But basically I think NIL is a mild form of failure anyway, so it's

fine with me if () is a form of failure that is smart enough to be

On Sat, Sep 06, 2008 at 07:06:30PM +1100, Илья wrote:

: Hello there,

: what :foo<> should exactly produce?

: At first I was expecting:

: foo => ""

: but in Rakudo:

: foo => []

: and it looks like the right thing on the other hand.

On 2008 Sep 6, at 13:57, Larry Wall wrote:

I'm thinking () is the non-scalar (list, array, capture, maybe hash)

version of undef, which acts like a value unless you have warnings

turned on; and undef is managed as a kind of unthrown exception already,

thus so should ().

Sorry, what am I missing that I see no problem with List

always itemizing to an Array?

At YAPC::EU I pointed out to Larry that we have an adverbial form that

defaults to true:

:foo

and one that defaults to false:

:!foo

but none that defaults to undef.

After rejecting my very reasonable suggestion of:

: foo

(­ Larry then proposed that:

:foo()

should be identical to:

:foo(undef)

On Mon, Sep 8, 2008 at 11:08 AM, TSa <Thomas.Sandlass@vt­s-systems.de> wrote:

A List *does* always itemize to an Array. But parens do not a List

make; the discontinuity mentioned is syntactic.

(1,2,3) # (or longer) List

(1,2) # List

(1) # Item

() # ?

If () goes back to a List, then there's a double discontinuity in the

way parenthesized expressions are parsed.

On the other hand, there's just that sort of double discontinuity in

English pluralization, where we say "2 (or more) items", then "1

item", but then "no items". So perhaps it's justifiable in Perl6 as

well.

Ahh, I see. Thanks for the hint. It's actually comma that builds lists.

So we could go with () for undef and require (1,) and (,) for the single

element and empty list respectively. But then +(1,2,3,()) == 4.

I would also opt for () meaning empty list as a *defined* value. Pairs

that shall receive the empty list as value could be abbreviated from

:foo(()) to :foo(,). As long as the distinction between Array and List

doesn't matter one can also say :foo[], of course.

TSa wrote:

Actually, note that both infix:<,> and circumfix:<[ ]> can be used to

build lists; so [1] and [] can be used to construct single-element and

empty lists, respectively.

Actually, note that both infix:<,> and circumfix:<[ ]> can be used to

build lists; so [1] and [] can be used to construct single-element and

empty lists, respectively.

Personally, I'd like to see '()' capture the concept of "nothing" in

the same way that '*' captures the concept of "whatever". There _may_

even be justification for differentiating between this and "something

that is undefined" (which 'undef' covers). Or not; I'm not sure of

the intricacies of this. One possibility might be that '1, 2, undef'

results in a three-item list '[1, 2, undef]', whereas '1, 2, ()'

results in a two-item list '[1, 2]' - but that may be a can of worms

that we don't want to open.