# What is "..." when it's empty? -- differences to S

**Peter Dalgaard BSA
**
p.dalgaard@biostat.ku.dk

*26 Jun 1999 16:53:02 +0200*

Martin Maechler <maechler@stat.math.ethz.ch> writes:
>* 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.
*>*
*>* 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 don't have S-plus 5.0r3 around, but the two others are consistent
with the result of length(), resp. mode() (with no arguments), both of
which have minor R/S incompatiblities. I see nothing wrong with "...",
but we might consider modifying length() and mode(), both of which
look like one-line if(is.missing(.... changes.
--
O__ ---- Peter Dalgaard Blegdamsvej 3
c/ /'_ --- Dept. of Biostatistics 2200 Cph. N
(*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard@biostat.ku.dk) FAX: (+45) 35327907
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