Non-local variable

In Lua they are called the upvalues of the function.

Examples

Nested functions

In the Python 3 example that follows there is a nested function inner defined in the scope of another function outer. The variable x is local to outer, but non-local to inner (nor is it global):

<span id="mwHw"></span><span class="kn" id="mwIA">from</span><span class="w" id="mwIQ"> </span><span class="nn" id="mwIg">typing</span><span class="w" id="mwIw"> </span><span class="kn" id="mwJA">import</span> <span class="n" id="mwJQ">Callable</span> <span class="k" id="mwJg">def</span><span class="w" id="mwJw"> </span><span class="nf" id="mwKA">outer</span><span class="p" id="mwKQ">()</span> <span class="o" id="mwKg">-></span> <span class="n" id="mwKw">Callable</span><span class="p" id="mwLA">[[],</span> <span class="kc" id="mwLQ">None</span><span class="p" id="mwLg">]:</span> <span class="n" id="mwLw">x</span><span class="p" id="mwMA">:</span> <span class="nb" id="mwMQ">int</span> <span class="o" id="mwMg">=</span> <span class="mi" id="mwMw">1</span> <span class="k" id="mwNA">def</span><span class="w" id="mwNQ"> </span><span class="nf" id="mwNg">inner</span><span class="p" id="mwNw">()</span> <span class="o" id="mwOA">-></span> <span class="kc" id="mwOQ">None</span><span class="p" id="mwOg">:</span> <span class="k" id="mwOw">nonlocal</span> <span class="n" id="mwPA">x</span> <span class="n" id="mwPQ">x</span> <span class="o" id="mwPg">+=</span> <span class="mi" id="mwPw">1</span> <span class="nb" id="mwQA">print</span><span class="p" id="mwQQ">(</span><span class="n" id="mwQg">x</span><span class="p" id="mwQw">)</span> <span class="k" id="mwRA">return</span> <span class="n" id="mwRQ">inner</span>

In JavaScript, the locality of a variable is determined by the closest var statement for this variable. In the following example, x is local to outer as it contains a var x statement, while inner doesn't. Therefore, x is non-local to inner:

<span id="mwTw"></span><span class="kd" id="mwUA">function</span><span class="w" id="mwUQ"> </span><span class="nx" id="mwUg">outer</span><span class="p" id="mwUw">()</span><span class="w" id="mwVA"> </span><span class="p" id="mwVQ">{</span> <span class="w" id="mwVg"> </span><span class="kd" id="mwVw">var</span><span class="w" id="mwWA"> </span><span class="nx" id="mwWQ">x</span><span class="w" id="mwWg"> </span><span class="o" id="mwWw">=</span><span class="w" id="mwXA"> </span><span class="mf" id="mwXQ">1</span><span class="p" id="mwXg">;</span> <span class="w" id="mwXw"> </span><span class="kd" id="mwYA">function</span><span class="w" id="mwYQ"> </span><span class="nx" id="mwYg">inner</span><span class="p" id="mwYw">()</span><span class="w" id="mwZA"> </span><span class="p" id="mwZQ">{</span> <span class="w" id="mwZg"> </span><span class="nx" id="mwZw">x</span><span class="w" id="mwaA"> </span><span class="o" id="mwaQ">+=</span><span class="w" id="mwag"> </span><span class="mf" id="mwaw">1</span><span class="p" id="mwbA">;</span> <span class="w" id="mwbQ"> </span><span class="nx" id="mwbg">console</span><span class="p" id="mwbw">.</span><span class="nx" id="mwcA">log</span><span class="p" id="mwcQ">(</span><span class="nx" id="mwcg">x</span><span class="p" id="mwcw">);</span> <span class="w" id="mwdA"> </span><span class="p" id="mwdQ">}</span> <span class="w" id="mwdg"> </span><span class="k" id="mwdw">return</span><span class="w" id="mweA"> </span><span class="nx" id="mweQ">inner</span><span class="p" id="mweg">;</span> <span class="p" id="mwew">}</span>

Anonymous functions

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

<span id="mwgg"></span><span class="nf" id="mwgw">outer</span><span class="w" id="mwhA"> </span><span class="ow" id="mwhQ">=</span><span class="w" id="mwhg"> </span><span class="kr" id="mwhw">let</span><span class="w" id="mwiA"> </span><span class="n" id="mwiQ">c</span><span class="w" id="mwig"> </span><span class="ow" id="mwiw">=</span><span class="w" id="mwjA"> </span><span class="mi" id="mwjQ">1</span><span class="w" id="mwjg"> </span><span class="kr" id="mwjw">in</span><span class="w" id="mwkA"> </span><span class="n" id="mwkQ">map</span><span class="w" id="mwkg"> </span><span class="p" id="mwkw">(</span><span class="nf" id="mwlA">\</span><span class="n" id="mwlQ">x</span><span class="w" id="mwlg"> </span><span class="ow" id="mwlw">-></span><span class="w" id="mwmA"> </span><span class="n" id="mwmQ">x</span><span class="w" id="mwmg"> </span><span class="o" id="mwmw">+</span><span class="w" id="mwnA"> </span><span class="n" id="mwnQ">c</span><span class="p" id="mwng">)</span><span class="w" id="mwnw"> </span><span class="p" id="mwoA">[</span><span class="mi" id="mwoQ">1</span><span class="p" id="mwog">,</span><span class="w" id="mwow"> </span><span class="mi" id="mwpA">2</span><span class="p" id="mwpQ">,</span><span class="w" id="mwpg"> </span><span class="mi" id="mwpw">3</span><span class="p" id="mwqA">,</span><span class="w" id="mwqQ"> </span><span class="mi" id="mwqg">4</span><span class="p" id="mwqw">,</span><span class="w" id="mwrA"> </span><span class="mi" id="mwrQ">5</span><span class="p" id="mwrg">]</span>