On Sat, Mar 26, 2005 at 11:57:48PM -0500, Uri Guttman wrote:
: >>>>> "LW" == Larry Wall <[EMAIL PROTECTED]> writes:
:
: LW> That being said, in Perl 5, if you say
:
: LW> @a = undef;
:
: LW> you don't get an undefined array. I'd like to make undef smart enough
: LW> about list contexts that @a actually does end up undefined in Perl 6.
: LW> That is, in scalar context, undef is a scalar value as in Perl 5, but
: LW> in Perl 6, undef in list context means "there isn't anything here if
: LW> you try to look for it", so it's more like () in Perl 5, except that
: LW> it also undefines the array if it's the only thing in the array.
:
: then how would you assign undef to the only element of the array? would this
: be needed:
:
: @a = ( undef ) ; # same as p5?
:
: vs.
: @a = undef ; # like undef @a in p5?
Those would do the same thing under the current proposal, since
they're both in list context. If you really, really want a scalar
undef value in list context, you could always say
@a = scalar(undef);
: i have always railed against undef on aggregates as it leads to using
: defined on them which is not the same as checking if an aggregate has
: any elements. i see that often in newbie code.
Well, let's not confuse Perl 5's shortcomings with Perl 6's. I think
we should fix the problem by making undef work a little more like the
newbie expects, which is context dependent.
: in fact i would like to
: stop allowing undef as a function with args and have it only return a
: scalar undef value. there should be a different op to truly make an
: aggregate undefined (and i still don't see a need for that, emptying it
: is all that i ever think is needed).
We could certainly split out a separate undefine() function. We could
even give it an optional argument that says *why* it's undefined, turning
it into an unthrown exception, basically. We could use such a function
to create interesting values of undef that are context sensitive.
: in my world undef is a scalar value and nothing else. how do you see it
: in p6?
undef is not a scalar value, it is the explicit *absence* of a value
where you expected one. In Perl 6, undef is the Bearer of Bad News.
If you merely want undef for a scalar placeholder without negative
connotations, I'd suggest something like
class Empty {}
my $nada = new Empty;
instead. And $nada is the same length as undef. $X would be even
shorter.
On the other hand, Perl 6 is consistently returning booleans as
0 and 1 rather than "" and 1, so it's likely that constant 0 and 1
can be stored in "less than a bit", as it were. So there might even
be some kind of zero type that's essentially a value that's always 0,
and takes no room to store at all. That might serve as a pretty good
neutral placeholder.
Larry
