Warning: Use of "rand" without parentheses is ambiguous at mytest.pl line 4 (#1)
    (S ambiguous) You wrote a unary operator followed by something that
    looks like a binary operator that could also have been interpreted as a
    term or unary operator.  For instance, if you know that the rand
    function has a default argument of 1.0, and you write

        rand + 5;

    you may THINK you wrote the same thing as

        rand() + 5;

    but in actual fact, you got

        rand(+5);

    So put in parentheses to say what you really mean.

##</code><code>##

use strict;
use warnings;
use diagnostics;

my $string = "1230000000";

print $string =~ m/123(?{(pos <= length($_)*.5) ? '(?=)':'(?!)'})(??{$^R})/
    ? "Matched.\n"
    : "Didn't match.\n";

__OUTPUT__
Warning: Use of "pos" without parentheses is ambiguous at (re_eval 2) line 1 (#1
)
    (S ambiguous) You wrote a unary operator followed by something that
    looks like a binary operator that could also have been interpreted as a
    term or unary operator.  For instance, if you know that the rand
    function has a default argument of 1.0, and you write

        rand + 5;

    you may THINK you wrote the same thing as

        rand() + 5;

    but in actual fact, you got

        rand(+5);

    So put in parentheses to say what you really mean.

panic: top_env

##</code><code>##

panic: restartop 
(P) Some internal routine requested a goto (or something like it), and didn't supply the destination.