Erlang中的匹配模式总结

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Erlang中的匹配模式总结

来源:互联网 作者:脚本宝典 时间:2015-07-24 13:11 【

一、赋值时匹配 原子匹配 复制代码 代码如下: atom = atom % atom another = another % another atom = another % exception error 变量匹配 复制代码 代码如下: Var = 2. % 2 Var = 3 - 1. % 2 Var = 1. % exception error 元

一、赋值时匹配

原子匹配

复制代码代码如下:


atom    = atom                        % atom
another = another                     % another
atom    = another                     % exception error


变量匹配

复制代码代码如下:


Var = 2.                              % 2
Var = 3 - 1.                          % 2
Var = 1.                              % exception error


元组匹配

复制代码代码如下:


Attr = {name, sloger}.                % {name, sloger}
{name, Name} = Attr.                  % {name, sloger}
Name.                                 % sloger


列表匹配

复制代码代码如下:


Langs = [perl, python, ruby, erlang].
[Head | Tail] = Langs.
Head.                                 % perl
Tail.                                 % [python, ruby, erlang]


参数匹配

复制代码代码如下:


sum([]) -> 0;
sum([H|T]) -> H + sum(T).


sum([1, 2, 3]).                       % 6


记录匹配

复制代码代码如下:


%% record(post, {title, slug, body, author}).


Post = #post{title = "Pattern Match in Erlang",
             slug = "pattern-match-in-erlang",
             body = "Bla bla bla...",
             author = sloger}.

#post{title = Title, slug = Slug} = Post.

Title.                                % "Erlang 中的模式匹配总结"
Slug.                                 % "summary-of-pattern-match-in-erlang"


比特匹配

复制代码代码如下:


Red = 5.
Green = 23.
Blue = 200.


Color = <<Red:5, Green:6, Blue:5>>.

<<R1:5, G1:6, B1:5>> = Color.

R1.                                   % 5
G1.                                   % 23
B1.                                   % 200


二、流程控制中的匹配


if

复制代码代码如下:



if
    Pattern1 [when Guard1] -> Expression1;
    Pattern2 [when Guard2] -> Expression2;
    %% and so on ...
    _                      -> Expression3           % 匹配所有其它结果
end.



case



复制代码代码如下:


case Expression of
    Pattern1 [when Guard1] -> Expression1;
    Pattern2 [when Guard2] -> Expression2;
    %% and so on ...
    _                      -> Expression3
end.



try catch



复制代码代码如下:


try FunctionOrExpressions of
    Pattern1 [when Guard1] -> Expression1;
    Pattern2 [when Guard2] -> Expression2
    %% and so on ...
catch
    ExType:ExPattern1 [when ExGuard1] ->
        ExExpression1;
    ExType:ExPattern2 [when ExGuard2] ->
        ExExpression2;
    %% and so on ...
    _:_ -> DefaultExExpression               % _:_ 匹配所有异常
after
    AfterExpressions
end


消息传递匹配

复制代码代码如下:


loop() ->
    receive
        {From, {rectangle, Width, Height}} ->
            From ! {self(), Width * Height},
            loop();
        {From, {circle, R}} ->
            From ! {self(), 3.14 * R * R},
            loop();
        {From, _Other} ->
            From ! {self(), {error, unknown_shape}}
            loop()
    end.
Pid = spawn(fun loop/0).
Pid ! {self(), {rectangle, 10, 5}}.         % {Pid, 50}
Pid ! {self(), {circle, 4}}.                % {Pid, 50.24}
Pid ! {self(), {square, 10}}.               % {Pid, {error, unknown_shape}}


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