erlang客户端程序学习（一）

area_server.erl

-module(area_server).
-export([loop/0]).
loop() ->
    receive
        {rectangle, Width, Ht} ->
            io:format("Area of rectangle is ~p~n", [Width * Ht]),
            loop();
        {circle, R} ->
            io:format("Area of circle is ~p~n", [3.14*R*R]),
            loop();
        Other ->
            io:format("I do not know what the area of a ~p is ~n", [Other]),
            loop()
    end.


测试过程：
1> c(area_server).
{ok,area_server}
2> Pid = spawn(fun area_server:loop/0).
<0.39.0>
3> Pid ! {circle, 67}.
Area of circle is 14095.46
{circle,67}

第一次改进：

-module(area_server).
-export([loop/0, rpc/2]).
rpc(Pid, Request) ->
    Pid ! {self(), Request},
    receive
        Response ->
            Response
    end.
loop() ->
    receive
        {From, {rectangle, Width, Ht}} ->
            From ! {rectangle, Width*Ht},
            loop();
        {From, {circle, R}} ->
            From ! {circle, 3.14*R*R},
            loop();
        {From, Other} ->
            Error = "Sorry, error!",
            From ! {Error,Other},
            loop()
    end.


测试：
4> c(area_server).
{ok,area_server}
6> Pid = spawn(fun area_server:loop/0).
<0.53.0>
7> area_server:rpc(Pid, sockes).      
{"Sorry, error!",sockes,ok}

改进2：

-module(area_server).
-export([loop/0, rpc/2]).
rpc(Pid, Request) ->
    Pid ! {self(), Request},
    receive
        {Pid, Response} ->
            Response
    end.
loop() ->
    receive
        {From, {rectangle, Width, Ht}} ->
            From ! {self(), Width*Ht},
            loop();
        {From, {circle, R}} ->
            From ! {self(), 3.14*R*R},
            loop();
        {From,Other} ->
            From ! {self(), error, Other},
            loop()
    end.


测试：
2> c(area_server).
{ok,area_server}
3> Pid = spawn(fun area_server:loop/0).
<0.43.0>
4> area_server:rpc(Pid, {rectangle, 8, 6}).
48
改进3：

-module(area_server).
-export([start/0]).
start() ->
    Pid = spawn(fun loop/0),
    rpc(Pid, {rectangle, 8, 6}).
rpc(Pid, Request) ->
    Pid ! {self(), Request},
    receive
        {Pid, Response} ->
            Response
    end.
loop() ->
    receive
        {From, {rectangle, Width, Ht}} ->
            From ! {self(), Width*Ht},
            loop();
        {From, {circle, R}} ->
            From ! {self(), 3.14*R*R},
            loop();
        {From,Other} ->
            From ! {self(), error, Other},
            loop()
    end.


测试：
2> c(area_server).
{ok,area_server}
3> area_server:start().
48
4> area_server:start().
48
5>