example of currying

curry.scala

// you have items
case class Item(name: String, price: Double)

// their prices can be adjusted.  To adjust a price, pass a function
// which takes the old price, and gives a new price
def adjustPrice(i: Item, discountFunction: Double => Double) = {
  // return a new copy with the price changed
  i.copy(price = discountFunction(i.price))
}

def absoluteDiscount(amount: Double)(oldPrice: Double) = oldPrice - amount
def fractionalDiscount(percent: Double)(oldPrice: Double) = oldPrice * percent
def setNewPrice(newPrice: Double)(oldPrice: Double) = newPrice
def setToZero(oldPrice: Double) = 0

val items = List(Item("one hundred", 100d),
                 Item("fifty", 50d))

val discounted10 = items.map { item => adjustPrice(item, absoluteDiscount(10d)) }
val fiftyPercent = items.map { item => adjustPrice(item, fractionalDiscount(.5)) }
val all20 = items.map { item => adjustPrice(item, setNewPrice(20)) }
val everythingIsFree = items.map { item => adjustPrice(item, setToZero) }

println( discounted10)
println( fiftyPercent)
println( all20)
println( everythingIsFree)


// curry the adjust price function so that it retuns a new function
// which modifies a particular item

val groovy = Item("groovy", 1000)
val adjustGroovy : (Double => Double) => Item = adjustPrice(groovy, _)

println(adjustGroovy(absoluteDiscount(10)))
println(adjustGroovy(fractionalDiscount(.30)))