You're right. Bitwise operators are the only place where there's a difference between strings and numbers. BTW This difference does not fit into the philosophy of Perl, where you should not be able to distinguish between strings and numbers, so this is actually a language design flaw.

You could detect if a scalar is a string or a number, without resorting to XS, by making use of this different behavior. If you use bitwise XOR (^) and XOR a scalar with itself, you'll get the value 0 if it was a number, and a string of null bytes ("\0") with the original string length of the argument, if it was a string. Yes, even if the number doesn't fit into an integer, like 1E99.

I think this will work:

sub is_number {
     my $arg = shift;
     return defined $arg && !ref $arg && ($arg^$arg) eq '0';
}
[download]

BTW dual-vars, like !1, are treated as a number.

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