Dear Jorgen,
regrets to reply this late....
I got into this issue because it threw an error, and it took more than 4 days
to fix this. I learnt a lot, and one things I learnt is to debug the
function, even when that is a public package function....instead of googling
the error message...Any ideas on how to do this more efficiently?
THanking you,
Yours sincerely,
AKSHAY M KULKARNI
________________________________
From: Jorgen Harmse <jhar...@roku.com>
Sent: Friday, January 20, 2023 11:35 PM
To: akshay kulkarni <akshay...@hotmail.com>; r-help@r-project.org
<r-help@r-project.org>; williamwdun...@gmail.com <williamwdun...@gmail.com>
Subject: Re: [EXTERNAL] Re: function doesn't exists but still runs..... (akshay
kulkarni)
Hi Akshay,
Lexical scoping and environments are closely tied. (I think Bill even cited the
documentation.) I guess it's arcane in the sense that scoping usually does what
you expect, but the way that works is related to what we discussed.
What led you to discover the issue? Were you debugging the public package
function because it didn't do what you expected, or were you just curious how
it worked?
Regards,
Jorgen.
From: akshay kulkarni <akshay...@hotmail.com>
Date: Friday, January 20, 2023 at 11:19
To: Jorgen Harmse <jhar...@roku.com>, r-help@r-project.org
<r-help@r-project.org>, williamwdun...@gmail.com <williamwdun...@gmail.com>
Subject: [EXTERNAL] Re: function doesn't exists but still runs..... (akshay
kulkarni)
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 <jhar...@roku.com>
Sent: Friday, January 20, 2023 9:34 PM
To: r-help@r-project.org <r-help@r-project.org>; akshay...@hotmail.com
<akshay...@hotmail.com>; williamwdun...@gmail.com <williamwdun...@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 <williamwdun...@gmail.com>
To: akshay kulkarni <akshay...@hotmail.com>
Cc: R help Mailing list <r-help@r-project.org>
Subject: Re: [R] function doesn't exists but still runs.....
Message-ID:
<CAHqSRuTCBqh84FHg7=xmd9qhxuian3y4zbjbkar3drwhggu...@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...@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
>
>
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>
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