PersonBuilder.scala

import PersonBuilder._
import shapeless._

case class Person(name: String, age: Int)

object PersonBuilder {
  def apply() = new PersonBuilder[Start](Person("", 0))

  trait Start

  trait StepName
  trait StepAge
  type AllSteps = StepAge with StepName
}

class PersonBuilder[StepsDone] private (person: Person) {
  def name(name: String)(implicit ev: StepsDone <:!< StepName) = {
    new PersonBuilder[StepsDone with StepName](person.copy(name = name))
  }

  def age(age: Int)(implicit ev: StepsDone <:!< StepAge) = {
    new PersonBuilder[StepsDone with StepAge](person.copy(age = age))
  }

  def build()(implicit ev: StepsDone <:< AllSteps): Person = {
    person
  }
}