Scala Conditional Compilation

ConditionalCompilation.scala

import scala.language.higherKinds

object Conditions {
  //based on: An Introduction to Functional Programming Through Lambda Calculus
  trait BOOL {
    type body[e1 <: E, e2 <: E, E] <: E //select: (E, E) => E
  }
  trait TRUE extends BOOL {
    type body[e1 <: E, e2 <: E, E] = e1 //true = select_first
  }
  trait FALSE extends BOOL {
    type body[e1 <: E, e2 <: E, E] = e2 //false = select_second
  }
  trait COND[e1 <: E, e2 <: E, E, c <: BOOL] {
    type r = c#body[e1, e2, E] //cond = λe1.λe2.λc.((c e1) e2)
  }

  //let E = BOOL, IF[c, e1, e2] just return TRUE or FALSE
  //type IF[c <: BOOL, e1 <: BOOL, e2 <: BOOL] = COND[e1, e2, BOOL, TRUE]#r
  //implicitly[IF[TRUE, FALSE, TRUE] =:= TRUE]

  //not = λx.(((cond false) true) x)
  type NOT[x <: BOOL] = COND[FALSE, TRUE, BOOL, x]#r
  //and = λx.λy.(((cond y) false) x)
  type AND[x <: BOOL, y <: BOOL] = COND[y, FALSE, BOOL, x]#r
  //or = λx.λy.(((cond true) y) x)
  type OR[x <: BOOL, y <: BOOL] = COND[TRUE, y, BOOL, x]#r

  type ![x <: BOOL] = NOT[x]
  type ||[x <: BOOL, y <: BOOL] = OR[x, y]
  type &&[x <: BOOL, y <: BOOL] = AND[x, y]
  //test
  implicitly[ TRUE && FALSE || NOT[FALSE] =:= TRUE]
}

object CondCompilation {
  //based on blog: https://michid.wordpress.com/2008/10/29/meta-programming-with-scala-conditional-compilation-and-loop-unrolling/
  import Conditions._
  def _IF[B] = null.asInstanceOf[B]

  //TRUE => Include
  object Include {
    def apply(block: => Unit) {
      block
    }
  }
  //FALSE => Exclude
  object Exclude {
    def apply(block: => Unit) { }
  }

  implicit def include(t: TRUE) = Include
  implicit def exclude(f: FALSE) = Exclude
}

object IfDefTest {
  import Conditions._
  import CondCompilation._

  type LOG = TRUE
  type ERR = TRUE
  type WARN = FALSE
  type DEV = TRUE

  def errTest() {
    _IF[LOG && ERR] {
      println("err")
    }
  }

  def warnTest() {
    _IF[LOG && WARN] {
      println("warn")
    }
  }

  def main(args: Array[String]) {
    errTest()
    warnTest()

    _IF[DEV] {
      println("dev")
    }
  }
}