protected function extractInterpolation($list)
{
$items = $list[2];
foreach ($items as $i => $item) {
if ($item[0] == "interpolate") {
$before = array("list", $list[1], array_slice($items, 0, $i));
$after = array("list", $list[1], array_slice($items, $i + 1));
return array("interpolated", $item, $before, $after);
}
}
return $list;
}