Non-local variable

In programming language theory, a non-local variable is a variable that is not defined in the local scope. While the term can refer to global variables, it is primarily used in the context of nested and anonymous functions where can some variable can be neither in the local nor in the global scope.

Example

In the example that follows there is a nested function inner defined in the scope of another function outer. The variable is local to outer, but non-local to inner (nor is it global):

def outer():
    x = 1
    def inner():
        nonlocal x
        x += 1
        print(x)
    return inner

In this example the variable c is non-local in the anonymous function \x -> x + c:

outer = let c = 1 in map (\x -> x + c) [1, 2, 3, 4, 5]

Example

See also