Summon a Semigroup for Maybe, defined as an enum

summon-semigroup-Maybe.scala

// using scala 3.1.0
// using lib org.typelevel::cats-core:2.6.1

package good

import cats.Semigroup
import cats.syntax.all.*

enum Maybe[+A]:
  case Just(a: A)
  case Nothing

given [A: Semigroup]: Semigroup[Maybe[A]] with
  def combine(a1: Maybe[A], a2: Maybe[A]): Maybe[A] =
    (a1, a2) match
      case (Maybe.Nothing, _) => Maybe.Nothing
      case (_, Maybe.Nothing) => Maybe.Nothing
      case (a1 @ Maybe.Just(_), a2 @ Maybe.Just(_)) => a1.combine(a2)

given [A: Semigroup]: Semigroup[Maybe.Just[A]] with
  def combine(a1: Maybe.Just[A], a2: Maybe.Just[A]): Maybe.Just[A] =
    val Maybe.Just(x) = a1
    val Maybe.Just(y) = a2
    Maybe.Just(x combine y)

@main def Main =
  println(Maybe.Just(1) combine Maybe.Just(2))
  println((Maybe.Nothing: Maybe[Int]) combine Maybe.Just(2))

issue with this is that derives clauses will only define a single given for an enum - perhaps the compiler can be adapted to derive a given for each case?