1: <?php
 2: 
 3: namespace Alchemy\util\promise;
 4: 
 5: 
 6: /**
 7:  * Signals are Waitables with the concept of a 'source', a dynamic value
 8:  * represented by a callable that returns either an unresolved NULL, an
 9:  * Exception, or a non-NULL value.
10:  */
11: class Signal extends Waitable {
12:     protected $fnSource = null;
13: 
14: 
15:     public function __construct($source = null, $type = null) {
16:         parent::__construct($type);
17: 
18:         if (is_callable($source)) {
19:             $this->fnSource = $source;
20:         } else {
21:             $this->resolve($source);
22:         }
23:     }
24: 
25: 
26:     /**
27:      * Queries the Signal's source for its current value. If this is
28:      * itself a Waitable, that Waitable becomes the new source.
29:      */
30:     protected function precheck() {
31:         if ($this->fnSource !== null) {
32:             $this->resolve(call_user_func($this->fnSource));
33:         }
34: 
35:         if ($this->result instanceof Waitable) {
36:             $this->fnSource = $this->result;
37:             $this->result = null;
38:             $this->check();
39:         }
40:     }
41: }