Closure Because of What it Can Do or Because it Does

Question

Ok, this is a bit of a pedantic question but I\'d like to make sure I\'m understanding the definition correctly. Is the closure moniker used to describe anonymous functions that

Answer 1

One great definition of a closure is defined here: lua.org

When a function is written enclosed in another function, it has full access to local variables from the enclosing function; this feature is called lexical scoping. Although that may sound obvious, it is not. Lexical scoping, plus first-class functions, is a powerful concept in a programming language, but few languages support that concept.

Answer 2

Assuming you mean within the context of computer science...

A closure is a first class function which captures the lexical bindings of free variables in its defining environment. Once it has captured the lexical bindings the function becomes a closure because it "closes over" those variables.

Note this means closures only exist at run time.

For a function to be a closure is orthogonal to the function being anonymous or named. You can create a language that allows you to define named functions to be closures.

Here is a "named" closure in Python:

def maker():
  count=[0]
  def counter():
    count[0]=count[0]+1
    return count[0]
  return counter