What is "..." when it's empty? -- differences to S
Prof Brian D Ripley
ripley@stats.ox.ac.uk
Sun, 27 Jun 1999 08:39:51 +0100 (BST)
On Sat, 26 Jun 1999, Martin Maechler wrote:
> i) (function(x, ...) length(...))(1)
>
> gives 0 in S (plus 3.4) and an error in R.
> It also gives an error in Splus 5.0r3.
> So we could well remain as we are... however
>
> ii) (function(x, ...) length(...))(1,2)
>
> gives 1 in all dialects of S that I have available.
> So by my `continuation logic', I'd argue that "i)" above should give 0
> (and R and S-plus 5.0r3 behave inconsistently.
Try
iii) (function(x, ...) length(...))(1,2,3)
to see that the continuation logic is false.
I think function(x, ...) length(list(...)) is what one wants here, and they
(R, 3.4, 5.1) are all consistent on that. (I see that is what you put in
C.)
> Do we yet have any documentation on "..." ??
>
> In both Splus 3.4 and 5.0r3,
> (function(x, ...) mode(...))(1) returns "missing"
> whereas R gives an interesting error:
> R> trace(mode)
> R> (function(x, ...) mode(...))(1)
> trace: mode(...)
> Error: Argument "x" is missing, with no default
>
> ---
> What is desired for R?
I would leave these: none of them seem sensible uses of ... to me.
BTW, NEWS says
o C() didn't works (again?) for a single argument
which apart from grammar seems not entirely precise. It looks to me that
it failed if how.many _and_ ... were missing, and that was broken only
once, in
revision 1.2.2.1
date: 1999/05/05 01:25:24; author: ripley; state: Exp; lines: +4 -3
Add ... args to pass to contr.treatment etc
Also, I do not really like `didn't work': can we try to distinguish
between `failed' (gave an error) and `gave incorrect results'?
Reason: the second is much more serious.
Brian
--
Brian D. Ripley, ripley@stats.ox.ac.uk
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
University of Oxford, Tel: +44 1865 272861 (self)
1 South Parks Road, +44 1865 272860 (secr)
Oxford OX1 3TG, UK Fax: +44 1865 272595
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