[R] on lexical scoping....

[Duncan Murdoch]

It seems mostly correct. Here are a few quibbles:

- I don't think "owner" is a good description of the parent environment. 
  Usually when I use owner in computing, there's an implication that the 
owner controls what it owns, is responsible for allocating and 
destroying it, etc.  Parent environments are targets of a pointer from 
other environments that list them as their "enclosure", but they have no 
record of their children.

- The analogy that all roads lead to the search list is wrong.  There's 
no reason you couldn't create an environment whose parent was the empty 
environment.  But with the qualifier "when we start in R_GlobalEnv" it's 
correct, so this complaint is just about the wording.

- The description of what Imports does is wrong.  What is described 
there is what the `import()` directive in NAMESPACE does.  The Imports 
line in DESCRIPTION just guarantees that the named package is loaded, it 
doesn't import anything.  And the `importFrom()` directive in NAMESPACE 
isn't discussed.

- It gets bad near the end in the "Curveball" section.  I'd just skip 
that.  It's not at all true that all functions in a package have the 
package's namespace environment as their environment.  There are lots of 
real examples where that's not true.  Functions that maintain persistent 
records (e.g. the base function conflictRules()) often have a private 
environment, and occasionally packages import functions from other 
packages by simple assignment, so they end up in the namespace 
environment of the importer but still have the namespace environment of 
the exporter associated with them.  And the last diagram (the revised 
one with all solid lines) is just misleading.

Duncan

On 04/04/2023 7:53 p.m., Mark Leeds wrote:
> obviously, everyone has different opinions on what's useful but I always
> found this document quite
> helpful. I think, in the past, someone said that there are some incorrect
> statements in but I'm not sure
> what they are.
> 
> https://askming.github.io/study_notes/Stats_Comp/Note-How%20R%20searches%20and%20finds%20stuff.html
> 
> 
> On Tue, Apr 4, 2023 at 7:06 PM Bert Gunter <bgunter.4567 using gmail.com> wrote:
> 
>> The following *might* be of use to you. If you can predict what the various
>> function invocations will do, I think you have a reasonable grasp of how
>> lexical scoping works in R (contrary or supplementary opinions welcome).
>> It is the sort of thing you will find in the references also. If this is
>> all obvious, sorry for wasting your time.
>> #######################
>> search()
>> ls()
>> dat <- list(x =2)
>> attach(dat,2)
>> search()
>> f <- function(){
>>     g <- function() x
>>     x <- 3
>>     g}
>> h <- f()
>> g <- function()x
>> ls()
>> h()
>> g()
>> detach(dat)
>> h()
>> g()
>>
>> ##########################
>> ## Here is what this gives starting with an empty .GlobalEnv.
>> ##################################
>>
>>> search()
>>   [1] ".GlobalEnv"        "package:tools"     "package:lattice"
>> "tools:rstudio"
>>   [5] "package:stats"     "package:graphics"  "package:grDevices"
>> "package:utils"
>>   [9] "package:datasets"  "package:methods"   "Autoloads"
>> "package:base"
>>> ls()
>> character(0)
>>> dat <- list(x =2)
>>> attach(dat,2)
>>> search()
>>   [1] ".GlobalEnv"        "dat"               "package:tools"
>> "package:lattice"
>>   [5] "tools:rstudio"     "package:stats"     "package:graphics"
>>   "package:grDevices"
>>   [9] "package:utils"     "package:datasets"  "package:methods"
>> "Autoloads"
>> [13] "package:base"
>>> f <- function(){
>> +    g <- function() x
>> +    x <- 3
>> +    g}
>>> h <- f()
>>> g <- function()x
>>> ls()
>> [1] "dat" "f"   "g"   "h"
>>> h()
>> [1] 3
>>> g()
>> [1] 2
>>> detach(dat)
>>> h()
>> [1] 3
>>> g()
>> Error in g() : object 'x' not found
>>
>> -- Bert
>>
>>
>> On Tue, Apr 4, 2023 at 6:56 AM akshay kulkarni <akshay_e4 using hotmail.com>
>> wrote:
>>
>>> Dear Members,
>>>                               I have the following code typed at the
>>> console prompt:
>>>
>>> y   <-   x*10
>>>
>>> X has not been defined and the above code throws an object not found
>>> error. That is, the global environment does not contain x. Why doesn't it
>>> look further in the environment stack, like that of packages? There are
>>> thousands of packages that contain the variable named  x. Of course, that
>>> happens if the above code is in a function (or does it?).
>>>
>>> What concept of R is at work in this dichotomy?
>>>
>>> THanking you,
>>> Yours sincerely,
>>> AKSHAY M KULKARNI
>>>
>>>          [[alternative HTML version deleted]]
>>>
>>> ______________________________________________
>>> R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see
>>> https://stat.ethz.ch/mailman/listinfo/r-help
>>> PLEASE do read the posting guide
>>> http://www.R-project.org/posting-guide.html
>>> and provide commented, minimal, self-contained, reproducible code.
>>>
>>
>>          [[alternative HTML version deleted]]
>>
>> ______________________________________________
>> R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide
>> http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>>
> 
> 	[[alternative HTML version deleted]]
> 
> ______________________________________________
> R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.