Understanding environments and frames

envs.R

# What you need to know:
#  * environments -- inheritance of definition
#  * frames -- call reference
#
# What does that mean?
#   * environments are inherited when a function is defined (i.e. f <- function () {})
#   * frames refer to where a function was called from, not where it was defined

i <- 1

# This demonstrates environment inheritance
f1 <- function (x) {
    print(exists("i"))
    print(parent.env(environment()))
    j <- 2
    function (y) {
        print(exists("j"))
        print(parent.env(environment()))
        k <- 3
            function (z) {
                print(exists("k"))
                print(parent.env(environment()))
                ls()
            }
    }
}

f2 <- f1(10)
f3 <- f2(100)

# This demonstrates the call stack
f1 <- function (x) {
    print(exists("i"))
    print(sys.parent()) # <-- 0
    (function() {print(sys.parent())})()  # <-- 1
    j <- 2
    function (y) {
        print(exists("j"))
        print(sys.parent(2)) # <-- 0
        k <- 3
            function (z) {
                print(exists("k"))
                print(sys.parent(3)) # <-- 0
                ls()
            }
    }
}

f2 <- f1(10)
f3 <- f2(100)