public function __construct(Collector $collector, FunctionValue $wrapper)
{
C::guardHasArity($wrapper, 2);
if ($collector->isNullaryCollector()) {
throw new Exception("It makes no sense to wrap around a nullary collector.");
}
$this->_collector = $collector;
$this->_wrapper = $wrapper;
}
public static function combineCollectors(Collector $l, Collector $r)
{
$l_empty = $l->isNullaryCollector();
$r_empty = $r->isNullaryCollector();
if ($l_empty && $r_empty) {
return new NullaryCollector();
} elseif ($r_empty) {
return $l;
} elseif ($l_empty) {
return $r;
} else {
return new ApplyCollector($l, $r);
}
}