When/how/where is parent.frame in a default argument interpreted?

environment, r

Solution

Default arguments are evaluated within the evaluation frame of the function call, from which place `parent.frame()` is the calling environment. `envir`'s value will thus be a pointer to the environment from which `fn` was called.

Also, just try it out to see for yourself:

debug(fn)
fn()
# debugging in: fn()
# debug at #2: {
# }
Browse[2]> envir
# <environment: R_GlobalEnv>

Problem

Truth be told, I'm just being lazy here, but perhaps someone could someday profit from the answer being here. Say I define a function like: ``` fn<-function(envir=parent.frame()) { #do something with envir } ``` My question is: what might I expect to be the content of envir? Context: I had a rather long function f1 that contained a call to parent.frame. Now, I want to extract part of that function (containing the parent.frame call) into a new helper function f2 (which will then be called by f1), and I want to be sure that f1 does the same as it did before.

Original source