As Fletch mentioned, the trick is to use the (?{code}) assertion. Increment the current depth when entering the recursion (left parenthesis in the example), decrement it when leaving (right parenthesis). When incrementing, store the maximum.
#!/usr/bin/perl
use warnings;
use strict;
use feature qw{ say };
my $string = '((()))(((())))(()(()))';
my $max = 0;
my $depth = 0;
if ($string =~ /^(
\(
(?{$max = $depth if ++$depth > $max})
(?1)*
\)
(?{--$depth})
)
(?1)*
$/gx
) {
say $max;
}
map{substr$_->[0],$_->[1]||0,1}[\*||{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^*ARGV,3]
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How (Not) To Ask A Question
I'd guess you could maybe do something with embedding something like (?{$depth++}) somewhere but lacking a concrete example to work from that's pure handwavium.
The cake is a lie.
The cake is a lie.
The cake is a lie.
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