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>.
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.
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