Created
February 19, 2009 13:51
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Scala-Metaprogramming: Towers of Hanoi
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/* | |
* This is the Towers of Hanoi example from the prolog tutorial [1] | |
* converted into Scala, using implicits to unfold the algorithm at | |
* compile-time. | |
* | |
* [1] http://www.csupomona.edu/~jrfisher/www/prolog_tutorial/2_3.html | |
*/ | |
object TowersOfHanoi { | |
import scala.reflect.Manifest | |
def simpleName(m:Manifest[_]):String = { | |
val name = m.toString | |
name.substring(name.lastIndexOf('$')+1) | |
} | |
trait Nat | |
final class _0 extends Nat | |
final class Succ[Pre<:Nat] extends Nat | |
type _1 = Succ[_0] | |
type _2 = Succ[_1] | |
type _3 = Succ[_2] | |
type _4 = Succ[_3] | |
case class Move[N<:Nat,A,B,C]() | |
implicit def move0[A,B,C](implicit a:Manifest[A],b:Manifest[B]):Move[_0,A,B,C] = { | |
System.out.println("Move from "+simpleName(a)+" to "+simpleName(b));null | |
} | |
implicit def moveN[P<:Nat,A,B,C](implicit m1:Move[P,A,C,B],m2:Move[_0,A,B,C],m3:Move[P,C,B,A]) | |
:Move[Succ[P],A,B,C] = null | |
def run[N<:Nat,A,B,C](implicit m:Move[N,A,B,C]) = null | |
case class Left() | |
case class Center() | |
case class Right() | |
def main(args:Array[String]){ | |
run[_2,Left,Right,Center] | |
} | |
} |
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Using shapeless I created a version which moves the result to the type.
It obviously ruins the 'self-contained'ness of the gist, but here it is: https://gist.github.com/HusrevAtSky/cae020c79c844e22024c8cd027a5c6ce