Perl logical operators

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

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Re: Perl logical operators by choroba (Cardinal) on Jul 18, 2018 at 06:47 UTC
`true` and `false` are barewords with no special meaning in Perl. Moreover, you should use strict: it would have told you `Bareword "false" not allowed while "strict subs" in use at - line 1. Bareword "true" not allowed while "strict subs" in use at - line 2.` [download] The common value used for true is 1, for false, you can use 0, "" or undef. Also, $a and $b are special variables used in sort, it's better not to use them anywhere else. `#!/usr/bin/perl use warnings; use strict; my $A = 0; my $B = 1; print "Value of \$A = $A and value of \$B = $B\n"; my $c = ($A and $B); print "Value of \$A and \$B = $c\n"; $c = ($A && $B); print "Value of \$A && \$B = $c\n"; $c = ($A or $B); print "Value of \$A or \$B = $c\n"; $c = ($A \|\| $B); print "Value of \$A \|\| \$B = $c\n"; $A = 0; $c = not($A); print "Value of not(\$A)= $c\n";` [download] ($q=q:Sq=~/;[c](.)(.)/;chr(-\|\|-\|5+lengthSq)`"S\|oS2"`map{chr \|+ord }map{substrSq`S_+\|`\|}3E\|-\|`7**2-3:)=~y+S\|`+$1,++print+eval$q,q,a, [download]	[reply] [d/l] [select]
Re: Perl logical operators by tobyink (Canon) on Jul 18, 2018 at 07:23 UTC
In addition to what choroba said, if you really want to be able to use the keywords `true` and `false` in your script, there are a few CPAN modules which will provide them for you, such as boolean. Or you can just define them as constants. `use constant {qw( true 1 false 0 )};` [download] toby döt ink	[reply] [d/l] [select]
Re^2: Perl logical operators by tweetiepooh (Hermit) on Jul 10, 2019 at 13:38 UTC
When did this form become valid? I used on my dev box (5.28) but on production (5.16) I get a syntax error and need to use `use constant {true=>1,false=>0}`	[reply] [d/l]
Re^3: Perl logical operators by choroba (Cardinal) on Jul 10, 2019 at 13:49 UTC
Interestingly, it's a difference in Perl parser, not in constant. As usually, help the parser by telling it the `{` doesn't start a block, but a hash reference: `use constant +{ qw( true 1 false 0 ) };` [download] `map{substr$_->[0],$_->[1]\|\|0,1}[\\|\|{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^ARGV,3]`	[reply] [d/l] [select]
Re^3: Perl logical operators by hippo (Archbishop) on Jul 10, 2019 at 13:48 UTC
perldelta for 5.18.0 says: use no longer tries to parse its arguments as a statement, making `use constant { () };` a syntax error (perl #114222). which I believe refers to this.	[reply] [d/l]
Re: Perl logical operators by AnomalousMonk (Archbishop) on Jul 18, 2018 at 13:02 UTC
See also Truth and Falsehood in perlsyn for more on truthyness in Perl. Give a man a fish: `<%-{-{-{-<`	[reply] [d/l]
Re: Perl logical operators by ikegami (Patriarch) on Jul 18, 2018 at 11:19 UTC
Always use `use strict; use warnings qw( all );`!!!	[reply] [d/l]
Re^2: Perl logical operators by Anonymous Monk on Jul 18, 2018 at 12:32 UTC
Idly wondering why this hasn't become the default ...	[reply]
Re^3: Perl logical operators by hippo (Archbishop) on Jul 18, 2018 at 12:40 UTC
We went through all that more than a decade ago: Why isn't C<use strict> the default?	[reply]
Re^4: Perl logical operators by roboticus (Chancellor) on Jul 18, 2018 at 17:32 UTC
Re^5: Perl logical operators by Your Mother (Archbishop) on Jul 18, 2018 at 18:51 UTC
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Re^5: Perl logical operators by Anonymous Monk on Jul 19, 2018 at 09:21 UTC
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Re^3: Perl logical operators by haukex (Archbishop) on Jul 18, 2018 at 18:06 UTC
Idly wondering why this hasn't become the default ... Well, at least there's this: `use 5.012;` and up enables strict. Backwards compatibility is a big thing with Perl 5, and hence there are often fairly long deprecation cycles for incompatible changes, and if one wants to use the newer features of the new Perl versions, `use VERSION;` is an easy way to do that. See also use and feature.	[reply] [d/l] [select]