PHPCfg\Traverser::traverseBlock PHP Method

    private function traverseBlock(Block $block, Block $prior = null)
    {
        if ($this->seen->contains($block)) {
            $this->event("skipBlock", [$block, $prior]);
            // Always return null on a skip event
            return null;
        }
        $this->seen->attach($block);
        $this->event("enterBlock", [$block, $prior]);
        $children = $block->children;
        for ($i = 0; $i < count($children); $i++) {
            $op = $children[$i];
            $this->event("enterOp", [$op, $block]);
            foreach ($op->getSubBlocks() as $subblock) {
                $sub = $op->{$subblock};
                if (!$sub) {
                    continue;
                }
                if (!is_array($sub)) {
                    $sub = [$sub];
                }
                for ($j = 0; $j < count($sub); $j++) {
                    $result = $this->traverseBlock($sub[$j], $block);
                    if ($result === Visitor::REMOVE_BLOCK) {
                        array_splice($sub, $j, 1, []);
                        // Revisit the ith block
                        $j--;
                    } elseif ($result instanceof Block) {
                        $sub[$j] = $result;
                        // Revisit the ith block again
                        $j--;
                    } elseif (!is_null($result)) {
                        throw new \RuntimeException("Unknown return from visitor: " . gettype($result));
                    }
                }
                if (is_array($op->{$subblock})) {
                    $op->{$subblock} = $sub;
                } else {
                    $op->{$subblock} = array_shift($sub);
                }
            }
            $result = $this->event("leaveOp", [$op, $block]);
            if ($result === Visitor::REMOVE_OP) {
                array_splice($children, $i, 1, []);
                // Revisit the ith node
                $i--;
            } elseif ($result instanceof Op) {
                $children[$i] = $result;
                // Revisit the ith node again
                $i--;
            } elseif (!is_null($result) && $result !== $op) {
                throw new \RuntimeException("Unknown return from visitor: " . gettype($result));
            }
        }
        $block->children = $children;
        return $this->event("leaveBlock", [$block, $prior]);
    }