Context and CoEffects in PHP: https://github.com/facebook/hhvm/blob/master/hphp/hack/doc/HIPs/contexts_and_coeffects.md

contexts.php

<?php


/**
 * @context={}
 */
function foo(): void {}

/**
 * @context={io}
 */
function bar(): void  { echo 'bar'; }

/**
 * @context={rand}
 */
function baz(): int { return mt_rand(1, 10); }

/**
 * @context={io, rand}
 */
function qux(): void { echo baz(); }

/**
 * @template Tk of array-key
 * @template Tv
 * @template Ts
 *
 * @context-template C1
 * @context-template C2
 *
 * @param (iterable<Tk, Tv>){C1} $iterable
 * @param (callable(Tk): Ts){C2} $fun
 *
 * @return array<Tk, Ts>
 *
 * @context={...C1, ...C2}
 */
function map(iterable $iterable, callable $fun): array
{
  $r = [];
  foreach($iterable as $k => $i) { $r[$k] = $i; }
  return $r;
}

/**
 * this function is pure, so it has no effects ( {} )
 *
 * @context={}
 */
function main(): void
{
  map(
    [1, 2],
    /**
     * @context={}
     */
    static fn(int $i): int => $i + 1
  );
}