support of `substitute(...())`

Note that substitute(...()) and substitute(someFunc(...))[-1] give 
slightly different results, the former a pairlist and the latter a call.
 ? > str((function(...)substitute(...()))(stop(1),stop(2),stop(3)))
 ? Dotted pair list of 3
 ? ?$ : language stop(1)
 ? ?$ : language stop(2)
 ? ?$ : language stop(3)
 ? > 
str((function(...)substitute(someFunc(...))[-1])(stop(1),stop(2),stop(3)))
 ? ?language stop(1)(stop(2), stop(3))

The ...() idiom has been around for a long time, but more recently 
(slightly after R-3.4.0?) the ...elt(n) and ...length() functions were 
introduced so you don't have to use it much.  

I don't see a ...names() 
function that would give the names of the ... arguments - 
names(substitute(...())).

Bill Dunlap
TIBCO Software
wdunlap tibco.com <http://tibco.com>


On Thu, Mar 12, 2020 at 2:09 AM D?nes T?th <toth.denes at kogentum.hu 
<mailto:toth.denes at kogentum.hu>> wrote:

    Dear R Core Team,

    I learnt approx. two years ago in this mailing list that one can use
    the
    following "trick" to get a (dotted pair)list of the ellipsis arguments
    inside a function:

    `substitute(...())`

    Now my problem is that I can not find any occurrence of this call
    within
    the R source - the most frequent solution there is
    `substitute(list(...))[-1L] `

    I would like to know if:
    1) substitute(...()) is a trick or a feature in the language;
    2) it will be supported in the future;
    3) when (in which R version) it was introduced.

    A hint on where to look for the machinery in the R source would be also
    appreciated.

    Regards,
    Denes