in src/main/scala/com/twitter/stitch/Stitch.scala [1841:1854]
override def simplify(pending: Pending): Stitch[T] =
state.get match {
case null =>
// let `pending` handle the recursion
pending.recursive(this)
case Recursive.Evaluating =>
// another run loop is already evaluating
// this recursion, let it finish
this
case s: Stitch[T] =>
// recursion is already evaluated,
// proceed with regular simplification
s.simplify(pending)
}