gistfile1.txt

13:29 ~/Projects/Kepler_introduce-member/sandbox (topic/introduce-member)$ cat Macros.scala 
import scala.reflect.macros.Context
import language.experimental.macros

object Macros {
  def impl(c: Context)(target: c.Tree, name: c.Tree, code: c.Tree) = {
    import c.universe._
    val Literal(Constant(targetType: Type)) = c.typeCheck(target)
    val Literal(Constant(methodName: String)) = name
    val Function(methodParams, methodBody) = code
    val method = DefDef(NoMods, TermName(methodName), Nil, List(methodParams), TypeTree(), methodBody)
    c.introduceMember(targetType.typeSymbol, method)
    c.literalUnit
  }

  def addMethod(target: _, name: String, code: _)  = macro impl
}
13:29 ~/Projects/Kepler_introduce-member/sandbox (topic/introduce-member)$ cat Test.scala

// class C

object Test extends App {
  Macros.addMethod(classOf[C], "foo", (x: Int) => x + 2)
  println(new C().foo(2))
}

class C

13:29 ~/Projects/Kepler_introduce-member/sandbox (topic/introduce-member)$ scalac Macros.scala && scalac Test.scala && scala Test
4

cool~

Eugene, what is the scope of this new method? Does it become global?

No, the introduced member becomes the proper member of the provided owner class, trait or object.