On Sat, Apr 05, 2008 at 01:41:02PM -0500, John M. Dlugosz wrote:
> Larry Wall larry-at-wall.org |Perl 6| wrote:
>> On Wed, Apr 02, 2008 at 06:08:55PM -0700, Jon Lang wrote:
>> : In "Question on your last change to S02", Larry Wall wrote:
>> : > (By the way, you'll note the utility of being able to talk about a
>> : > postfix by saying .[], which is one of the reasons we allow the optional
>> : > dot there. :)
>> : : Can I take this as an indication that the rules for postcircumfix
>> : operators are an extension of the rules for postfix operators?
>>
>> Yes, postcircumfixes are just strange postfixes, syntactically
>> speaking. Semantically they may do strange things such as behave
>> more like macros than operators, of course. Certainly .() is highly
>> magical that way, and maybe subscripts too.
>>
>> Larry
>>
> Magical how?
I only mean that you can't simply rewrite
$foo.($bar)
as
$foo.postcircumfix:<( )>.($bar)
and think you've gotten anywhere, since you'd then have to rewrite it
again:
$foo.postcircumfix:<( )>.postcircumfix:<( )>.($bar)
$foo.postcircumfix:<( )>.postcircumfix:<( )>.postcircumfix:<( )>.($bar)
...
Something has to recognize it as a special form.
> I take it that the macro-like behavior is in how the circumscribed text is
> parsed, and once that has been collected, it behaves just like a function
> call to a function named postcircumfix:<( )> etc.?
>
> And if I create a function named postcircumfix:<[ ]> (or one of the
> others), I get the _same_ magic as normally applied to subscripts? If it's
> a matter of defining the argument as @@ (for subscripts) or Capture (for
> function-call syntax), that's not magic.
Well, it's possible the subscript itself isn't the magical part there.
At minimum, the semilist rule probably needs to recognize @@ and ** at the
top level (or @@ and ** need to recognize that they're at the top
level of a context that wants them to interpolate multiple dimensions
rather than just one).
It's also possible that even this amount of syntactic magic is evil,
but I'd like [1;**;3] to know it has an arbitrary number of dimensions,
while [1;$two;3] should know that it has exactly three dimensions even
if $two happens to contain ** or @@.
It's also possible I'm just nuts, and slice context should be a purely
run-time activity.
Larry
