Actually, let's try a simpler one:
pyanfar Z$ 6 'say ([5])[0]'
5
The list [5] understands Positional, and therefore knows about what to do
with the [0]. The parentheses are only because [5][0] looks a bit strange;
but that one works the same way.
The same is true of the list that words() produces. words() doesn't need to
know that, it just gives you a list. Positional describes the "indexable"
attribute of a list.
(If you look up List in the type documentation, you will see other roles
like Iterable that lists know about.)
On Wed, Sep 26, 2018 at 10:11 PM Brandon Allbery <allber...@gmail.com>
wrote:
> That's not helping. What didn't you understand? Are you still expecting
> that it is words() that must know all the details of what a list is,
> because a list can't know what itself is?
>
> On Wed, Sep 26, 2018 at 10:09 PM ToddAndMargo <toddandma...@zoho.com>
> wrote:
>
>> On 9/26/18 7:04 PM, Brandon Allbery wrote:
>> > It doesn't. It just improves error messages.
>> >
>> > words() produces a list-like thing; that's what really matters, because
>> > list-like things do the Positional role. Declaring it up front lets
>> Perl
>> > 6 give you an error message early if you use the result in the wrong
>> way
>> > or if the actual implementation of words() doesn't produce something
>> > that does the Positional role.
>> >
>> > pyanfar Z$ 6 'say (sub { [5] })()[0]'
>> > 5
>> >
>> > I didn't declare the anonymous sub as producing a Positional; it just
>> > returns a List. I then invoke it with (), and apply [] to the resulting
>> > List. It's the fact that it produced a List that matters; any List or
>> > Seq or Array or Buf, etc. can be []-ed,because they all do the
>> > Positional role that defines [].
>>
>> Uhhh okay.
>>
>
>
> --
> brandon s allbery kf8nh
> allber...@gmail.com
>
--
brandon s allbery kf8nh
allber...@gmail.com
