Hanoi towers at compile time become very easy with dependent types. https://gist.github.com/travisbrown/3772462

gistfile1.scala

> shapeless-core/console
[warn] Credentials file /home/folone/.ivy2/.credentials does not exist
[info] Compiling 24 Scala sources to /home/folone/workspace/shapeless/core/target/scala-2.11/classes...
[info] Starting scala interpreter...
[info] 
Welcome to Scala version 2.11.0-20130205-141957-132e09fc2e (OpenJDK 64-Bit Server VM, Java 1.7.0_09).
Type in expressions to have them evaluated.
Type :help for more information.

scala> import shapeless.SingletonTypes._
import shapeless.SingletonTypes._

scala> :paste
// Entering paste mode (ctrl-D to finish)

def hanoi(n: Int, a: String = "A", b: String = "B", c: String = "C"): String = {
  if (n == 0) ""
  else {
    hanoi(n-1, a, c, b) + "from " + a + " to " + b + "; " + hanoi(n-1, c, b, a)
  }
}

// Exiting paste mode, now interpreting.

hanoi: (n: Int, a: String, b: String, c: String)String

scala> implicitly[^(hanoi(3))]
<console>:12: error: could not find implicit value for parameter e: String("from A to B; from A to C; from B to C; from A to B; from C to A; from C to B; from A to B; ")
              implicitly[^(hanoi(3))]
                        ^