Erlang 杂记 IV

休假回来,调整一下状态,先把Evernote里面一些比较零散的东西整理出来;过去一个月对于Erlang开发者还是有些惊喜的,比如《Erlang/OTP并发编程实战》终于出版了;比如<Building.Web.Applications.with.Erlang>也可以看到英文版了.下面第一条消息就是关于Erlang的另外一本好书:《Learn You Some Erlang》

 

Learn You Some Erlang 两则

  Erlang学习有一个非常棒的网站: http://learnyousomeerlang.com/

  现在有两则关于它的消息:

   [1] 首先是这本书的Kindle版本, 能够在移动设备上阅读这本书,真的是非常方便;其实不仅仅是Kindle 其它支持mobi格式的都可以完美显示;甚至你可以使用源文件自己编译成为其它格式,比如epub;

    github地址:https://github.com/igstan/learn-you-some-erlang-kindle

  [2] 这个网站的出版物已经发行,其中文版由 @淘宝褚霸 翻译,可以预见到这又将成为中文资料的经典之作

   http://book.douban.com/subject/10822017/

 

 

string To Erlang Term 一个更为考虑更为完善的方法

下面是可以解决的:

1> E=fun(S) ->{ok,Scanned,_} = erl_scan:string(S),
{ok,Parsed} = erl_parse:parse_exprs(Scanned),
erl_eval:exprs(Parsed,[]) end.
#Fun<erl_eval.6.111823515>
2> E("{quit,tom}\n"++".").
{value,{quit,tom},[]}
3>

如果是Pid的情况下会存在异常

** exception error: no match of right hand side value

                    {error,{1,erl_parse,["syntax error before: ","'<'"]}} 

然后我在这里发现了一个更为完善的做法

https://github.com/erlang/otp/blob/master/lib/tv/src/tv_db_search.erl

string_to_term(Str) ->
    case catch erl_scan:string(Str ++ ". ") of
     {ok, ScannedStr, _No} ->
         case erl_parse:parse_term(ScannedStr) of
          {ok, Term} ->
              {ok, Term};
          _Other ->
                 %% May be a PID, have to check this, since erl_scan
                 %% currently cannot handle this case...  :-(
              case catch list_to_pid(Str) of
               Pid when is_pid(Pid) ->
                   {ok, Pid};
               _Error ->
                   case get(error_msg_mode) of
                    normal ->
                        {error, {not_a_term, "Please enter a valid term!"}};
                    haiku ->
                        {error, {not_a_term, ["Aborted effort.",
                                     "Reflect, repent and retype:",
                                     "Enter valid term."]}}
                   end
              end
         end;
     _Error ->
         case get(error_msg_mode) of
          normal ->
              {error, {not_a_term, "Please enter a valid term!"}};
          haiku ->
              {error, {not_a_term, ["Aborted effort.",
                           "Reflect, repent and retype:",
                           "Enter valid term."]}}
         end
    end. 

 

binary 替换一例 注意转义符的使用

这个没有什么特别的,只是要注意转义字符的使用

85> binary:replace(<<"c:\\windows\\abc\\c.txt">>,<<92>>,<<"//">>,[global]).
<<"c://windows//abc//c.txt">>
86> binary:replace(<<"c:\\windows\\abc\\c.txt">>,<<"\\">>,<<"//">>,[global]).
<<"c://windows//abc//c.txt">>
87> 

 

ETS表中,根据表名获取ets表id,可用但是繁琐一点

 

12> Fun3=fun(Name)->[ ID|| ID <-ets:all(),Name==ets:info(ID,name)] end.

#Fun<erl_eval.6.111823515>

13> Fun3(inet_db).

[inet_db]

14> Fun3(code).

"\r"

15> Fun3(code_names).

[4110]

16>

 

erlang模块下面有一个非常好用的解包方法

下面的解析可以使用string或binary模块自行解析,其实使用erlang:packet直接可以得到结果

Eshell V5.9.1  (abort with ^G)
1> erlang:decode_packet(http,<<"GET http://www.google.com HTTP/1.1\n">>,[]).
{ok,{http_request,'GET',
                  {absoluteURI,http,"www.google.com",undefined,"/"},
                  {1,1}},
    <<>>}
2> erlang:decode_packet(1,<<3,"abcd">>,[]).
{ok,<<"abc">>,<<"d">>}
3>  erlang:decode_packet(1,<<5,"abcd">>,[]).
{more,6}
4>

 

erlang:decode_packet的官方文档地址:http://www.erlang.org/doc/man/erlang.html

 

Erlang字符串处理的两个开源项目

[1] http://code.google.com/p/starling/

Unicode strings for Erlang

Starling is a Unicode string library for Erlang based on ICU, the best implementation of Unicode.

It's implemented as a C pipe driver packaged as an OTP application. Strings are stored as binaries internally. Compatibility layer with the standard string module is provided.

A mailing list has been set up at http://groups.google.com/group/starling-discuss.

The project homepage is at http://12monkeys.co.uk/starling.

[2]https://github.com/beerriot/icu4e icu4e: Erlang NIF wrappers around icu4c

 

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分类: Erlang