Re: Parsing nested parentheses

One way using regular expressions:

my $expr = '((A,B),C,(D,E))';
print extract('C',$expr),"\n";
print extract('B',$expr),"\n";
print extract('D',$expr),"\n";

sub extract {
    my $char = shift;
    my ($str,$dup) = (shift) x 2;
    1 while $dup =~ s/\([^()$char]*\)/'.' x length $&/e;
    $dup =~ m/(\([^()$char]*$char[^()]*\))/;
    return substr($str,$-[1],length $1);
}
__END__
# output:
((A,B),C,(D,E))
(A,B)
(D,E)
[download]

But you probably want to build a small expression parser.

Comment on Re: Parsing nested parentheses Download Code

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Re: Re: Parsing nested parentheses
by melora (Scribe) on Nov 18, 2003 at 18:28 UTC

Being an ancient C programmer, I would probably recurse through the string, inspecting a character at a time. A "(" would mean a call to myself with the remainder of the string. Other characters (except for ")") I would load up into a string, which would be all the stuff within a (). No, better, load them into separate strings, starting a new string after each comma. A ")" would mean returning, after inspecting the above string(s) for a match. If you find a match, I guess you print out that list, comma delimited just like it was in the original string? Or you could just print the substring (of the original string) just inspected. And yes, you could use a regex for the comparison, but you could just use "eq" to compare the strings, since the commas and parens would already be gone. To a true Perl programmer, this is probably brute force and ignorance, but I've used this approach before and it can work.

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