Functional Programming and Domain Modelling

examples.sc

import scala.util.Try

println("Hello World")


//Functions as first class citizen

def someFunction = {a: Int=> a + 10}
val zz = someFunction


//Immutability
//val a = 10
//a= a + 20

//Composability


def squareFun = { x: Int => x * x }
val x = squareFun

def sumFunction(f: Int => Int, a: Int, b: Int): Int = {
  (a to b).map(f).sum
}

sumFunction(squareFun, 1, 10)

def sumFunctionCurried(f: Int => Int)(a: Int, b: Int): Int = {
  (a to b).map(f).sum
}

val sumSquaredFunction = sumFunctionCurried(squareFun)_

val int = sumSquaredFunction(1,10)

//Even Higher

def combineFunction(combineOp: (Int,Int)=>Int,initialValue: Int)(f: Int=>Int)(a: Int, b: Int) = {
  var result = initialValue // Oh noes?!
  for(number<- a to b) {
    result = combineOp(f(number),result)
  }
  result
}

def add = {(a: Int,b: Int)=> a + b}
def multiply = {(a: Int,b: Int)=> a*b}
def newSumFunction = combineFunction(add,0)_

def cubes= {x: Int => x * x * x}
newSumFunction(cubes)(1,3)

def prodFunction = combineFunction(multiply,1)_
prodFunction(x=>x)(1,4)


//val reserveProducts, blockPayment, isProductAvailable,hasReceivedPayment = { _: Any => true }
//
//
//trait Product {}
//
//case class Order(items: List[Product])
//
//case class Gadget(name: String) extends Product
//
//case class HouseHoldItem(name: String) extends Product
//
//trait PaymentType
//
//case class CashPayment(amount: Int) extends PaymentType
//
//case class CardPayment(amount: Int) extends PaymentType
//
//
//case class OrderSummary(products: List[Product], paymentType: PaymentType)
//
////def processPurchase: List[Product] => PaymentType => Try[OrderSummary] = ???
//
//
//
//
//val orderSummary = processPurchase(List(Gadget("Mobile")))(CashPayment(500))
//
//def processPurchase: List[Product] => PaymentType => Try[OrderSummary] = {
//  products => {
//    paymentType => {
//      Try {
//        require(isProductAvailable(products))
//        reserveProducts(products)
//        blockPayment(paymentType)
//        hasReceivedPayment(paymentType)
//        OrderSummary(products, paymentType)
//      }
//    }
//  }
//
//}
//
//
//
//
////Higher Order
//def combineFunction(combineOp: (Int,Int)=>Int,startValue: Int)(f: Int=>Int)(a: Int, b: Int) = {
//  var result = startValue // Oh noes?!
//  for(number<- a to b) {
//    result = combineOp(f(number),result)
//  }
//  result
//}
//
//def add = {(a: Int,b: Int)=> a + b}
//def multiply = {(a: Int,b: Int)=> a*b}
//
//def newSumFunction = combineFunction(add,0)_
//
//newSumFunction(squareFun)(1,3)
//
//def prodFunction = combineFunction(multiply,1)_
//prodFunction(x=>x)(1,4)