lazy_example.scala

import scala.annotation.tailrec
import cats.Eval

final class ParMetaData(connectiveUsedFn: Eval[Boolean]) {
  lazy val connectiveUsed: Eval[Boolean] = connectiveUsedFn
}
sealed trait Par {
  protected def meta: ParMetaData
  lazy val connectiveUsed: Boolean = meta.connectiveUsed.value
}
sealed trait Expr extends Par

def cUsedParSeq(ps: Seq[Par]) = ps.exists(_.connectiveUsed)
def connectiveUsedParProc(ps: Seq[Par]): Boolean = cUsedParSeq(ps)
def connectiveUsedGInt(v: Long): Boolean = false

class ParProc(val ps: Seq[Par], protected val meta: ParMetaData) extends Par {}
object ParProc {
  def apply(ps: Seq[Par]): ParProc = createParProc(ps)
  def createParProc(ps: Seq[Par]): ParProc = {
    val meta = new ParMetaData(Eval.later(connectiveUsedParProc(ps)))
    new ParProc(ps, meta)
  }
}

final class GInt(val v: Long, protected val meta: ParMetaData) extends Expr
object GInt {
  def apply(v: Long): GInt = createGInt(v)
  def createGInt(v: Long): GInt = {
    val meta = new ParMetaData(Eval.later(connectiveUsedGInt(v)))
    new GInt(v, meta)
  }
}

@tailrec
def hugePar(n: Int, par: Par = GInt(0)): Par =
  if (n == 0) par
  else hugePar(n - 1, ParProc(Seq(par)))

val par = hugePar(5000)
println("!!!!")
println(par.connectiveUsed)