Understanding closures

In programming languages, a closure is a powerful concept that allows a function to capture and retain references to variables from its lexical environment (the environment where the function is defined). This means that even after the outer function has finished executing or has gone out of scope, the inner function (the closure) still retains access to the variables from its enclosing scope.

Closures are created when an inner function references variables from its containing function or any other surrounding scope. The inner function closes over those variables, hence the term closure.

The ability of a closure to maintain access to variables from its lexical environment is particularly useful in scenarios where you need to create functions with behavior that depends on the values of certain variables at the time the function was defined.

Here’s a simple example of a closure in Power Query M:

let
  x = 10,
  closureFunction = () =>...