[R] how to access an executing environment?

[Spencer Graves]

On 5/29/2014 7:40 AM, Greg Snow wrote:
> I believe that what is happening is that you never run fun1, so no
> environment for fun1 is ever created and therefore x1 is never defined
> with its own environment.  You grab the statement y <- x1 from the
> body of fun1, but then tries to evaluate it in the current environment
> (where it cannot find x1).
>
> The reason you cannot find the executing environment for fun1 is
> because it is never created.


       Of course.  Thanks.
>
> Maybe if you tell us more about what you are trying to accomplish we
> can give better suggestions for how to approach it.


       I'm trying to create a system for animation to generate a series 
of plots from a function that creates one plot.  The current status of 
this effort is "animate" in "Ecfun" available on R-Forge 
[install.packages("Ecdat", repos="http://R-Forge.R-project.org") or "svn 
checkout svn://r-forge.r-project.org/svnroot/ecdat/"].


        Since my earlier question, I fixed that problem with " funList 
<- as.list(fun)" and then passing funList to eval.  Other problems 
remained with "op <- par(mar=c(2,2,2,1)); on.exit(par(op)); plot(1)":  
First, "op" did not get assigned where it could be found.  When I wrote 
code to do assignments manually, "on.exit" was executed before "plot".  
See below.  I can work around this also, but I hope this isn't followed 
by yet another problem like this.


       Suggestions?
       Thanks,
       Spencer


fun3 <- function(fun){
   funList <- as.list(fun)
   bo <- body(fun)
   nbo <- length(bo)
   for(ib in seq(2, length=nbo-1)){
     bi <- bo[[ib]]
     print(objects())
     print(par('mar'))
     if(as.character(bi[[1]])=="<-"){
       if(length(bi)==3){
         assign(as.character(bi[[2]]),
              eval(bi[[3]], funList) )
         next
       } else {
         warning('Possible eval problem in ',
                 as.character(bi))
       }
     }
     eval(bi, funList)
   }
   print(objects())
}

funPar <- function(y1=1, y2=2){
   op <-par(mar=c(2,2,2,1))
   on.exit(par(op))
   plot(y1)
}
fun3(funPar)
[1] "bi"      "bo"      "fun"     "funList" "ib"      "nbo"
[1] 5.1 4.1 4.1 2.1
[1] "bi"      "bo"      "fun"     "funList" "ib"      "nbo" "op"
[1] 2 2 2 1
[1] "bi"      "bo"      "fun"     "funList" "ib"      "nbo" "op"
[1] 5.1 4.1 4.1 2.1
[1] "bi"      "bo"      "fun"     "funList" "ib"      "nbo" "op"

> On Wed, May 28, 2014 at 6:29 PM, Spencer Graves
> <spencer.graves at structuremonitoring.com> wrote:
>> Hello:
>>
>>
>>        I'm writing code to modify a function, and I want to know how to
>> access the executing environment of the function.  The example below
>> extracts the body of a function and executes a single line but can't find
>> "x1" in the function's executing environment.  How would you suggest fixing
>> this?  Thanks, Spencer
>>
>>
>> fun1 <- function(x1=1){
>>    y <- x1
>> }
>> fun2 <- function(fun=fun1){
>>    bo <- body(fun)
>>    bo2 <- bo[[2]]
>>    z <- eval(bo2)
>> }
>> tst <- fun2()
>>
>> Error in eval(expr, envir, enclos) : object 'x1' not found
>>>
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