in src/main/scala/com/twitter/stitch/Stitch.scala [1882:1899]
override def simplify(pending: Pending): Stitch[U] = {
if (result != null) return result
input = input.simplify(pending)
input match {
case Const(t) =>
result = a.run(t, locals).simplify(pending)
result
case Transform(s, l, b) if l == locals =>
this.input = s.asInstanceOf[Stitch[T]]
this.a = b
.andThenNoReassoc(a)
.asInstanceOf[Arrow[T, U]] // suppress ide warning
this
case _ =>
this
}
}