#!/usr/bin/env perl

use v5.10;
use strict;
use warnings;

my $space_edge = qr{
    (?(?<=      \S)     # if there is a nonspace character left
          (?!   \S)     #    then there must be no space character right
      |   (?=   \S)     #    else there must be a  space character right
    )
}x;

while (<DATA>) {
    my $edges = 0;
    for my $str ( "foo", "()" ) {
        my $qstr = quotemeta($str);

        unless (/$qstr/) {
           #print "MISSING $str in: $_";
            next;
        }

        if (/${space_edge}${qstr}/) {
            $edges++;
            print "$str EDGE LEFT:  $_"
        }

        if (/${qstr}${space_edge}/) {
            $edges++;
            print "$str EDGE RIGHT: $_"
        }

        unless ($edges) {
            print "$str UNEDGED:    $_";
        }
    }
}
exit;

__END__
Put your foo in your pocket.
Put your foo() in your pocket.
Good food was had by all.
What fools these mortals be!
food is good to have.
That's a major snafoo there.
That's a major snafoo.
That's a major snafoo
That's a major snafoo()zle
That's a major snafoo() there.
That's a major snafoo()