Never ever write a loop

scala

/* live demo ZIO.loop
    https://scastie.scala-lang.org/butcherless/IEXLzpbZSL28zmFK166IKA/2
*/
package com.cmartin.utils

import zio.{App, ExitCode, UIO, ZIO}

object ZioLoopDemo extends App {

  import zio.console._

  /**
    * Loops with the specified effectual function, collecting the results into a
    * list. The moral equivalent of:
    *
    * {{{
    * var s  = initial
    * var as = List.empty[A]
    *
    * while (cont(s)) {
    *   as = body(s) :: as
    *   s  = inc(s)
    * }
    *
    * as.reverse
    * }}}
    *
    * def loop[R, E, A, S](initial: S)(cont: S => Boolean, inc: S => S)(body: S => ZIO[R, E, A]): ZIO[R, E, List[A]] =
    * if (cont(initial))
    *   body(initial).flatMap(a => loop(inc(initial))(cont, inc)(body).map(as => a :: as))
    * else
    *   ZIO.succeedNow(List.empty[A])
    */
  /*
   * concepts
   */
  /*
   * result container
   */
  case class MyResult(a: Double, text: String)
  case class MyInfo(a: Int)
  /*
   * initial state of the business information
   */
  val initial: MyInfo = MyInfo(10)
  /*
   * function that determines the continuation of the processing loop
   */
  def cont(info: MyInfo): Boolean = info.a > 0
  /*
   * function that gets the next status of business information
   */
  def dec(info: MyInfo): MyInfo = MyInfo(info.a - 1)
  /*
   * business function
   */
  def body(info: MyInfo): UIO[MyResult] =
    UIO(MyResult(info.a.toDouble, intTypeText(info.a)))
  /*
   * helper functions
   */
  def intTypeText(a: Int)                = if (a % 2 == 0) "even" else "odd"
  def prettyPrint[A](l: List[A]): String = l.mkString("\n\t", "\n\t", "\n")

  /*
   * program
   */
  val program = for {
    _             <- putStrLn("zio loop demo:")
    evenOrOddList <- ZIO.loop(initial)(cont, dec)(body)
    _             <- putStrLn(s"-> evenOrOddList => ${prettyPrint(evenOrOddList)}")
  } yield ()

  // main function, needs exit = 0 [OK] or exit > 0 [ERROR]
  // Here the interpreter runs the program and perform side-effects
  override def run(args: List[String]): ZIO[zio.ZEnv, Nothing, ExitCode] = {
    (program as ExitCode.success)
      .catchAllCause(cause => putStrLn(s"${cause.prettyPrint}") as ExitCode.failure)
  }
}

Live demo: https://scastie.scala-lang.org/butcherless/IEXLzpbZSL28zmFK166IKA/2