On Thu, Jul 06, 2006 at 01:21:08AM -0700, Allison Randal wrote:
> The problem is really that we're trying to simultaneously a) refer to
> the root HLL namespace directly, and b) pretend that it doesn't exist.
I don't think (b) is quite true. It's more that we're avoiding explicit
re-coding of a known bit of environmental information, as in "the first
floor of this building" rather than "the first floor of 123 main street".
> Chip Salzenberg wrote:
> >Allison, what do you think of zero-length keys, i.e. having [] construct a
> >Key PMC describing no dimensions of lookup? If we use those we can get rid
> >of the current null-string hack.
>
> Fundamentally altering the way keyed access works seems like a pretty
> extreme solution when the problem is just "the root HLL namespace
> doesn't have a name".
I brought it up partly because I was hoping you'd say something like, "Oh
yeah, we're gonna need zero-length keys anyway for Perl 6". What is the
parameter to operator:postcircumfix [] when a user says
@array.[]
?
> It's simpler to give the root HLL namespace a name.
Indeed, it already has the name of "empty list" when a PMC array is the
naming vehicle:
$P0 = new .FixedPMCArray
$P1 = get_namespace $P0 # that's the HLL root
There are two kinds of lists in play for namespaces; one of them can have a
length of zero (PMC array), but the other one can't (key), and the one that
can be zero-length doesn't have convenience pasm syntax.
> A null string could be canonized as the "name" of the root namespace,
> though something a little more meaningful and easier to type would be nice.
I should emphasize that I've gone to the recent trouble of making namespace
[''] *not* mean the HLL root for two reasons: (1) it's poor manners on the
part of a VM to steal names from HLLs or users, and (2) when a user is
working with an array of names, they'll want to be able to decompose the
list -- which puts a string that used to be in the middle out on the front,
or by itself -- without accidentally re-rooting the search.
Possibility: If we introduce a pasm keyword Null to mean a pmc constant null
(and perhaps a string contant null), then the null name could be easier to
type. It could also be useful in other contexts.
Gentle observation: [] is pretty easy to type, and offers consistency:
$P2 = get_namespace ['a','b'] # two levels from root
$P1 = get_namespace ['a'] # one level from root
$P0 = get_namespace [] # zero levels from root
Ugly hack / joke: If you were willing to look the other way, [] could be an
alternative spelling for PMC Null. :-P
--
Chip Salzenberg <[EMAIL PROTECTED]>
