declare

The declare statement is used to temporarily change the state of the parser in a block of code. Here's how it looks:

function tick()
{
    static $i;
    printf("[tick i=%d]\n", ++$i);
}

register_tick_function("tick");

declare (ticks = 2) {
    1; 2; 3;
}

Ticks is well suited for implementing simple multitasking, backgrounded IO and many other things in PHP.

See also register_tick_function() and unregister_tick_function().