Re^5: 'xor' operator is not a sibling to 'or' and 'and'?

Perl has no Boolean type, it is interpreting values in boolean context, (which is a specialized scalar context).

There are only two default scalars 1 and ""/0 (i.e. !!1 and !!0) in case a Boolean result needs to be generated, like when using not (sic)

The extra behaviour of and/or to return the last evaluated side is closely related to short circuiting, and will by definition lead to a appropriate scalar again.

AFAIK is this feature boroughed from C, but can't be possibly extended to not or even xor

Update

That's easily proven by translating xor to a term based on and/or, since this can't be done without not

A xor B := ( A and not B) or ( B and not A)

Besides inconsistencies it's also not well defined, because the two sides of the and/or terms can be swapped (commutativity)

Cheers Rolf
_{(addicted to the Perl Programming Language :)

Wikisyntax for the Monastery
FootballPerl is like chess, only without the dice}

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Re^6: 'xor' operator is not a sibling to 'or' and 'and'? by rsFalse (Chaplain) on Dec 28, 2019 at 14:03 UTC
>> `A xor B := ( A and not B) or ( B and not A)` I only want to leave here an example: although 'logically' they return the same 'Perl-truthness', in this case they won't return same value: `perl -wle 'my( $A, $B ); print for map "[$_]", ( $A xor $B ), ( $A and + not $B or $B and not $A ); '` [download] output ('' vs. undefined): `Use of uninitialized value $_ in concatenation (.) or string at -e lin +e 1. [] []` [download]	[reply] [d/l] [select]
Re^7: 'xor' operator is not a sibling to 'or' and 'and'? by LanX (Saint) on Dec 28, 2019 at 17:06 UTC
yep `perl -MData::Dump=pp @values=("true",undef); for $A (@values) { for $B (@values) { pp [$A,$B], [ ($A xor $B), ( ($A && !$B) \|\| ($B && !$A) ) ]; } } __END__ (["true", "true"], ["", ""]) (["true", undef], [1, 1]) ([undef, "true"], [1, 1]) ([undef, undef], ["", undef])` [download] but if you apply De Morgan's law, you'll always get "default" Booleans: `perl -MData::Dump=pp @values=("true",undef); for $A (@values) { for $B (@values) { pp [$A,$B], [ ($A xor $B), !( ( !$A \|\| $B) && (!$B \|\| $A) ) ]; } } __END__ (["true", "true"], ["", ""]) (["true", undef], [1, 1]) ([undef, "true"], [1, 1]) ([undef, undef], ["", ""])` [download] Cheers Rolf _{(addicted to the Perl Programming Language :) Wikisyntax for the Monastery FootballPerl is like chess, only without the dice}	[reply] [d/l] [select]


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