Another example of the use of a closure in Scala.

HelloGoodbye.scala

package com.eonsahead

  object HelloGoodbye extends App {

    def greetingMaker (): () => String = {
      // This is a function that returns a function
      // to its caller.

      // This function ("greetingMaker") has one local
      // variable (named "arriving").
      var arriving = true

      // The definition of "greetingMaker" contains
      // the definition of another function ("greeting").
      // This is the function that "greetingMaker" will
      // return to its caller.
      def greeting (): String = {
        // This function ("greeting") lies within the
        // scope of the variable "arriving" that we defined
        // in the "greetingMaker" function.

        // Let the value of "arriving" determine how
        // we will greet our friend this time: "Hello"
        // or "Goodbye" ?
        val result = if( arriving ) "Hello" else "Goodbye"

        // Remember whether we were coming or going
        // the last time we greeted our friend.
        arriving = !arriving

        // Return the string "Hello" or "Goodbye"
        // as appropriate.
        result
      } // end of greeting()
      greeting
    } // end of greetingMaker

    // Create a function and store it in
    // a variable.
    val fun = greetingMaker()

    for( n <- 0 until 8) {
      // Repeatedly call the function that we created.
      // The successive calls return "Hello"
      // and "Goodbye" alternately.
      // The function has a memory!
      println( fun() )
    }

  } // HelloGoodbye