Flex/Bison: Bad token management?

Question

I've a problem in my lexer and in my parser.

First, in my lexer I've a line like that:

"if"    beginScope(stOTHER); return IF;

And in my parser:

stmt: IF '(' exp ')' stmts
...
stmts: stmt
       | '{' stmt_list '}'
       | '{' '}'

In a code like that:

if(sth) {
    dosth;
}

if(other) {
    doothersth;
}

beginScope will be called two times, because ( I think ) Bison don't know where is the end of the if statement, so when it found the IF token, he takes that as the end of the if statement, and read it a second time to start the other if statement...

Please help me...

Can you call `beginScope()` for "{" in your Flex file? That way, you can `endScope()` when you see "}". Just have these single-character expressions return a token like OPENBRACE and CLOSEBRACE to Bison. — chrisaycock, May 14 '12 at 19:23
No I can't, because beginScope needs a type in parameter, and there is not always a "{" as you can see — Unarelith, May 14 '12 at 19:39
Move the `beginScope` operation into your parser actions. Use a [mid-rule action](http://www.gnu.org/software/bison/manual/html_node/Mid_002dRule-Actions.html) if necessary. The lexer must not have side effects, for exactly the reason you have discovered. — zwol, May 14 '12 at 20:19

score 1 · Accepted Answer · answered Feb 28 '13 at 06:16

1

As Zack mentioned in the comments, you should call beginScope from a parser action:

stmt: IF { beginScope(stOTHER); } '(' exp ')' stmts

answered Feb 28 '13 at 06:16

vitaut

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Flex/Bison: Bad token management?

1 Answers1