Bogus warning for low priority or, or something subtle

GrandFather has asked for the wisdom of the Perl Monks concerning the following question:

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Re: Bogus warning for low priority or, or something subtle by Tanktalus (Canon) on Aug 05, 2005 at 03:40 UTC
or has a lower precedence than =. Thus, your statement is parsed as `(my $baz = $foo) or ($bar)`. Try changing $foo to 0 and see if you get what you think you should get.	[reply] [d/l]
Re^2: Bogus warning for low priority or, or something subtle by GrandFather (Saint) on Aug 05, 2005 at 04:04 UTC
Something subtle then. I obviously don't read the Precedence chart often enough :) Thank you Tanktalus Perl is Huffman encoded by design.	[reply]
Re: Bogus warning for low priority or, or something subtle by blazar (Canon) on Aug 05, 2005 at 08:29 UTC
As a general rule, that AFAICT has not been mentioned so far, the low precedence logical operators are better suited for flow control and the high precedence ones for most other things, e.g. for operating on values.	[reply]
Re: Bogus warning for low priority or, or something subtle by EvanCarroll (Chaplain) on Aug 05, 2005 at 06:17 UTC
Juxtapose this: `perl -e'print q/foo/ and q/bar/;' perl -e'print q/foo/ && q/bar/;` [download] Also see this: `perl -e'print UNDEF q/foo/ or die; perl -e'print UNDEF q/foo/ \|\| die;` [download] Evan Carroll www.EvanCarroll.com	[reply] [d/l] [select]
Re: Bogus warning for low priority or, or something subtle by basha (Initiate) on Aug 05, 2005 at 10:42 UTC
Try to do like this $baz=($foo or $baz); And then prints. It wont gives warning. $baz=$foo or $bar; "=" operator has higher precedence.so it default take $ foo value.	[reply]
Re: Bogus warning for low priority or, or something subtle by tlm (Prior) on Aug 05, 2005 at 22:25 UTC
For this sort of question I like using `B::Deparse,-p`: `% perl -MO=Deparse,-p 481076.pl Useless use of private variable in void context at 481076.pl line 10. use warnings; use strict 'refs'; (my $foo = 3); (my $bar = 2); ((my $baz = $foo) or $bar); print($baz); 481076.pl syntax OK` [download] There you have it, plain as day. Unfortunately, `B::Deparse` is not always accurate. Therefore, if necessary, I corroborate with `B::Concise`, whose output I find much harder to read than `B::Deparse`'s, but is more accurate. the lowliest monk	[reply] [d/l] [select]
Re^2: Bogus warning for low priority or, or something subtle by GrandFather (Saint) on Aug 05, 2005 at 23:12 UTC
I seem to recall seeing mention of a way of getting more verbose error and warning messages, but can't remember how. That will earn someone a ++ :) Perl is Huffman encoded by design.	[reply]
Re^3: Bogus warning for low priority or, or something subtle by tlm (Prior) on Aug 05, 2005 at 23:29 UTC
`-Mdiagnostics` [download] ? the lowliest monk	[reply] [d/l] [select]
Re: Bogus warning for low priority or, or something subtle by pg (Canon) on Aug 05, 2005 at 05:11 UTC
This is definitely interesting. I personally never noticed that or actually has a different precedency as \|\|. I don't like it, and don't think that gives anyone any real benefit. What was the thinking behind this? My guess is that, they want to give you the feeling that, \|\| is used to connect "fragments" within a "statment", and or is used to conect "statements", sort of treating Perl like a natural language. In this sense, or comes after \|\|.	[reply]
Re^2: Bogus warning for low priority or, or something subtle by GrandFather (Saint) on Aug 05, 2005 at 05:14 UTC
It's so you can: `my $importantValue = SomethingTricky () or die "A nasty thing happend\ +n";` [download] Perl is Huffman encoded by design.	[reply] [d/l]
Re^2: Bogus warning for low priority or, or something subtle by mrpeabody (Friar) on Aug 05, 2005 at 05:25 UTC
This is definitely interesting. I personally never noticed that or actually has a different precedency as \|\|. I don't like it, and don't think that gives anyone any real benefit. The different precedence is the whole point of having two "or" and two "and" operators in the first place. Read perlop under "Logical Or and Exclusive Or".	[reply]
Re^2: Bogus warning for low priority or, or something subtle by gellyfish (Monsignor) on Aug 05, 2005 at 14:26 UTC
The `or` (and `and`) was introduced with perl 5.000 as described in the Changes5.0000 : New "and" and "or" operators work just like && and \|\| but with a precedence lower than comma, so they work better with list operators. The reason that they are separate operator is to ensure "least surprise" and not to break existing code by changing the precedence of the existing operators. I guess it was also considered that it would be more expressive to have the two sets of operators with different precedence. I'm sure if you were to send a patch reversing this to p5p it would be given the consideration it deserves. /J\	[reply] [d/l] [select]
Re^2: Bogus warning for low priority or, or something subtle by halley (Prior) on Aug 05, 2005 at 14:14 UTC
I personally never noticed that `or` actually has a different precedency as `\|\|`. I don't like it, and don't think that gives anyone any real benefit. Nice attitude. The first time you encounter some feature, you not only dismiss it for yourself, but you dismiss it for everyone. Stop and think about something for its benefits before you write such a blanket statement about "anyone." -- `[ e d @ h a l l e y . c c ]`	[reply] [d/l] [select]