[j-nsp] negation operator in SLAX

[Martin T]

On Mon, Jun 18, 2018 at 9:40 PM Phil Shafer <phil at juniper.net> wrote:
>
> Martin T writes:
> >Oh, yes. I forgot the not() function. I made a small comparison
> >between not(), jcs:empty() and ! using five data types in SLAX:
>
> "!" and "not" are identical.  The "!" is just syntactic sugar that
> turns "! x " into "not(x)", as you can see in the code:
>
> https://github.com/Juniper/libslax/blob/master/libslax/slaxparser-xp.y#L164
>
> >5) Empty RTF:
> >"not( $rtf )" returns false, which is an expected result because even
> >an empty RTF converts to true. "jcs:empty( $rtf )", to my surprise,
> >returns true. According to documentation, RTF is always considered to
> >not be empty. "! $rtf" returns false.
>
> RTFs are exactl the reason I made jcs:empty(), since it bugs me
> that boolean($rtf) is true.
>
>   http://juniper.github.io/libslax/slax-manual.html#slaxis-empty
>
> And "bugs" is too weak a word.  Imho, RTFs are the chief source of
> slax/xslt violations of the Principal of Least Astonishment.
>
>     % cat /tmp/foo.slax
>     version 1.2;
>
>     var $a := <a> {
>       <b> "b";
>     }
>
>     main <top> {
>         var $x = { copy-of $a/z; }
>         var $y = $a/z;
>
>         <x> boolean($x);
>         <y> boolean($y);
>     }
>     % slaxproc -g -E /tmp/foo.slax
>     <?xml version="1.0"?>
>     <top>
>       <x>true</x>
>       <y>false</y>
>     </top>
>
> See also the ":=" assignment operator, which helps avoid RTFs:
>
>   http://juniper.github.io/libslax/slax-manual.html#colon-equals
>
> Thanks,
>  Phil

Again, thank you for explaining this Phil!


Martin