R windows crash (PR#9426)

The problem is rather that 'aa' *is* found: default arguments are looked 
for within the body of the function, and so the calculation of 'aa' is 
recursive.  Consider the simpler case
testfun <- function(aa=aa) {aa <- c(aa); aa}
testfun()
Error in testfun() : recursive default argument reference

On Linux I got
testfun() #R then exits.
Error: segfault from C stack overflow

Now C stack overflows are instantly fatal on Windows and cannot be caught 
there.  However, using Linux enabled me to locate the loop in a debugger, 
and it is recursion in isMissing to which I have added a stack check.

The remedy is I hope obvious: 'don't do that'.

Adding these checks do have a small but measurable performance cost so we 
have been conservative in adding them.

Full_Name: Robert Denham
Version: R-2.4.1
OS: Windows Xp
Submission from: (NULL) (61.88.57.1)

R gui exits without warning when I run a function which has an argument with a
default that is not found.

This was a result of an error in a function I wrote, but I thought that it
should exit more gracefully than it does. Here is an example:

testfun <- function(aa=aa) {
   aa <- lm(y~x,data=aa)
   return(aa)
}

testfun() #R then exits.

Note that

testfun <- function(aa=bb) {
   aa <- lm(y~x,data=aa)
   return(aa)
}

works as it should, giving "object bb not found".

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Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
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Oxford OX1 3TG, UK                Fax:  +44 1865 272595