A little question about "print"

[moroshko]

Hello !

Can someone explain me please why
print 3==4;
prints nothing ?

I would expect 3==4, which is false, to be converted to 0, so I expect "print" to print "0". Where am I wrong ?

Thanks !

 

[prex1]

The number 0, the strings '0' and '', the empty list (), and undef are all false in a boolean context. All other values are true. Negation of a true value by ! or not returns a special false value. When evaluated as a string it is treated as '', but as a number, it is treated as 0.

Franco

http://www.xcalcs.com

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http://www.megamag.it

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[moroshko]

Hi Franco,
Thank you for the explanation.
I agree with what you said, but still cannot understand the issue.
What do you mean by "special false value" ? Does Perl has "false value" and "special false value" ?
As I understand, 3==4 evaluates as false, but "print" expect list, so 3==4 evaluated in list context, right ?
Is there some rule that 'false' in list context is evaluated as empty list, (), and 'true' in list context is evaluated as this list: (1) ?
Thank you in advance !

 

[prex1]

That was a quote from perl documentation, so that's not me!
It's a perl rule indeed that everything that evaluates as false in a boolean operation will return something that I don't know exactly what it is (but does it matter?), but might be called a null (term that's not used by perl): once you understand that just use [tt]print 3==4?1:0;[/tt] instead.

Franco

http://www.xcalcs.com

: Online engineering calculations

http://www.megamag.it

: Magnetic brakes for fun rides

http://www.levitans.com

: Air bearing pads