matrix() can't handle NaN (PR#193)

So just which one do
you mean?  And what are you going to achieve by having essentially a
second NA, except to blur the real purposes of NaNs?

Well to me NA means missing value, and it is abuse of NA to use it to
represent things like 0/0.

NA+NaN     

NaN+NA

NaN+NaN

is.nan(NaN)

is.nan(NA)

is.na(NaN)

The purpose of having NaN to me:
I am allowed to get an NaN as a result of some operation in R. Let's say I
then save that in a file, then I read the file in again using read.table.
In the process of saving and reading it in I lose the NaN. I don't like
that. It doesn't seem consistent. If the NaN is to be changed, I would
like to do the changing explicitly myself, so I know what happened to it.

I would also include Inf and -Inf here. These are allowed outputs from R
operations, so why can't they be read in by read.table? So I am proposing
that allowable IEEE entities Inf, -Inf, NaN be read in by read.table as
themselves (not as character strings).

PS: I remember reading on this list about complex numbers in R. That
brings in a conflict with IEEE (doesn't it?), because in IEEE,
sqrt(negative number)->NaN.
But that is not a NaN if you allow complex numbers (I would think).

sqrt(-1)

Warning: NaNs produced in function "sqrt"
[1] NaN

Is there a need for an "I" symbol in R?

sqrt(-1+0i)

sqrt(as.complex(-1))