Editing Scope (computer science) (section)

=== R ===
[[R (programming language)|R]] is a lexically scoped language, unlike other implementations of [[S (programming language)|S]] where the values of free variables are determined by a set of global variables, while in R they are determined by the context in which the function was created.<ref>{{cite web|url=https://cran.r-project.org/doc/FAQ/R-FAQ.html#Lexical-scoping|title=R FAQ|website=cran.r-project.org|access-date=19 March 2018}}</ref> The scope contexts may be accessed using a variety of features (such as <code>parent.frame()</code>) which can simulate the experience of dynamic scope should the programmer desire.

There is no block scope:
<syntaxhighlight lang="r">
a <- 1
{
  a <- 2
}
message(a)
## 2
</syntaxhighlight>

Functions have access to scope they were created in:
<syntaxhighlight lang="r">
a <- 1
f <- function() {
  message(a)
}
f()
## 1
</syntaxhighlight>

Variables created or modified within a function stay there:
<syntaxhighlight lang="r">
a <- 1
f <- function() {
  message(a)
  a <- 2
  message(a)
}
f()
## 1
## 2
message(a)
## 1
</syntaxhighlight>

Variables created or modified within a function stay there unless assignment to enclosing scope is explicitly requested:
<syntaxhighlight lang="r">
a <- 1
f <- function() {
  message(a)
  a <<- 2
  message(a)
}
f()
## 1
## 2
message(a)
## 2
</syntaxhighlight>

Although R has lexical scope by default, function scopes can be changed:
<syntaxhighlight lang="r">
a <- 1
f <- function() {
  message(a)
}
my_env <- new.env()
my_env$a <- 2
f()
## 1
environment(f) <- my_env
f()
## 2
</syntaxhighlight>