gistfile1.txt

import scala.reflect.macros.{BlackboxContext, WhiteboxContext}
import scala.annotation.compileTimeOnly
import scala.language.experimental.macros

object Macros {
  def impl(c: WhiteboxContext)(body: c.Tree) = {
    import c.universe._
    val Block(stats0, expr) = body
    val stats: List[Tree] = stats0 :+ expr
    def yyTransform(stats: List[Tree]): List[List[Tree]] = {
      object Yret {
        def unapply(stat: Tree): Option[Tree] = {
          // println(stat)
          // println(showRaw(stat))
          stat match {
            case q"Macros.yret($x)" => Some(x)
            case _ => None
          }
        }
      }
      // println(stats)
      // println(Yret.unapply(stats.head))
      val (prefix, suffix) = (stats.span(s => Yret.unapply(s).isEmpty))
      // println(prefix, suffix)
      suffix match {
        case Yret(x) :: rest => List(prefix :+ x) ++ yyTransform(rest)
        case Nil => List(prefix)
      }
    }
    val transformed = yyTransform(stats) match {
      case init :+ Nil => init
      case xs => xs
    }
    // println(transformed)
    val thunks = transformed.map(stats => q"() => { ..$stats }")
    // println(thunks)
    q"List(..$thunks).iterator.map(thunk => thunk())"
  }

  def yy[T](body: T): Any = macro impl

  @compileTimeOnly("can't use yret outside yy")
  def yret(x: Any): Unit = ???
}

===========

import Macros._

object Test extends App {
  val x = yy {
    println("returning 2")
    yret(2)
    println("returning 3")
    yret(3)
  }
  println("hello")
  println(x.toList)
}

===========

Если заменить сигнатуру `def yret(x: Any): Unit` на `def yret[T](x: T): Unit`, то получается проблема с КЦ. Ни `q"Macros.yret[Int]($x)"`, ни `q"Macros.yret[$_]($x)"` не будут матчить вызовы yret.