[R] function doesn't exists but still runs..... (akshay kulkarni)
Jeff Newmiller
jdnewm|| @end|ng |rom dcn@d@v|@@c@@u@
Fri Jan 20 18:59:40 CET 2023
This is not a "problem" ... it is a "feature". Packages often use functions from other packages, but that does NOT mean that you as a user can automatically use those functions also.
If Package A uses Package B to implement something, but Package B becomes unavailable, the maintainer of Package A would like to fill in the gap. If Package A "Depends" on Package B then users of package A automatically get access to Package B and they get used to treating Package A like it contains all of the functions in Package B directly.
Therefore it is common to have Package A "Import" Package B so that the Package A maintainer won't have to re-implement all of Package B to avoid breaking code for users of Package A. They can fix things under the hood for their own Package A functions using other code.
If a user wants to depend on Package B, it is up to them to use the library function to do so explicitly... and when Package B goes away, they are responsible for dealing with that mess themselves.
You asked "how", and got answers... but you didn't bother to follow up on those answers by reading things like "Writing R Extensions" or Hadley Wickham's "R Packages" or "Advanced R". Don't turn that laziness into a value judgement about "problems" with R.
On January 20, 2023 9:18:54 AM PST, akshay kulkarni <akshay_e4 using hotmail.com> wrote:
>Dear Jorgen,
> thanks for the reply.....so according to you one can pegion hole the problem as concerning R's lexical scoping rules,am I right? Or some arcane concept regarding environments....?
>
>THanking you,
>Yours sincerely,
>AKSHAY M KULKARNI
>________________________________
>From: Jorgen Harmse <JHarmse using roku.com>
>Sent: Friday, January 20, 2023 9:34 PM
>To: r-help using r-project.org <r-help using r-project.org>; akshay_e4 using hotmail.com <akshay_e4 using hotmail.com>; williamwdunlap using gmail.com <williamwdunlap using gmail.com>
>Subject: Re: function doesn't exists but still runs..... (akshay kulkarni)
>
>
>It may help to expand a bit on Bill Dunlap's answer. I think that library does something like this:
>
>
>
>Create a new environment for all the package objects. This environment will not be directly visible from .GlobalEnv, and ancestor environments may not be directly visible either. It may contain functions & other objects that are not exported, and it may use objects in ancestor environments that .GlobalEnv doesn't see directly. On the other hand, functions in the package will still see external functions in the way the package author intended instead of seeing functions with the same name that are visible to .GlobalEnv.
>
>
>
>Run the source code in the private environment (using source(local=private environment, ....)?). Most package source code just defines functions, but the source code could build other objects that the package needs for some reason, or it could use delayedAssign to build the objects lazily. By default, the environment of any function defined by the source code is the private environment, so the function has access to private objects and to anything in ancestor environments.
>
>
>
>Create a second new environment whose parent is parent.env(.GlobalEnv). For every export, assign the corresponding object from the private environment into the corresponding name in the public environment. Note that the environment of any function is still the private environment in which it was created. (I think that a function is mostly determined by its environment, its formals, and its body. A function call creates a new environment whose parent is the environment of the function. Thus whoever wrote the function can control the search for anything that isn�t passed in or created by the function itself.)
>
>
>
>Reset parent.env(.GlobalEnv) to be the public environment. This makes all the exported objects (usually functions) available at the command line and allows the user to see everything that was available before (usually by name only, but by scope-resolved name if necessary). As noted by Bill Dunlap and in more detail above, package functions can use functions & other objects that are not directly visible to the user. As he also showed, you can (usually) pierce the privacy as long at least one function is exported. environment(package_function) is the private environment, so you can use it to see all the private objects and everything in the ancestor environments. You can repeat the trick to see private environments of packages you didn't directly pull in. I think you can even unlock bindings and do ghastly things to the package's private environment.
>
>
>
>Regards,
>
>Jorgen Harmse.
>
>------------------------------
>
>Message: 17
>Date: Thu, 19 Jan 2023 16:02:31 -0800
>From: Bill Dunlap <williamwdunlap using gmail.com>
>To: akshay kulkarni <akshay_e4 using hotmail.com>
>Cc: R help Mailing list <r-help using r-project.org>
>Subject: Re: [R] function doesn't exists but still runs.....
>Message-ID:
> <CAHqSRuTCBqh84FHg7=Xmd9qHxUiAN3Y4zBJbkAR3dRWhggu89Q using mail.gmail.com>
>Content-Type: text/plain; charset="utf-8"
>
>Look into R's scoping rules. E.g.,
>https://bookdown.org/rdpeng/rprogdatascience/scoping-rules-of-r.html.
>
>* When a function looks up a name, it looks it up in the environment in
>which the function was defined.
>* Functions in a package are generally defined in the package's environment
>(although sometimes they are in a descendent of the parent's environment).
>* When one searches an environment for a name, if it is not found in the
>environment the search continues in the parent environment of that
>environment, recursively until the parent environment is the empty
>environment.
>
>> with(environment(wdman::selenium), java_check)
>function ()
>{
> javapath <- Sys.which("java")
> if (identical(unname(javapath), "")) {
> stop("PATH to JAVA not found. Please check JAVA is installed.")
> }
> javapath
>}
><bytecode: 0x000001fd0ab826a8>
><environment: namespace:wdman>
>
>-Bill
>
>On Thu, Jan 19, 2023 at 2:28 PM akshay kulkarni <akshay_e4 using hotmail.com>
>wrote:
>
>> dear members,
>> I am using the RSelenium package which uses
>> the function selenium() from the wdman package. The selenium function
>> contains the function java_check at line 12. If I try to run it, it throws
>> an error:
>>
>> > javapath <- java_check()
>> Error in java_check() : could not find function "java_check"
>>
>> Also:
>>
>> > exists("java_check")
>> [1] FALSE
>>
>> But when I run selenium(), it works fine....
>>
>> How do you explain this conundrum? You can refer to this link:
>> https://github.com/ropensci/wdman/issues/15
>>
>> Specifically what concept of R explains this weird behaviour?
>>
>> 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]]
>
>
>
>
>------------------------------
>
>Subject: Digest Footer
>
>_______________________________________________
>R-help using r-project.org mailing list
>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.
>
>
>------------------------------
>
>End of R-help Digest, Vol 239, Issue 20
>***************************************
>
> [[alternative HTML version deleted]]
>
--
Sent from my phone. Please excuse my brevity.
More information about the R-help
mailing list