examples of currying and a closure

Higher.scala

import java.io.PrintWriter
import scala.io.Source

object Higher extends App {
  println("Sputnik!")

  // Here's an example of a closure.
  // f is a function that returns a
  // function to its caller
  // the function g that it returns
  // knows about the variable count
  // that is declared in f
  // call to g remembers what was done
  // in the n-th call
  def f():(Char) => Char = {
    var count = 0
    def g(c:Char):Char = {
      count += 1
      if( count % 5 == 0) '*' else c
    } // g(Char)
    g
  } // f()

  //  I put a short text file in a folder that I named
  // "resources" in the src/main folder of my project
  val path = getClass.getResource( "poem.txt")
  println( path )

  var poem = Source.fromFile( path.getFile, "UTF-8")
  val verses = poem.getLines()
  for( line <- verses )
    println( line )

  println( "\nDone with verses!\n")

  poem = Source.fromFile( path.getFile, "UTF-8")
  val letters = poem.iter.filter( {_.isLetter} ).map( {_.toUpper } )

  // Here's an example of "currying a function"

  val offset = 3
  // First, define a function with 2 parameters (a Char and an Int)
  // that returns a Char to its caller
  val caesar:(Char, Int) => Char =
    (letter, offset) => (((letter - 'A') + offset) % 26 + 'A').toChar

  // Second, use that function to define a
  // second function with 1 Int parameter that
  // returns a function with Char parameter
  val myCaesar: (Int) => (Char) => Char =
    (offset:Int) => caesar(_, offset )

  // assign to shifter a function that
  // has 1 Char argument and returns a
  // Char to its caller
  val shifter = myCaesar(3)
  // apply that function to each character
  // in a sequence of characters
  val shifted = letters.map( shifter )

  // next, put all characters into one big string
  // while replacing each character using f,
  // the function that we defined with a closure
  val y = shifted.foldLeft("") ((a:String,b:Char) => a + b).map( f )

  println( y )
  //for( c <- shifted )
  //  println( c )

  println( "\nDone with letters!\n" )

} // Higher