On at least two occasions (but not very many more than that) I've written code like:

    if(  !$a == !$b  ) {
#or
    if(  !$x != !$y  ) {
[download]

and those could now be rewritten:

    if(  not $a xor $b  ) {
#or
    if(  $x xor $y  ) {
[download]

but I don't adopt new Perl features lightly and I haven't written Perl code that wanted that sort of test since I noticed the existance of xor so I've never used xor, just written code where I would have used it had it been available enough at the time.

Though, I actually find the concept of "these two logical expressions are equal" to be more useful/natural than a logical "xor" (not equal) so I'm more likely to want

    if(  !$a == !$b  ) {
[download]

than the other case and I'd probably leave that as-is rather than change it to

    if(  not $a xor $b  ) {
[download]

because I find the latter harder to understand. So I'd probably rather have an eqv (pronounced "equivalent") over an xor. (:

                - tye