Meta-Programming with Scala: Loop Unrolling

package michid.meta

import michid.meta.Naturals._

object PreProc {
  def LOOP[N] = null.asInstanceOf[N]

  trait Loop[N] {
    def apply(block: => Unit)
  }

  implicit def loop0(n: ZERO) = new Loop[ZERO] {
    def apply(block: => Unit) { }
  }

  implicit def loop[N <: NAT](n: SUCC[N])(implicit f: N => Loop[N]) = new Loop[SUCC[N]] {
    def apply(block: => Unit) {
      block
      null.asInstanceOf[N].apply(block)
    }
  }

}

object LoopUnroll {
  import PreProc._

  def unrollTest() {
    // Need -Yrecursion 1
    //LOOP[(_3 x _2)#v] {
    LOOP[_5] {
      println("hello world")
    }
  }

  def main(args: Array[String]) {
    unrollTest()
  }
}

package michid.meta

object Naturals {
  trait NAT {
    type a[s[_ <: NAT] <: NAT, z <: NAT] <: NAT
    type v = a[SUCC, ZERO]
  }
  final class ZERO extends NAT {
    type a[s[_ <: NAT] <: NAT, z <: NAT] = z
  }
  final class SUCC[n <: NAT] extends NAT {
    type a[s[_ <: NAT] <: NAT, z <: NAT] = s[n#a[s, z]]
  }
  type _0 = ZERO
  type _1 = SUCC[_0]
  type _2 = SUCC[_1]
  type _3 = SUCC[_2]
  type _4 = SUCC[_3]
  type _5 = SUCC[_4]
  type _6 = SUCC[_5]

  trait ADD[n <: NAT, m <: NAT] extends NAT {
    type a[s[_ <: NAT] <: NAT, z <: NAT] = n#a[s, m#a[s, z]]
  }
  trait MUL[n <: NAT, m <: NAT] extends NAT {
    trait curry[n[_[_], _], s[_]] { type f[z] = n[s, z] }
    type a[s[_ <: NAT] <: NAT, z <: NAT] = n#a[curry[m#a, s]#f, z]
  }

  type +[n <: NAT, m <: NAT] = ADD[n, m]
  type x[n <: NAT, m <: NAT] = MUL[n, m]
}