On 22/10/2015 2:44 PM, david.kaeth...@gmail.com wrote:
Hi,
I’m sure there’s a ton I don’t understand about environments, but I’m
afraid your answer doesn’t make sense to me.
If it’s on the search path, the „print(env)“ should yield something like:
You never get to the search list.
<environment: package:pryr>
attr(,"name")
[1] "package:pryr"
attr(,"path")
[1] "/Library/Frameworks/R.framework/Versions/3.2/Resources/library/pryr“
I agree that there would only be an address if it was an unnamed
environment such as the ones constructed during function execution.
But I’m walking the search path here, so these should all contain
information on packages.
My question wasn’t so much about how to retrieve information on
environments, there are plenty functions concerning that. I just don’t
understand why it makes that much of a difference if I put the
parent.frame() in the arguments list, or in the function body.
You seem to have ignored my explanation.
Duncan Murdoch
Am 22.10.2015 um 19:05 schrieb Duncan Murdoch
<murdoch.dun...@gmail.com <mailto:murdoch.dun...@gmail.com>>:
On 22/10/2015 10:20 AM,david.kaeth...@gmail.com
<mailto:david.kaeth...@gmail.com>wrote:
Hello,
I’m trying to solve an exercise, where I want to walk through the
search path recursively
(http://adv-r.had.co.nz/Environments.html<http://adv-r.had.co.nz/Environments.html>).
I’m puzzled by a certain behavior and hope somebody can give me an
explanation.
This code works:
listenv <- function(env = parent.frame()) {
if (identical(env, emptyenv())) {
#stop("reached emptyenv", call. = FALSE)
return(env)
} else {
print(env)
listenv(parent.env(env))
}
}
Here, the calling environment is determined with a default parameter
in the function’s formals.
However, if I want to assign the calling environment within the
function’s body, I get the error message „infinite recursion“. Also,
I never get actual environments (with attributes, that is), only
memory addresses like this: <environment: 0x10da46630>.
I'm not sure what you were looking for, but "<environment: 0x10da46630>"
is the normal way to print an environment, unless it happens to be one
of the special named ones (like .GlobalEnv).
listenv <- function(env) {
env <- parent.frame()
if (identical(env, emptyenv())) {
#stop("reached emptyenv", call. = FALSE)
return(env)
} else {
print(env)
listenv(parent.env(env))
}
}
Any explanation of what’s going on here would be greatly
appreciated. I suspect it has to do with when exactly the
parent.frame()-expression is evaluated, but that’s not an actual
explanation.
Your function completely ignores the "env" argument. It never recurses.
In the first case, "parent.frame()" is only a default value, so
recursion happens properly. If you change the first line in the body to
these two lines
if (missing(env))
env <- parent.frame()
it would be equivalent.
Duncan Murdoch
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