> From: r-devel-boun...@r-project.org
> [mailto:r-devel-boun...@r-project.org] On Behalf Of
> thmsfuller...@gmail.com
> Sent: Thursday, May 13, 2010 10:16 AM
> To: r-devel@r-project.org
> Subject: [Rd] What functions are called internally in R to
> resolve whatvariable is referred?
>
> Hello All,
>
> If I refer to a variable 'x', 'x' will be searched in the current
> frame or the parent frame, or the parent of the parent frame, etc.,
> until it is found (or not found at all)?
Be careful with your terms here. While a function
is evaluating its 'parent frame' is the environment
of the function that called it and its 'parent environment'
is the environment in which it was defined. R searches
though the chain of parent environments, not parent frames.
The following example shows the difference between the
parent environment and the parent frame.
# setup
x <- "Global x"
f1 <- function() {
c(x=x,
xFromParentFrame=get("x", envir=parent.frame()),
xFromParentEnv=get("x", envir=parent.env(environment())))
}
f0 <- function(i) {
x<-paste("f0's x: i=", i, sep="")
# Note how subf0 and f1 have identical definitions:
# they only differ in where they were created.
subf0 <- function ()
{
c(x = x,
xFromParentFrame = get("x", envir = parent.frame()),
xFromParentEnv = get("x", envir = parent.env(environment())))
}
list(subf0=subf0(), f1=f1(), FUN=subf0)
}
> # run the functions
> z <- f0(17)
> z
$subf0
x xFromParentFrame xFromParentEnv
"f0's x: i=17" "f0's x: i=17" "f0's x: i=17"
$f1
x xFromParentFrame xFromParentEnv
"Global x" "f0's x: i=17" "Global x"
$FUN
function ()
{
c(x = x, xFromParentFrame = get("x", envir = parent.frame()),
xFromParentEnv = get("x", envir = parent.env(environment())))
}
<environment: 0x292af70>
> z$FUN()
x xFromParentFrame xFromParentEnv
"f0's x: i=17" "Global x" "f0's x: i=17"
Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com
> Could you please show me what
> code in R source that handles this? Is it in the C code or the R code?
>
> Thanks,
> Tom
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