Quick example using Iron with an optional refined type

readme.md

If you have scala-cli installed, you can run the file like a script. Just download it and run chmod +x iron.scala && ./iron.scala

iron.scala

#!/usr/bin/env -S scala-cli shebang -S 3
//> using toolkit typelevel:default
//> using dep io.github.iltotore::iron:2.6.0
//> using dep io.github.iltotore::iron-cats:2.6.0
//> using dep io.github.iltotore::iron-circe:2.6.0

import cats.*
import cats.data.EitherNec
import cats.data.NonEmptyChain
import cats.effect.*
import cats.effect.std.Console
import cats.syntax.all.*
import io.circe.*
import io.circe.derivation.*
import io.circe.syntax.*
import io.github.iltotore.iron.*
import io.github.iltotore.iron.cats.*
import io.github.iltotore.iron.circe.given
import io.github.iltotore.iron.constraint.all.*

given Configuration = Configuration.default.withSnakeCaseMemberNames

type ValidName  = DescribedAs[Head[Letter] & MinLength[1], "a name is required, must start with a letter"]
type ValidTitle = DescribedAs[Head[Letter] & MinLength[1], "the title cannot be blank, must start with a letter"]

case class Person(name: String :| ValidName, title: Option[String :| ValidTitle]) derives ConfiguredCodec

object Person:
  def create(name: String, title: Option[String]): EitherNec[String, Person] =
    (name.refineNec[ValidName], title.traverse(_.refineNec[ValidTitle])).parMapN(Person.apply)

object EitherNecIOOps:
  extension [E: Show, A](nec: EitherNec[E, A])
    def liftToIO: IO[A] = nec.leftMap(c => IllegalArgumentException(c.show)).liftTo[IO]

type NecStringThrow <: IllegalArgumentException
object NecStringThrow:
  def apply(c: NonEmptyChain[String]): NecStringThrow =
    new IllegalArgumentException(c.show).asInstanceOf[NecStringThrow]

object app extends IOApp.Simple:
  import EitherNecIOOps.*
  override def run: IO[Unit] = for
    _ <- Console[IO].println("enter name")
    n <- Console[IO].readLine
    _ <- Console[IO].println("enter title (leave blank for no title)")
    t <- Console[IO].readLine
    tV = if (t.isEmpty()) then None else Some(t)
    person <- Person.create(n, tV).liftToIO
    _      <- IO.println(person)
    _      <- IO.println(person.asJson.spaces2)
  yield ExitCode.Success