R function which returns a function... and variable scope

Question

I am learning about functions returning other functions. For example:

foo1 <- function()
{
  bar1 <- function()
  {
    return(constant)
  }
}

foo2 <- function()
{
  constant <- 1
  bar2 <- function()
  {
    return(constant)
  }
}

Suppose, now, I declare functions f1 and f2 as follows:

constant <- 2
f1 <- foo1()
f2 <- foo2()

Then it appears they have the same function definition:

> f1
function()
  {
    return(constant)
  }
<environment: 0x408f048>
> f2
function()
  {
    return(constant)
  }
<environment: 0x4046d78>
> 

BUT the two functions are different. For example:

> constant <- 2
> f1()
[1] 2
> f2()
[1] 1

My question: Why is it legal for two functions, with identical function definitions, to produce different results?

I understand that foo1 treats constant as a global variable and foo2 as a constant variable, but it is impossible to tell this from the function definition surely?

(I am probably missing something fundamental.)

Answer 1

Sure they're different, the environments are different. Try ls(environment(f1)) and then ls(environment(f2)) and then get('constant', environment (f1)) and same for f2