How to "instantiate" an enviroment in the current one?

Question

Suppose that the function

foo

returns its enviroment, like this:

foo <- function () {

  a <- 42

  b <- "a string"

  x <- FALSE

  environment()

}

...and that function

bar

invokes

foo

like this:

bar <- function () {

  a <- 0

  z <- pi



  cat("before\n")

  print(ls.str())



  INSTANTIATE(foo())



  cat("after\n")

  print(ls.str())

}

...where

INSTANTIATE

is a placeholder for an as-yet undefined function (or construct).

The hypothetical expression

INSTANTIATE(foo())

is intended as shorthand for the directive

instantiate the environment returned by
foo()
in the current enviroment.

By "instantiate" I mean that all the variables mentioned in

foo()

get created (if necessary) in the current enviroment, and assigned to values they have in

foo()

.

This means that the desired output for

bar()

is the following:

> bar()

before

a :  num 0

z :  num 3.14

after

a :  num 42

b :  chr "a string"

x :  logi FALSE

z :  num 3.14

My question is, what should I replace the expression

INSTANTIATE(foo())

such that the output of

bar()

looks like I've shown above?

EDIT: Please assume that

foo

should remain unchanged.

EDIT: This implementation of

INSTANTIATE(foo())

, inspired by Gregor's comment (or, rather, my interpretation thereof), does not work:

bar <- function () {

  a <- 0

  z <- pi

  cat("before\n")

  print(ls.str())



  list2env(as.list(foo()))



  cat("after\n")

  print(ls.str())

}



> bar()

before

a :  num 0

z :  num 3.14

after

a :  num 0

z :  num 3.14

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Answer 1

How about something like this

import_env <- function(env, to=parent.frame()) {
    vars <- ls(envir=env)
    for(v in vars) {
        assign(v, get(v, env),to)
    }
}

Tested with

foo <- function () {
  a <- 42
  b <- "a string"
  x <- FALSE
  environment()
}

bar <- function () {
  a <- 0
  z <- pi

  cat("before\n")
  print(ls.str())

  import_env(foo())

  cat("after\n")
  print(ls.str())
}

bar()
# before
# a :  num 0
# z :  num 3.14
# after
# a :  num 42
# b :  chr "a string"
# x :  logi FALSE
# z :  num 3.14

Basically we just iterate the environment and assign all the variables over. This should work for atomic types. Things get a bit trickier if you ever tried to copy over functions or formulas which hold on to the environment where they were created.

How to "instantiate" an enviroment in the current one?

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