> On 27 Mar 2016, at 22:05 , Mick Jordan <mick.jor...@oracle.com> wrote:
>
> As I understand
> https://stat.ethz.ch/R-manual/R-devel/library/base/html/sys.parent.html
> sys.function(n) returns the function associated with stack frame n.
> Since frame 0 is defined as .GlobalEnv which is not associated with a
> function, I would expect this to always return NULL. However, it does not:
>
>> sys.function()
> NULL
>> f <- function(x) sys.function(x)
>> f(0)
> function(x) sys.function(x)
>> f(1)
> function(x) sys.function(x)
>> f(2)
> Error in sys.function(x) : not that many frames on the stack
>
> Why the different behavior when sys.function(0) is called inside another
> function?
This is a documentation bug. The case "which = 0" differs between sys.frame()
and sys.call()/sys.function(). For the latter, it means the current
call/function, whereas sys.frame(0) is always the global envir. It is pretty
clear from the underlying C code that the three functions treat their argument
differently:
R_sysframe has
if (n == 0)
return(R_GlobalEnv);
if (n > 0)
n = framedepth(cptr) - n;
else
n = -n;
whereas the other two (R_syscall and R_sysfunction) omit the special treatment
for n==0. Without this, n==0, comes out unchanged from the if-construct,
indicating that one should go 0 frames up the stack (same as
n==framedepth(cptr)).
Obviously, it won't work to document the "which" argument identically for all
three functions...
-pd
>
> Mick Jordan
>
>
> [[alternative HTML version deleted]]
>
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--
Peter Dalgaard, Professor,
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
Phone: (+45)38153501
Office: A 4.23
Email: pd....@cbs.dk Priv: pda...@gmail.com
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