Question

How can I query the value of x for foo in the R code below?

make.foo <- function() {
    x <- 123
    function() x * 3
}

foo <- make.foo()

# now get foo's x

Answer 1

A function will have an environment

from ?`function`

A closure has three components, its formals (its argument list), its body (expr in the ‘Usage’ section) and its environment which provides the enclosure of the evaluation frame when the closure is used.

so you can get from that environment (or list the objects using ls)

get('x', envir = environment(foo))
## [1] 123

or if you want to know all the objects in the environment

ls(envir = environment(foo))
## 'x'

and if you want to assign to that environment (ie change x)

assign('x', 24, envir = environment(foo))

foo()
## 72

You can even remove it from the environment

rm(x, envir = environment(foo))
foo()
## Error in foo() : object 'x' not found

and then use a globally assigned x

x <- 3
foo()
# [1] 9

and reassign to the function‘s environment

assign('x', 123, envir = environment(foo))
foo()
## [1] 369