[R-sig-Geo] R Scoping Rules

[Gabor Grothendieck]

You can use parent.frame(n), see ?parent.frame and ?get,  but its
probably not a good idea since you will wind up with a function that
does not work in the way the rest of R works.

On Sun, Apr 18, 2010 at 9:17 PM, Stephen G. Eick <eick at vistracks.com> wrote:
> Thanks.  This makes sense.  Is there any way to make R search over every
> frame all the way back to the global frame?
>
> simple <- function(env = parent.frame()) {
>   if(exists("height", env)) cat("height exists\n")
>   else cat("height does not exist\n")
> }
> a<-function()simple()
> foo <- function() { height <- 3; a() }
> foo() # height does not exist
>
> -----Original Message-----
> From: Gabor Grothendieck [mailto:ggrothendieck at gmail.com]
> Sent: Sunday, April 18, 2010 8:00 PM
> To: eick at cs.uic.edu
> Cc: r-sig-geo at stat.math.ethz.ch
> Subject: Re: [R-sig-Geo] R Scoping Rules
>
> R uses lexical scope. That means that when a variable is not found in
> a function it next looks where the function was _defined_ and not
> where the function was called from.   Since simple is defined in the
> global environment it looks there for height if can`t find it within
> simple.  The parent environment is where the function was defined and
> the parent frame is where it was called from.  To force it to look in
> the parent frame rather than the parent environment try this:
>
> simple <- function(env = parent.frame()) {
>   if(exists("height", env)) cat("height exists\n")
>   else cat("height does not exist\n")
> }
> foo <- function() { height <- 3; simple() }
> foo() # height exists
>
>
> On Sun, Apr 18, 2010 at 8:27 PM, Stephen G. Eick <eick at vistracks.com> wrote:
>> simple<-function() {
>>
>> if(exists("height"))
>>
>> cat("height exists\n")
>>
>> else
>>
>> cat("height does not exist\n")
>>
>> }
>>
>>
>>
>> foo<-function() {
>>
>> height<-10
>>
>> simple()
>>
>> }
>>
>>
>>
>>> foo()
>>
>> height does not exist
>>
>>
>>
>> Can somebody please explain why "simple" does not find the "height"
> variable
>> when I run it?
>>
>>
>>
>> Is there an easy way to make R use scoping rules like python where it
>> searches over all frames to find the value of an symbol?
>>
>>
>>
>> Thanks, Steve Eick
>>
>>
>>
>>
>>        [[alternative HTML version deleted]]
>>
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>
>