Re: requiring balanced parens in a regexp?

haberg@math.su.se (Hans Aberg)
10 Nov 2006 18:38:25 -0500

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From: haberg@math.su.se (Hans Aberg)
Newsgroups: comp.compilers
Date: 10 Nov 2006 18:38:25 -0500
Organization: Mathematics
References: 06-11-039
Keywords: lex

"Peter Michaux" <petermichaux@gmail.com> wrote:


> In the following string I would like to find the word that comes after
> "test" as long as test is not inside parenthesis. In this example the
> match would be "two".
>
> "the (test one) test two"


In a lexer generator, like Flex, one can use an integer variable that is
increased for each '(' and decreased for each ')'. Then a negative number
implies a parenthesis mismatch, and top level = 0. Useful for example when
implementing nested comments, which normally should not be passed to the
parser.


--
    Hans Aberg


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