#!/usr/bin/perl -w

use strict;

my $a;

$a = q{
   foreach (1..2) {}
   print "Reachable?\n";
};

'a' =~ /a(?{eval$a})/;

$a = q{
   map {} foreach 1..2;
   print "Unreachable?\n";
};

'a' =~ /a(?{eval$a})|b(?{syntax error})/;

0 ?
(
   unreachable
   syntax error
)
:
(
   print "Reachable\n"
);

'a' =~ /b(?{print "NO\n"})|a(?{print "Reachable\n"})|a(?{print "NO\n"})/;