use warnings;
use strict;
use 5.010;

my ($LEFT,$RIGHT) = ('(',')');

use Regexp::Common qw/balanced/;
sub parseparens {
	my ($str) = @_;
	return $str unless index($str,$LEFT)>=0;
	$str = substr $str,1,-1 if $str=~/^\Q$LEFT\E.*\Q$RIGHT\E$/;
	return [ map {parseparens($_)}
		split /$RE{balanced}{-parens=>$LEFT.$RIGHT}/, $str ];
}

sub buildparens {
	my ($data) = @_;
	return $data unless ref $data;
	return join '', map {buildparens($_)} $LEFT, @$data, $RIGHT;
}

# $wanted gets the string elements in $_ and can manipulate them,
# if it returns false the entire arrayref
# which contains that string is filtered out
sub filter {
	my ($data,$wanted) = @_;
	if (!ref $data) {
		local $_ = $data;
		return $wanted->() ? $_ : ();
	}
	my ($keep,@out) = (1);
	for my $e (@$data) {
		if (ref $e) {
			push @out, filter($e,$wanted);
		}
		else {
			local $_ = $e;
			$keep=0 unless $wanted->();
			push @out, $_;
		}
	}
	return $keep ? \@out : ();
}

use Data::Dumper;
$Data::Dumper::Terse=1;
$Data::Dumper::Indent=0;

my $input = '(E,(A,B),(C,(X,Y,Z),D),F)';
say "   \$input = ", Dumper($input), ";";

my $parsed = parseparens($input);
say "  \$parsed = ", Dumper($parsed), ";";
warn "parse-/buildparens round trip failed: ".buildparens($parsed)
	unless buildparens($parsed) eq $input;

my $filtered = filter($parsed, sub {!/\b(?:A|C)\b/});
say "\$filtered = ", Dumper($filtered), ";";

my $output = buildparens($filtered);
$output=~s/,(?=,)//g;
say "  \$output = ", Dumper($output), ";";