[Rd] sys.on.exit not working (PR#7665)

[p.dalgaard at biostat.ku.dk]

Prof Brian Ripley <ripley at stats.ox.ac.uk> writes:

> It is working as documented: there is no on.exit set for str, is there?
> 
>       'sys.on.exit()' retrieves the expression stored for use by
>       'on.exit' in the function currently being evaluated. (Note that
>                                 ^^^^^^^^^^^^^^^^^^^^^^^^^
>       this differs from S, which returns a list of expressions for the
>       current frame and its parents.)
> 
> I see you have looked at PR#269, but did not notice the crucial
> difference: here the current function is str (it is evaluating its
> arguments), not soe.test.
> 
> On Mon, 7 Feb 2005 mark.bravington at csiro.au wrote:
> 
> > Full_Name: Mark Bravington
> > Version: 2.0.1
> > OS: Windows XP
> > Submission from: (NULL) (140.79.22.104)
> >
> >
> > 'sys.on.exit()' doesn't seem to be working, since R1.7.1 at least:
> 
> Please read the FAQ: we don't want R-bugs clogged up with `doesn't
> seem to be working' reports, and we do say so.
> 
> > soe.test <- function() {
> >  on.exit( cat( 'In exit code\n'))
> >  str( sys.on.exit()) # should display "language..." I think
> >  12
> > }
> >
> > (A similar bug was apparently fixed for version 0.65!)
> 
> One difference being that PR#269 was a bug, and this is not.

It does, however, point to a subtlety with the sys.xxx functions,
which is liable to confuse users to the point of submitting spurious
bug reports. Perhaps we should add a note to the help page (in the
vain hope that people will read it).

Notice, BTW, that this exposes a slightly anomalous handling of the
"<-" operator. AFAIK this is common to all .Primitive calls, as
opposed to .Internal and other function calls: They do not create a
new context, hence do not increase sys.nframe() and sys.whatever in
the arguments still refer to the callers frame.

> soe.test
function() {
  on.exit( cat( 'In exit code\n'))
  a <- sys.on.exit() ; str(a)
  12
 }

> soe.test()
 language cat("In exit code\n")
In exit code
[1] 12

but if you replace "<-" with a corresponding call to assign(), then
you get.

> soe.test()
 NULL
In exit code
[1] 12

-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)             FAX: (+45) 35327907