扫描器erl_scan

Erlang提供的基本扫描器是erl_scan，里面提供了两个重头函数

string(String) -> Return
string(String, StartLocation) -> Return
string(String, StartLocation, Options) -> Return

Types:

String = string()
Options = options()
Return = {ok, Tokens :: tokens(), EndLocation}
       | {error, ErrorInfo :: error_info(), ErrorLocation}
StartLocation = EndLocation = ErrorLocation = location()

 

tokens(Continuation, CharSpec, StartLocation) -> Return
tokens(Continuation, CharSpec, StartLocation, Options) -> Return

Types:

Continuation = return_cont() | []
CharSpec = char_spec()
StartLocation = location()
Options = options()
Return = {done,
          Result :: tokens_result(),
          LeftOverChars :: char_spec()}
       | {more, Continuation1 :: return_cont()}
char_spec() = string() | eof
return_cont()
An opaque continuation

 下面先来看看erl_scan:string这个方向

{ok,Data} = prim_file:read_file("sn.txt").
{ok,<<"{rssAPVg}.\r\nrssAPVg1.\r\nrssAPVg2.\r\nrssAPVg3.">>}
Data1 = binary_to_list(Data).
"{rssAPVg}.\r\nrssAPVg1.\r\nrssAPVg2.\r\nrssAPVg3."

 这是我sn.txt文件放的内容

{ok, Tokens, _} = erl_scan:string(binary_to_list(Data)).
{ok,[{'{',1},
     {atom,1,rssAPVg},
     {'}',1},
     {dot,1},
     {atom,2,rssAPVg1},
     {dot,2},
     {atom,3,rssAPVg2},
     {dot,3},
     {atom,4,rssAPVg3},
     {dot,4}],
    4}

 erl_scan:string返回值的具体组成请看官方文档http://www.erlang.org/doc/man/erl_scan.html#type-token

erl_scan:tokens的用法差不多，下面也给一个例子

erl_scan:tokens([],binary_to_list(Data),0,text).
{done,{ok,[{'{',[{line,0},{text,"{"}]},
           {atom,[{line,0},{text,"rssAPVg"}],rssAPVg},
           {'}',[{line,0},{text,"}"}]},
           {dot,[{line,0},{text,".\r"}]}],
          0},
      "\nrssAPVg1.\r\nrssAPVg2.\r\nrssAPVg3."}

 对于erl_scan:tokens来说，需要返回值中more进行尾递归进行调用erl_scan:tokens,如

scan_tokens(Code) ->
    case erl_scan:tokens([], Code, 1) of
        {done, {ok, Token, _}, Remain} ->
            scan_tokens(Remain);
        {more, _} ->
            []
    end.

 那这个模块有什么用呢？就是为后面erlang可以把从文件读取的text转成erlang特定的term或者是动态生成erlang模块做准备