I came up with this recursive-regex code. It's a bit simpler than most of the others posted here. It finds the leftmost longest palindrome in each line.
my $palin_re;
$palin_re = qr/(([a-z]) # First letter
[^a-z]* # any irrelevant chars
(?:(??{$palin_re})|[a-z]?) # The interior
[^a-z]* # any other irrelevant chars
\2) # the last letter matches the first
/xi;
while (<DATA>) {
if (/\b$palin_re\b/) {
print "Matched $1\n";
}
else {
print "No palindrome found in '$_'\n";
}
}
__DATA__
oo
madam in eden, I'm Adam, prince of eternia
is god a dog?
nested testest detsen nested
i prefer pi ip referp
nothing to see here, folks.
Caution: Contents may have been coded under pressure.