in reply to 1 vs "1"

You may be able to exploit the ~ operator, it has deep knowledge of Perl's internals. For example:
$string = "1"; $integer = 1; print ~$string; # Prints an extended character print ~$integer; # Prints 4294967294
Much easier than messing with perlguts. But there's one caveat: using ~ on a string with extended characters results in ASCII characters; that is ~chr(205) is "2". Assuming your definition of "string" does not include extended characters (only ASCII), you should be able to get away with a function like this:
sub is_integer { return (~$_[0] =~ m/^[0-9]+$/) ? 1 : 0; } print "1 ", is_integer(1), "\n"; # 1 ok print "'1' ", is_integer('1'), "\n"; # 0 ok print "chr(205) ", is_integer(chr(205)),"\n"; # 1 not ok
That said, be careful with this power. You don't want to confuse your users. Problems occur when reading data from files or console, as everything read is a string unless explically changed via +0. This also doesn't work for floating point. But sometimes it may have useful uses.

Hope this helps,

Jeff Connelly