On Aug 9, 2013, at 12:32 PM, Jakub Zawadzki <[email protected]> wrote:
> On Fri, Aug 09, 2013 at 11:41:59AM -0700, Gerald Combs wrote:
>> Laura Chappell and Sean Walberg recently discovered that logical OR
>> takes precedence over logical AND in display filters. Is there any
>> reason we shouldn't reverse this so that we match the order of
>> operations elsewhere (including BPF)?
>
> I think in BPF they have the same priority, evaluated from left to right,
> check dump of:
>
> 'port 333 or port 444 and host 192.168.192' same '(port 333 or port 444) and
> host 192.168.192.1'
> 'host 192.168.192.1 and port 443 or port 333' same '(host 192.168.192.1 and
> port 443) or port 333'
Yup. To quote the pcap-filter man page:
Alternation and concatenation have equal precedence and associate left
to right.
C (and, unless somebody was insane, C++ and Objective-C and Objective-C++) give
logical AND a higher precedence than logical OR.
And, for those curious about FORTRAN:
http://www.fortran.com/F77_std/rjcnf0001-sh-6.html#sh-6.4.2
.AND. has a higher precedence than .OR..
Continuing:
Perl:
http://perldoc.perl.org/perlop.html#Operator-Precedence-and-Associativity
"and" has a higher precedence than "or".
Python:
http://docs.python.org/2/reference/expressions.html#operator-precedence
same (the list goes from *lowest* precedence to *highest* precedence).
JavaScript:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Operator_Precedence#Table
same.
In Ada 95, they seem to have the same precedence:
http://www.infres.enst.fr/~pautet/Ada95/chap04.htm
Pascal appears to give AND a higher precedence than OR:
http://www.tutorialspoint.com/pascal/pascal_operators_precedence.htm
I have the sneaking suspicion that we may have one of the few, if not the only,
expression languages where logical OR takes precedence over logical AND, in
which case that's probably the wrong thing to do, by the Principle Of Least
Surprise if nothing else. The only reason to keep our current behavior would
be backwards compatibility.
If we decided to change the precedence, the remaining question is whether to be
like C (and languages that have followed C) or like libpcap?
___________________________________________________________________________
Sent via: Wireshark-dev mailing list <[email protected]>
Archives: http://www.wireshark.org/lists/wireshark-dev
Unsubscribe: https://wireshark.org/mailman/options/wireshark-dev
mailto:[email protected]?subject=unsubscribe
