Parent issue: #335
Every plugin must be able to use all properties to construct the exact PSI element being fed in to achieve isomorphism between Quote and Scope. To ensure that AST parsing and our quote-and-template system is robust, more testing is needed to increase stability and reliability.

Checklist for WhenExpression

• Destructure and make available all methods related to re

In scalaz/scalaz#1958 @fommil uses this optimization:

fa match {
  case Right(b) => f(b)
  case Left(a) => Left(a)
}

fa match {
  case Right(b) => f(b)
  case a => a.asInstanceOf[Either[L, B]]
}

perhaps we could detect this particular case and optimize it automatically.