unary !

Martin Maechler writes:

[spill over from  R-core]

"TL" == Thomas Lumley <thomas@biostat.washington.edu> writes:

Another thing I noticed when playing with chron is that apparently
code like if (!(length(value)) works in S but not in R.  The error
in R is unary ! is only defined for logical vectors

I assume that this is a bug and not a feature (although the code in
src/main/logic.c makes me wonder ...).

TL> I complained about this more than a year ago and I thought we (or
TL> in those days R+R) had decided it was a feature -- I just explained
TL> to someone on r-help that it was one of the deliberate
TL> incompatibilities that ! didn't work on numerics.

Yes, positively.  We've discussed this quite a bit, and
this was defined to be a feature long ago.

The proper (non C-hacker but normal-user readable) way is to test for

	if(length(vector) == 0)

O.k.  I will add this to the FAQ but I am still not convinced.  If I may
e.g. do

R> 0 & 0
[1] FALSE
R> 1 | 0
[1] TRUE

then why can't !0 be TRUE?

-k
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