Examples of ScalaZ lenses and states

ScalazLenses.scala

import scalaz._
import Scalaz._
import Lens._

/*

Examples of Scalaz lenses

*/

// Model

case class Address(street: String, city: String, state: String, zip: Int)

case class Person(firstName: String, lastName: String, address: Address)

case class Department(name: String, numberOfEmployees: Int)

case class Company(departments: Map[Int, Department])

object ScalazLenses {

  // creating lens with lensu
  val streetL : Address @> String   = lensu((a,s) => a.copy(street = s), _.street)
  val zipL    : Address @> Int      = lensu((a,z) => a.copy(zip = z), _.zip)

  // alternative method to create lens: lensg
  val addressL : Person @> Address  = lensg( p => a => p.copy(address = a), _.address)

  // composing lenses
  // Person @> Int
  val personZipL = addressL >=> zipL // same as andThen
  val personZipL2 = addressL andThen zipL


  // From Lens to State
  
  // Set value :State[Person, Address] 
  def setAddress(a :Address) = addressL := a
  
  // modify value
  val incrementZipCode = addressL >=> zipL %= (_+1)
  // same using numeric modify +=
  val incrementZipCode2 = addressL >=> zipL += 1


  // Lenses and Maps
  val numberOfEmployeesL : Department @> Int = lensu((d,c) => d.copy(numberOfEmployees = c), _.numberOfEmployees)
  val departmentsL: Company @>  Map[Int, Department] = lensu((c,d) => c.copy(departments = d), _.departments)
  
  // modify existing map entry. Will throw exception if key not found
  def addEmployee(depId: Int) = departmentsL.at(depId) >=> numberOfEmployeesL += 1
  
  //same but using optional
  def addEmployee2(depId: Int) = departmentsL.member(depId) %= {
    case Some(d) => Some(numberOfEmployeesL.set(d, d.numberOfEmployees + 1))
    case None    => Some(Department("New Department", 1))
  }
  

}