1 files changed, 86 insertions, 0 deletions
diff --git a/test/files/presentation/callcc-interpreter/src/CallccInterpreter.scala b/test/files/presentation/callcc-interpreter/src/CallccInterpreter.scala
new file mode 100644
index 0000000000..ce3b996b96
--- /dev/null
+++ b/test/files/presentation/callcc-interpreter/src/CallccInterpreter.scala
@@ -0,0 +1,86 @@
+object callccInterpreter {
+
+  type Answer = Value
+
+  /**
+   * A continuation monad.
+   */
+  case class M[A](in: (A => Answer) => Answer) {
+    def bind[B](k: A => M[B])          = M[B](c => in (a => k(a) in c))
+    def map[B](f: A => B): M[B]        = bind(x => unitM(f(x)))
+    def flatMap[B](f: A => M[B]): M[B] = bind(f)
+  }
+
+  def unitM[A](a: A) /*?*/ = M[A](c => c(a))
+
+  def id[A] /*?*/ = (x: A) => x
+  def showM(m: M[Value]) /*?*/ = (m in id).toString()
+
+  def callCC[A](h: (A => M[A]) => M[A]) =
+    M[A](c => h(a => M[A](d => c(a))) in c)
+
+  type Name = String
+
+  trait Term
+  case class Var(x: Name) extends Term
+  case class Con(n: int) extends Term
+  case class Add(l: Term, r: Term) extends Term
+  case class Lam(x: Name, body: Term) extends Term
+  case class App(fun: Term, arg: Term) extends Term
+  case class Ccc(x: Name, t: Term) extends Term
+
+  trait Value
+  case object Wrong extends Value {
+   override def toString() = "wrong"
+  }
+  case class Num(n: Int) extends Value {
+    override def toString() = n.toString()
+  }
+  case class Fun(f: Value => M[Value]) extends Value {
+    override def toString() = "<function>"
+  }
+
+  type Environment = List[Pair[Name, Value]]
+
+  def lookup(x: Name, e: Environment): M[Value] = e match {
+    case List() => unitM(Wrong)
+    case Pair(y, b) :: e1 => if (x == y) unitM(b) else lookup(x, e1)
+  }
+
+  def add(a: Value, b: Value) /*?*/ = Pair(a, b) match {
+    case Pair(Num(m), Num(n)) => this./*!*/unitM(Num(m + n))
+    case _ => unitM(Wrong)
+  }
+
+  def apply(a: Value, b: Value): M[Value] = a match {
+    case Fun(k) => k(b)
+    case _ => unitM(Wrong)
+  }
+
+  def interp(t: Term, e: Environment): M[Value] = t match {
+    case Var(x) => lookup(x, e)
+    case Con(n) => unitM(Num(n))
+    case Add(l, r) => for (val a <- interp(l, e);
+			   val b <- interp(r, e);
+			   val c <- add(a, b))
+                      yield c
+    case Lam(x, t) => unitM(Fun(a => interp(t, Pair(x, a) :: e)))
+    case App(f, t) => for (val a <- interp(f, e);
+			   val b <- interp(t, e);
+			   val c <- apply(a, b))
+		      yield c
+    case Ccc(x, t) => callCC(k => interp(t, Pair(x, Fun(k)) :: e))
+  }
+
+  def test(t: Term): String = showM(interp(t, List()))
+
+  val term0 = App(Lam("x", Add(Var("x"), Var("x"))), Add(Con(10), Con(11)))
+  val term1 = App(Con(1), Con(2))
+  val term2 = Add(Con(1), Ccc("k", Add(Con(2), App(Var("k"), Con(4)))))
+
+  def main(args: Array[String]) {
+    println(test(term0))
+    println(test(term1))
+    println(test(term2))
+  }
+}
+\ No newline at end of file