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Asked: 2026-05-15T02:58:06+00:00

I am writing a simple parser for C. I was just running it with

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I am writing a simple parser for C. I was just running it with some other language files (for fun – to see the extent of C-likeness and laziness – don’t wanna really write separate parsers for each language if I can avoid it).

However the parser seems to break down for JavaScript if the code being parsed contains regular expressions…

Case 1:
For example, while parsing the JavaScript code snippet,

var phone="(304)434-5454"
phone=phone.replace(/[\(\)-]/g, "") 
//Returns "3044345454" (removes "(", ")", and "-")

The ‘(‘, ‘[‘ etc get matched as starters of new scopes, which may never be closed.

Case 2:
And, for the Perl code snippet,

 # Replace backslashes with two forward slashes
 # Any character can be used to delimit the regex
 $FILE_PATH =~ s@\\@//@g;

The // gets matched as a comment…

How can I detect a regular expression within the content text of a “C-like” program-file?

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1 Answer

  1. Editorial Team

    It is impossible.

    Take this, for example:

    m =~ s/a/b/g;

    Could be both C or perl.

    One minute’s thinking reveals, that the number of perl style regular expressions that are also sntyctically valid C expressions is infinite.

    Another example:

    m+foo *bar[index]+i

    The best you can get is some extreme vague guesswork. The difficulty stems from the fact that a regular expression is a sequence of characters that can be virtually everything.

    You better clean up your error handling. A parser should not “break down” if some parenthesis are missing or superfluous ones are seen.

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