发生……有什么指示吗？
So, this here is part of a module I'm writing:
request(Pid, ListOfDocuments) when is_pid(Pid), is_list(ListOfDocuments) ->
io:format("We get here~n"),
case whereis(jdw_api) of
undefined -> [no, api];
ApiPid when is_pid(ApiPid) ->
io:format("... and here~n"),
% (1) Won't work: spawn(?MODULE, loop, [Pid, ListOfDocuments])
% (2) Won't work, either: ?MODULE:loop(Pid, ListOfDocuments)
loop(Pid, ListOfDocuments) % (3) and neither does this...
end.
... and so is this:
loop(Pid, Docs) when is_list(Docs), length(Docs) > 0 ->
H = hd(Docs),
T = tl(Docs),
io:format("... but not here...~w~n", H),
case ?MODE of
sync ->
Ref = make_ref(),
jdw_api ! {self(), Ref, doc, H},
Ans = loop_sync(Ref, [], []),
Pid ! Ans,
loop(Pid, T);
async -> {error, 'async mode not implemented yet', ?FILE, ?LINE};
_ -> {'?MODE must be either async or sync'}
end;
loop(Pid, Docs) -> io:format("Done with document list").
... but for some reason, the "loop" function never gets called. Neither of the three different ways makes the magic happen... Any pointers?
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评论（1）
您的循环函数可能会被调用，但上面显示的代码只是该函数的一个子句，并且只有在使用 Pid 和非空文档列表调用时才会运行。另一个问题是您对 io:format("... 但不在这里...~w~n", H) 的错误调用应该是 io:format(".. .但不是在这里...~w~n", [H])。该调用可能会使循环代码崩溃。如果没有更多的源代码和
request/2的示例参数，很难说清楚。Your loop function might get called, but the code you show above is only one clause of that function, and it will only run if called with a Pid and a non-empty list of documents. The other problem is your buggy call to
io:format("... but not here...~w~n", H)which should beio:format("... but not here...~w~n", [H]). That call might be crashing the loop code. Without more source to work from and example arguments torequest/2it's hard to tell.