def makeCounter(): String => Int = { 
  var c = 0; 
  {op => {
    if (op equals "up") c = c + 1 
    else if (op equals "down") c = c -1
    else if ( !(op equals "show")) error("unknown op for counter: " + op)
    c
  }
 }
}


def makeCounter1(): String => Int = { 
  var c = 0; 
  def make(op: String): Int = {
    if (op equals "up") c = c + 1 
    else if (op equals "down") c = c -1
    else if ( !(op equals "show")) error("unknown op for counter: " + op)
    c
  }
  make
}

//
// Closure: function + plus access to surrounding definitions (environment)
//
// Closures are objects and objects are closures
//

def makeCounter2(): String => Int = { 
  var c = 0; 
  def incr = { c += 1 ; c }
  def decr = { c -= 1 ; c }
  def show = { c }
  {op => {
    if (op equals "up") incr
    else if (op equals "down") decr
    else if (op equals "show") show
    else error("unknown op for counter: " + op)
  }
 }
}