Scala: type annotations make tail recursion check fail

Question

I\'m adding type annotations to this pattern match just for my own understanding.

@annotation.tailrec def run[A](io: IO[A]): A = {
  io match {
    case Return(a         


        

Answer 1

Bonus answer: There are a lot of questions about type erasure, take a look at How do I get around type erasure on Scala? Or, why can't I get the type parameter of my collections? You can write something like

    case FlatMap(y: IO[A], g: gType@unchecked) if g.isInstanceOf[gType] =>