ContainmentSet/BoolSet

BoolSet.scala

import cats.Eq, cats.syntax.eq._

case class BoolSet[A](p: A => Boolean)(implicit eq: Eq[A]) {
  def add(a1: A): BoolSet[A] = copy(p = a => p(a) || a === a1)
  def contains(a: A): Boolean = p(a)
  def remove(a: A): BoolSet[A] = copy(p = a1 => a1 =!= a && p(a1))
  def union(other: BoolSet[A]): BoolSet[A] = copy(p = a => p(a) || other.p(a))
  def intersect(other: BoolSet[A]): BoolSet[A] = copy(p = a => p(a) && other.p(a))
  def difference(other: BoolSet[A]): BoolSet[A] = copy(p = a => p(a) && !other.p(a))
  def complement: BoolSet[A] = copy(p = a => !p(a))
}

object BoolSet {

  // For testing
  implicit val eqInt: Eq[Int] = new Eq[Int] {
    override def eqv(x: Int, y: Int): Boolean = x == y
  }

  def apply[A](as: A*)(implicit eq: Eq[A]): BoolSet[A] =
    BoolSet((a: A) => as.foldLeft(false)((p, a1) => p || a1 === a))

}