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Postings from July 2013
On Wed, Jun 26, 2013 at 09:59:02PM -0400, Ricardo Signes wrote:
> We can add postfix syntax for dereferencing to work in *all* places that we
> might dereference, creating a construct that is clearly syntactically an array
> (or hash, etc.) when needed.
>
> push $x->{foo}->[0]->m->@*, $y;
>
> push @y, $x->{foo}->[0]->m->@*;
>
> subroutine( $x->{foo}->[0]->m->@* )
>
> print $delivery->{email}->body_string_ref->$*;
I would be pleased to have a syntax that can be used anywhere that a
circumfix can be used. It avoids learning/remembering a special case about
where it works, and where it doesn't.
I'm going to assume that the wording defining prototypes would need to be
carefully re-written to find a clear terse way to say that
sub foo(\@@);
foo $x->{foo}->[0]->m->@*, $y;
is considered to have an @ at the front of that first argument, so that
the above code is legal.
> If we want the two forms to be really of equivalent value, we'll also need to
> be concerned with:
>
> print "Things: $aref_of_things->@*"
>
> ...which gets into less clearly-introduceable behavior.
This is "less clear" because right now that parses as
print 'Things: ' . $aref_of_things . '->@*'
not as a syntax error? ie we're changing the meaning of something valid.
> Finally, do we need to enable postfix slices? I think that if we can, we
> should. I think the syntax is free.
>
> say for $href->{aref}->@[ 0, 2, 4 ];
>
> say for $aref->[ $h_idx ]->@{ qw(foo bar baz) };
>
> I think we have a few options for the specific tokens to put after that last
> arrow. I think $* and @* and so on work well. Replacing the splat with a
> colon has been suggested as well. The point here is to provide the feature.
> It's not about reducing total punctuation. This is Perl, and we must embrace
> our punctuation! It's about simplifying the reading of code by allowing it to
> be read and written linearly.
Are there parsing ambiguities with a colon? Particularly, if a colon is
expected because the opening '?' of a ternary has been seen, does this
confuse things? Perl 6 initially doubled the symbols of '?' and ':' to enable
':' to be used in a lot more places. (and then changed '::' to '!!' I think
to further reduce ambiguities)
I'm not sure that ':' is equal to '*'. Whilst both are currently valid for
a scalar splat syntax:
$ perl -le '$a = bless []; *{""} = sub {warn "Hi!"}; print $a->$*'
$* is no longer supported at -e line 1.
Hi! at -e line 1.
1
$ perl -le '$a = bless []; *{" \n-"} = sub {warn "Hi!"}; print $a->$:'
Hi! at -e line 1.
1
Existing code that uses $* warns. $: doesn't.
Nicholas Clark
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