lying about return type (scala macros). compiler infers the type of generated code. sweet. as a bonus you can crash the compiler if you mix in some singleton types

Awesome.scala

import reflect.macros.Context
import language.experimental.macros

def producerImpl[A: c.WeakTypeTag](c: Context): c.Expr[Any] = {
  c.universe.reify{
    () => (??? : A)
  }
}

def producer[A] = macro producerImpl[A]

/*
scala> producer[Int]
res0: () => Int = <function0>
*/

Broken.scala

import reflect.macros.Context
import language.experimental.macros

class Box[+A]

object Box {
  def apply[A <: AnyRef](a: A) = new Box[a.type]
}

object Main {
  def iffImpl(c: Context): c.Expr[Any] = {
    import c.universe._
    val a = c.literal("a")
    reify{ Box("a") }
  }

  def iff = macro iffImpl
}