[Rd] R windows crash (PR#9426)

[P.Dalgaard at biostat.ku.dk]

Prof Brian Ripley wrote:
> On Thu, 21 Dec 2006, Peter Dalgaard wrote:
>
> [...]
>
>   
>> This seems reproducible on  Linux, except that it goes into an infinite
>> loop. The lm call seems to be the real culprit:
>>
>>     
>>> testfun <- function(aa=aa) return(aa)
>>> testfun()
>>>       
>> Error in testfun() : recursive default argument reference
>>     
>>> testfun <- function(aa=aa) lm(x~y,data=aa)
>>> testfun()
>>>       
>> (*poof*)
>>     
>
> The difference is in argument evaluation between closures and internal 
> functions (c() in my example, return() in yours).
>   
Er? I'd rather say that the issue is in the semantics of missing():

> f <- function(x) missing(x)
> testfun <- function(aa=aa) f(aa)
> testfun()
Error: segfault from C stack overflow

which is a bit nasty. AFAICS the thing is that the logic for detection
of recursive arguments works by forcing promises (if you at some point
need the result of the same promise you are forcing, you know that
something is wrong), but missing() tries hard not to force promises. We
already have the following anomaly,

> g <- function(v) missing(v)
> f <- function(v) g(v)
> f()
[1] TRUE
> f <- function(v=!h, h=!v) g(v)
> f()
[1] FALSE
> f <- function(v=!h, h) g(v)
> f()
[1] FALSE

so the fix could be to realize that we cannot detect missingness in a
perfectly reliable way and just pretend that arguments are always
non-missing when they have a default.

[r-bugs reinserted as cc:]

-- 
   O__  ---- Peter Dalgaard             Øster Farimagsgade 5, Entr.B
  c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K
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~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)                  FAX: (+45) 35327907