我的 gen_server 实现有什么问题？

Question

按照LYSE 这本书，我尝试用gen_server 重新实现kitty_server2。但由于某种原因，我收到了这个错误：

37> Cat1 = kitty_server3:order_cat(Pid, carl, brown, 2).
Ordeirng cat!** exception exit: {{function_clause,
                        [{gen,do_for_proc,
                             [{ok,<0.162.0>},#Fun<gen.0.132519590>],
                             [{file,"gen.erl"},{line,252}]},
                         {gen_server,call,2,[{file,"gen_server.erl"},{line,200}]},
                         {erl_eval,do_apply,6,[{file,"erl_eval.erl"},{line,673}]},
                         {erl_eval,expr,5,[{file,"erl_eval.erl"},{line,438}]},
                         {shell,exprs,7,[{file,"shell.erl"},{line,686}]},
                         {shell,eval_exprs,7,[{file,"shell.erl"},{line,641}]},
                         {shell,eval_loop,3,[{file,"shell.erl"},{line,626}]}]},
                    {gen_server,call,[{ok,<0.162.0>},{order,carl,brown,2}]}}
     in function  gen_server:call/2 (gen_server.erl, line 204)

我似乎已经实现了所有必需的回调，但我无法真正说出错误的含义。是说我错过了回调吗？因为它似乎甚至没有调用相关的handle_call?

这是完整的服务器实现：

-module(kitty_server3).
-behaviour(gen_server).
-export([order_cat/4, return_cat/2, close_shop/1, sell_cat/3, start/0, start_link/0]).
-export([init/1, handle_call/3, handle_cast/2, code_change/3, 
    handle_info/2, terminate/2]).

-record(cat, {name, color=green, price}).

start() -> gen_server:start(?MODULE, {[], 0}, []).
start_link() -> gen_server:start_link(?MODULE, {[], 0}, []).

%%% Client api
%% Asynchronous
return_cat(Pid, Cat = #cat{}) -> gen_server:cast(Pid, {return, Cat}).

%% Synchronous call
order_cat(Pid, Name, Color, Price) ->
    io:format("Ordeirng cat!"),
    gen_server:call(Pid, {order, Name, Color, Price}).

sell_cat(Pid, Cat, Price) ->
    gen_server:call(Pid, {sell, Cat, Price}).

close_shop(Pid) -> gen_server:stop(Pid).

%%% Callback functions
init(State) -> {ok, State}.

%%% Server functions
%% Synchronous callbacks
handle_call({order, Name, Color, Price}, _From, {Cats, Money}) ->
    io:format("Handling cat order.."),
    if Cats =:= [] ->
        io:format("1.."),
        {reply, make_cat(Name, Color, Price), {Cats, Money + Price}};
       Cats =/= [] -> % empty the stock
        io:format("2.."),
        {reply, hd(Cats), {tl(Cats), Money + Price}}
    end;

handle_call({sell, Cat, Price}, _From, {Cats, Money}) ->
    if Money >= Price ->
        {reply, Price, {[Cat|Cats], Money - Price}}; % pay the customer!
       Money < Price ->
        {reply, 0, {Cats, Money}} % pay nothing we are poor!
    end.

%% Asynchronous callbacks
handle_cast({return, Cat = #cat{}}, {Cats, Money}) ->
    {noreply, {[Cat|Cats], Money}}.

%% Terminate callback
terminate(_Reason, {Cats, Money}) ->
    release_the_cats(Cats, Money).

%% Code change callback
code_change(_OldVsn, State, _Extra) ->
    {ok, State}.

%% Handle unexpected messages callback
handle_info(Info, State) ->
    io:format("Unexpected message: ~w", [Info]),
    {noreply, State}.

%%% Private functions
make_cat(Name, Col, Price) ->
    #cat{name=Name, color=Col, price=Price}.

release_the_cats(Cats, Money) ->
    io:format("Made $~w~n", [Money]),
    [io:format("~p was set free.~n",[C#cat.name]) || C <- Cats].

有什么建议吗？

Answer 1

这对我来说很好用：

Eshell V7.2.1  (abort with ^G)
1> l(kitty_server3).
{module,kitty_server3}
2> {ok, Pid} = kitty_server3:start().
{ok,<0.36.0>}
3> kitty_server3:order_cat(Pid, carl, brown, 2).
Ordeirng cat!Handling cat order..1..{cat,carl,brown,2}
4>

也许您做了一些更改并且没有正确重新加载模块，或者您的 Erlang shell 有一些旧的变量绑定？