[R] on lexical scoping....

[Duncan Murdoch]

You can't change the basic way R searches, but you can ask for a 
different kind of search.  For example, to see if "x" exists, you can use

  exists("x")

and it will do the default search, but

  exists("x", inherits = FALSE)

will only look in the current environment.  The get() function has a 
similar argument which returns the value

Unfortunately these functions have overly complicated argument lists 
because they are based on functions in S from 30-40 years ago, and it 
had very different scoping rules.  My advice would be to ignore the 
"where" and "frame" arguments, and always use "envir" if you want to say 
where to look.

Duncan Murdoch

On 04/04/2023 10:28 a.m., akshay kulkarni wrote:
> Dear Deepayan,
>                                THanks for the pithy, pointed reply.
> 
> But isn't it risky? Can I somehow get a warning when x is not defined in the global environment but takes on a value from one of the loaded packages? any packages for that?
> 
> THanking you,
> Yours sincerely,
> AKSHAY M KULKARNI
> ________________________________
> From: Deepayan Sarkar <deepayan.sarkar using gmail.com>
> Sent: Tuesday, April 4, 2023 7:51 PM
> To: akshay kulkarni <akshay_e4 using hotmail.com>
> Cc: R help Mailing list <r-help using r-project.org>
> Subject: Re: [R] on lexical scoping....
> 
> 
> 
> On Tue, Apr 4, 2023 at 7:26 PM akshay kulkarni <akshay_e4 using hotmail.com<mailto: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.
> 
> That is not the correct interpretation of the error. R will happily evaluate
> 
> y   <-   pi*10
> 
> even if the global environment does not contain pi. The "environments" where R will look is given by
> 
> search()
> 
> If you manage to find a package that defines 'x' (and exports it), attaching it will put the package on the search path, and then your call will indeed no longer give an error.
> 
> -Deepayan
> 
> 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
> 
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> 
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> 
> ______________________________________________
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