On Mon, Jul 07, 2008 at 11:43:56PM -0500, Patrick R. Michaud wrote:
: On Mon, Jul 07, 2008 at 08:18:36PM -0700, Larry Wall wrote:
: > On Mon, Jul 07, 2008 at 07:16:05PM -0700, Patrick R. Michaud via RT wrote:
: > : Note however that TimToady on #perl6 speculated [1] that an empty return
: > : should return the Object prototype. I'm not sure the answer was
: > : resolved completely in that thread, however, so we'll go with returning
: > : 'undef' for now and wait for a more definitive answer before closing
: > : this ticket.
: >
: > A C<return> just returns its argument list as a Capture, so it's
: > probably just returning the "null" Capture, presumably with Object
: > (undef) in the scalar slot and an empty list in the list slot and
: > an empty hash in the hash slot.
:
: By "(undef)" here did you mean simply that it's an undefined
: Object (prototype), or that the C<undef> function now returns
: Object instead of Failure (S02:872)?
Hmm, well, on further reflections, it should in all likelihood be
neither of those. I can argue that it should be a special failure type
to try to get an item from a null list: "Attempt to pull a rabbit out
of an empty hat" or some such. :)
I can also argue that a null list in item context simply promotes to
an empty array just as a list of 2 or more elements does. Given that
"return;" is not the same as "fail;", that's probably the right thing to
do.
It does treat single-item lists as special, but note that .[0] is
a no-op on a non-array. And it's really the .[0] operation that
translates to the pull-a-rabbit-out-of-an-empty-hat failure if you
hand it a null list. Well, it's probably really "Subscript out of
range"...
Which argues that bare return should be treated as returning a list
that happens to be empty (via the Capture that return always returns
to keep the return value contextually lazy).
So
$x = nothing(); # = []
@x = nothing(); # = ()
%x = nothing(); # = ()
if nothing() {...} # always false
$x = nothing()[0] # "Subscript out of range" failure
In other words, I think I'd like to not encourage people to use bare
return to indicate failure.
Larry
