R windows crash (PR#9426)

On Thu, 21 Dec 2006, P.Dalgaard at biostat.ku.dk wrote:

  

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.
    

We could also mark the promise created for default arguments so it can
be identified as such and use that info in missing().  Probably worth
deciding what the intended semantics are here and then figuring out
the implementation.

  

f <- function(v=h,h=v) g(v)
f()

f <- function(v=(v)) g(v)
f()