Test_2.scala:9: error: macro implementation not found: foo (the most common reason for that is that you cannot use macro implementations in the same compilation run that defines them)

println(foo(42))

^

one error found

-language:experimental.macros

import scala.reflect.macros.{Context => Ctx}

trait Impls {

def impl(c: Ctx)(x: c.Expr[Any]) = x

}

import scala.reflect.macros.{Context => Ctx}

object Macros extends Impls {

def foo(x: Any) = macro impl

}

object Test extends App {

import Macros._

println(foo(42))

}