[Rd] Feature request: Allow comma after last element in a list

[@vi@e@gross m@iii@g oii gm@ii@com]

Manfred,

I don't know how much work it would be to add in a feature that was not in
the original design of S at a time when perhaps a dangling comma was not
supported widely or seen as necessary.

I note that R (as a successor to S) kept the same convention here and a
comma at the end of a line signals there is more to come and the parser
should keep looking on additional lines for more to include within the same
statement. This is different than a language like Python where indentation
is used for a level of grouping and other methods are often used to indicate
the current line should be extended.

I wonder if a work-around might make sense. What if we allowed use of a
symbol like "..." to mean not that there is more, but that it can be ignored
if at the end of a series of commas.

Something like:

Hello <- c(
"hi",
"shalom".
... )

Might then allow extension by adding a line before the ..., or perhaps even
be set so any line with a ... is ignored. But this might take careful
consideration. For example, when the interpreter reads in lines, it should
not keep extra entries containing the "..." and you may need to check this
does not break other things as my choice of ... is a valid symbol used
elsewhere. Perhaps `%...%` or some unique symbol might serve the purpose, as
it is just syntactic sugar.

But, on the scale of things, this is not a must.

-----Original Message-----
From: R-devel <r-devel-bounces using r-project.org> On Behalf Of Manfred Kooistra
Sent: Friday, April 24, 2026 5:09 AM
To: r-devel using r-project.org
Subject: [Rd] Feature request: Allow comma after last element in a list

I've always been irritated that R doesn't allow a comma after the last
element in a "list":

> a <- c(
+     1,
+     2,
+     3
+ )
> a
[1] 1 2 3
> b <- c(
+     1,
+     2,
+     3,
+ )
Error in c(1, 2, 3, ) : argument 4 is empty

This makes updating lists unnecessarily cumbersome, which I find I
frequently do, either when I test code and want to run it with lists of
varying elements or varying orders of elements or when I maintain lists
manually over time and have to add or delete elements from them.

Is there a reason for this behavior in R and might it not be a good idea to
change it?
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