[Rd] get ...

[Gabor Grothendieck]

If access is removed it would be important to provide
an alternative first -- removing access and only providing
an alternative some time later does not seem prudent.

On Wed, Jul 2, 2008 at 10:57 AM, Luke Tierney <luke at stat.uiowa.edu> wrote:
> On Tue, 1 Jul 2008, Duncan Murdoch wrote:
>
>> On 30/06/2008 10:56 AM, Luke Tierney wrote:
>>>
>>> On Sat, 28 Jun 2008, Peter Dalgaard wrote:
>>>
>>>> Gabor Grothendieck wrote:
>>>>>
>>>>> Suppose we do this:
>>>>>
>>>>>
>>>>>> f <- function(...) environment()
>>>>>> e <- f(a = 1, b = 2)
>>>>>> ls(e, all = TRUE)
>>>>>>
>>>>> [1] "..."
>>>>>
>>>>>> e$...
>>>>>>
>>>>> <...>
>>>>>
>>>>>> class(e$...)
>>>>>>
>>>>> [1] "..."
>>>>>
>>>>> Is there any way of getting a and b given e without
>>>>> modifying f?
>>>>>
>>>>> evalq(list(...),e)
>>>>
>>>> $a
>>>> [1] 1
>>>>
>>>> $b
>>>> [1] 2
>>>>
>>>>
>>>
>>> I'm wondering though whether we should allow the internal DOTSXP value
>>> of "..." to escape to the user level.  Might be more appropriate for
>>> get(e,"..."), e$... (and as.list.environment and maybe a few other
>>> things) to give the "Error: '...' used in an incorrect context" error
>>> if the value is a DOTSXP.
>>
>> On the other hand, what Gabor sees in e is what he would see inside f:
>>
>>> f <- function(...) { ls(all=T) }
>>> f(a=1, b=2)
>>
>> [1] "..."
>> I don't think we should distinguish between user level in .GlobalEnv and
>> what a user sees inside a function he writes.  Stopping a user from seeing
>> ... inside a function would break all sorts of things.
>
> Huh??
>
> Noone is proposing that ls or exist, for example change.  ... is a
> special variable that can only be used in special contexts.  Just
> evaluating ... gives an error; get("...") used in the same context
> probably ought to as well.  What we do now is clearly wrong: return an
> undocumented object that can't be used for anyting useful (and
> reflects an internal implementation we might want to change).  We need
> to either prevent the R_DOTSXP values from leaking out or document
> them , define [ methods and figure out what they should do, etc.
> Preventing them from leaking out is the sensible thing to do.
>
> luke
>
>>
>> Duncan Murdoch
>>
>
> --
> Luke Tierney
> Chair, Statistics and Actuarial Science
> Ralph E. Wareham Professor of Mathematical Sciences
> University of Iowa                  Phone:             319-335-3386
> Department of Statistics and        Fax:               319-335-3017
>   Actuarial Science
> 241 Schaeffer Hall                  email:      luke at stat.uiowa.edu
> Iowa City, IA 52242                 WWW:  http://www.stat.uiowa.edu
>