gistfile1.txt

19:07 ~/Projects/Kepler_typemacros/sandbox (topic/typemacros)$ scalac Macros.scala
19:07 ~/Projects/Kepler_typemacros/sandbox (topic/typemacros)$ scala -cp .
Welcome to Scala version 2.10.1-20121120-175733-b60f5bcf2c (Java HotSpot(TM) 64-Bit Server VM, Java 1.6.0_37).
Type in expressions to have them evaluated.
Type :help for more information.

scala> class C extends AnyRef with Macros.Foo[Int]("2")
defined class C

scala> new C().hello
res0: String = I've been created from Macros.Foo$macro[Int]("2")

scala> 19:10 ~/Projects/Kepler_typemacros/sandbox (topic/typemacros)$ cat Macros.scala 
import scala.reflect.macros.Context
import language.experimental.macros

object Macros {
  def impl[T: c.WeakTypeTag](c: Context)(x: c.Expr[Any]): c.Tree = {
    import c.universe._
    val key = "SomeUniqueName.scala"
    if (!c.enclosingRun.existsSynthetic(key)) {
      val msg = "I've been created from " + c.macroApplication
      val synthetic = reify{ trait SomeUniqueName { def hello = c.literal(msg).splice } }.tree
      c.enclosingRun.compileSynthetic(key, synthetic)
    }
    Ident(newTypeName("SomeUniqueName"))
  }

  type Foo(x: Int) = macro impl[String]
  type Foo[T](x: String) = macro impl[T]
}19:10 ~/Projects/Kepler_typemacros/sandbox (topic/typemacros)$