On 5/17/14, 4:00 PM, peter dalgaard wrote:
On 17 May 2014, at 19:42 , Mick Jordan <mick.jor...@oracle.com> wrote:
According to
:https://stat.ethz.ch/R-manual/R-devel/library/base/html/environment.html
"If |fun| is a function or a formula then |environment(fun)| returns the
environment associated with that function or formula. If |fun| is |NULL|
then the current evaluation environment is returned."
environment()
<environment: R_GlobalEnv>
environment(environment)
<environment: namespace:base>
This makes sense, however I have two questions on things that don't seem
to make sense:
1.
.Internal(environment(NULL))
<environment: base>
Since we are calling from R_GlobalEnv, how can the calling environment
be base?
Read the Description section in ?.Internal carefully....
Basically, you are calling .Internal from the command line. It is not designed
to be called from there and only wizards know what happens if it is. (The set
of wizards who might know whether it makes any sense at all does not include
me!)
Well, calling from the shell. Anyway, I was just surprised by the result
as, notwithstanding the fact that .Internal is "special", the calling
environment is definitely .globalEnv. The enclosing environment might
well be different, but that's not what environment(NULL) returns. My
curiosity relates to the fact that the two calls have different stack
depths, so that the .Internal(environment(NULL)) call has to detect
whether it was called via environment() or .Internal(environment(NULL))
in order to return the right answer.
2.
In eval.R in library/base/R:
.GlobalEnv <- environment()
parent.frame <- function(n = 1) .Internal(parent.frame(n))
etc.
Since the functions being defined are in base, how can the calling
environment be R_GlobalEnv. Or does this just set .GlobalEnv temporarily
to base?
.GlobalEnv is a variable in base alright. The assignment happens when base is
being loaded and _at that point_ the environment is R_GlobalEnv.
Sorry, I don't understand how that can be. The function definitions in,
say, eval.R, and all the others in library/base/R, end up in base, as
made clear by ls(baseenv()). So if these files are evaluated in the
"usual way", and the environment() call in eval.R returns globalenv(),
then they would, in fact, be defined there and not in baseenv. Now, I
realise that this is startup code, so perhaps the implementation does
something special and these files really aren't evaluated in the "usual"
way.
Mick
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