Lex：多个文件，不同的规则

发布于 2024-11-04 20:24:32 字数 328 浏览 0 评论 0原文

我必须解析多个文件，每种情况都有不同的规则。也就是说：我需要一些规则在处理文件时起作用，然后再禁用。

我可以简单地使用全局变量来跟踪程序的状态，并让我的规则在其体内决定是否执行任何有用的操作，如下所示：

%{
    static int state;
%}

%%
{something} {
    if (state == SOMETHING_STATE) ...
}

{something_else} {
    if (state == SOMETHING_ELSE_STATE) ...
}
%%

不过，我猜有更好的方法可以做到这一点。有没有？

原文

I have to parse more than one file, with different rules for each case. That is: I need some rules to work when processing a file, and be disabled afterwards.

I could simple use a global variable to track the state of the program, and have my rules decide inside their body whether to do anything useful or not, like this:

%{
    static int state;
%}

%%
{something} {
    if (state == SOMETHING_STATE) ...
}

{something_else} {
    if (state == SOMETHING_ELSE_STATE) ...
}
%%

I'm guessing there's a better way to do this, though. Is there?

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青柠芒果 2024-11-11 20:24:32

您需要启动状态 - 基本上 lex 有一个内置的 state 变量，您可以将规则注释为仅在某些状态下触发

%s state1
%s state2
%s state3

%%

<state1>{something}    { // this rule matches only in state1
                         // change to state2
                         BEGIN(state2); }

<state1,state3>{something_else}   { // this rule matches in state1 or state 3 }

{more_stuff}        { // this rule matches in all states }

您可以在任何 lex 或 flex 书籍中或在在线 Flex 文档

You want start states -- basically lex has a builtin state variable and you can annotate rules as only firing in certain states

%s state1
%s state2
%s state3

%%

<state1>{something}    { // this rule matches only in state1
                         // change to state2
                         BEGIN(state2); }

<state1,state3>{something_else}   { // this rule matches in state1 or state 3 }

{more_stuff}        { // this rule matches in all states }

You can find documentation on this in any lex or flex book, or in the online flex documentation

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暖阳 2024-11-11 20:24:32

假设您使用的是 Flex 之类的东西而不是原始的 lex，您可以使用开始状态。当您解析的内容会改变解析方式时，您会输入一个状态来执行该解析，并使用该状态标记适当的规则。当你解析任何标记该状态结束的内容时，你会执行另一个操作：

{state_signal} { BEGIN(STATE2); }

<STATE2>{something} { handle_something(); }

<STATE2>{state3_signal} { BEGIN(STATE3); }

<STATE3>{something} {handle_something2(); }
<STATE3>{whatever} { BEGIN(START); }

Assuming you're using something like Flex rather than the original lex, you can use start states. When you parse something that changes how you do the parsing, you enter a state to do that parsing, and you tag the appropriate rules with that state. When you parse whatever marks the end of that state, you go do another:

{state_signal} { BEGIN(STATE2); }

<STATE2>{something} { handle_something(); }

<STATE2>{state3_signal} { BEGIN(STATE3); }

<STATE3>{something} {handle_something2(); }
<STATE3>{whatever} { BEGIN(START); }

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