Perhaps this example should be provided somewhere as a 'gotcha'.
On Mon, Jul 3, 2017 at 11:09 AM, jn...@jnthn.net via RT <
perl6-bugs-follo...@perl.org> wrote:
> On Mon, 03 Jul 2017 05:46:46 -0700, comdog wrote:
> > It seems that term precedence with << >> gets confused.
> >
> The << >> quoting construct interpolates. The rule for interpolation of
> method calls, indexing, etc. after a scalar is that there may be one, but
> it may only end with a ], ), } or >.
>
> > {
> > my $number = <<$string>>[0];
>
> When the variable is encountered inside of the interpolating quoting
> construct, which is being parsed by the quoting parser, it calls back into
> the Perl 6 main language parser. This parses a variable and optionally a
> postfix. The >>[0] is a valid postfix, where >> is the hyper-operator and
> [0] is the indexer. Therefore the $string>>[0] is taken as the thing to
> interpolate. It then hands back control to the quoting parser.
>
> > put "Type: " ~ $number;
> > #`(
> > ===SORRY!=== Error while compiling ...
> > Cannot use variable $number in declaration to initialize itself
> > ------> put "Type: " ~ $⏏number;
>
> This is complaining that $number was used before its declaration was
> complete, which is indeed the case because at we are still inside of the
> quoting construct.
>
> I can see the potential for a human reader to be confused, but the Perl 6
> parser is not in the least bit confused. There isn't any question as to
> what will parse the >>: if the main language parser understands it and
> wants it, then it gets it, because the quoting parser doesn't get a say
> again until the main language parser has done its bit. This is the same
> reason that you can do stuff like:
>
> say "Foos: @foo.join("bar")"
>
> And there isn't a bit of confusion so far as Perl 6 is concerned that the
> inner " is opening a new string, not closing the one we were already in.
> Granted it's maybe kinder to the reader to write it with single quotes
> inside of the string. But nestings of main language => quote parser => main
> language => quote parser will Just Work, each eating as much as it
> understands (or until seeing its terminator) before giving up control.
>
> /jnthn
>
>
--
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