PrimeNumbers.scala

/**
 *            DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE
 *                    Version 2, December 2004
 * 
 * Copyright (C) 2013 Lukáš Karas <lukas.karas@centrum.cz>
 * 
 * Everyone is permitted to copy and distribute verbatim or modified
 * copies of this license document, and changing it is allowed as long
 * as the name is changed.
 * 
 *             DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE
 *   TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
 * 
 *  0. You just DO WHAT THE FUCK YOU WANT TO.
 */

/**
 * This is a small useless example that prints prime numbers less that 1000, written in Scala.
 * 
 *    scalac PrimeNumbers.scala  && java -classpath .:scala-library-2.9.2.jar PrimeNumbers
 */
object PrimeNumbers {

  def primeTest(x: Stream[Int], y: Int): Boolean= {
    if (x.isEmpty) {
      true
    } else {
      //println(y + "%" + x.head )
      if (y % x.head == 0) {
        false
      }
      else {
        primeTest(x.tail, y)
      }
    }
  }

  def isPrime2(i:Int ): Boolean = {
    //println("is " + i + " prime?")
	if (i!=2 && i%2==0)
		false
	else
		primeTest((3 to (Math.sqrt(i).toInt) by 2).toStream, i)
  }


  def isPrime(i: Int): Boolean = {
    if (i <= 3) {
      true
    } else {

      if (i % 2 == 0) {
        //println(i + " je sude cislo")
        false
      } else {
        //println(i + " NENI sude cislo")

        var sqrt = Math.sqrt(i).toInt
        var j = 3
        while (j <= sqrt) {
          if (j == sqrt)
            return true
          else if (i % j == 0)
            return false
          j += 2
        }
        true
        //throw new IllegalStateException("This should never happen")

      }
    }
  }

  def main(args: Array[String]) {

    (1 to 1000).map(i => {
      if (isPrime2(i))
        println(i)
    }
    )
  }
}