[Rd] R windows crash (PR#9426)

[ripley at stats.ox.ac.uk]

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.


On Thu, 21 Dec 2006, robert.denham at nrm.qld.gov.au wrote:

> 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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