build.sbt

scalaVersion := "2.9.1"

libraryDependencies ++= Seq(
  "org.scalaz" %% "scalaz-core" % "6.0.3"
)

initialCommands in console := "import scalaz._;import Scalaz._"

scalacOptions ++= Seq(
  "-deprecation"
)

Main.scala

package scalaz_memo_example

import scala.util.control.Exception.allCatch
import scalaz._
import Scalaz._

object Main{

  def timer[T](f : => T):T = { 
    val start = System.currentTimeMillis
    val r = f 
    println("\n" + (System.currentTimeMillis - start))
    r   
  }
 
  val ZERO = BigInt(0)
  val ONE  = BigInt(1)

  def fib(n:Int):BigInt = { 
    require(n >= 0)

    def f(x:BigInt):BigInt = x match {
      case ZERO => x
      case ONE  => x    
      case _    => f(x-1) + f(x-2)
    }   

    f(n)
  }

  val bigIntMemo = arrayMemo[BigInt](100) 
  val memorizedFib = bigIntMemo(fib)

  def main(args:Array[String]){
    val n = allCatch.opt{args.head.toInt}.getOrElse(35)
    timer{ print( memorizedFib(n) ) } 
    timer{ print( memorizedFib(n) ) } 
    timer{ print( memorizedFib(n) ) } 
  }
}

output

[info] Running scalaz_memo_example.Main 
9227465
3814
9227465
0
9227465
0
[success] Total time: 15 s, completed Oct 22, 2011 2:12:15 PM