trait P[+T] extension [T](inline parse0: P[T]) { inline def |[V >: T](inline other: P[V]): P[V] = ??? } // Works if:  // - parse0 is passed by value or // - when rep has empty argument list, i.e: def rep[V]()(using repeater: Implicits.Repeater[T, V]): P[V] extension [T](inline parse0: => P[T]) { inline def rep[V](inline min: Int = 0)(using repeater: Implicits.Repeater[T, V]): P[V] = ??? } object Implicits { trait Repeater[-T, R] object Repeater { implicit def GenericRepeaterImplicit[T]: Repeater[T, Seq[T]] = ??? } } sealed trait RegexTree abstract class Node extends RegexTree class CharClassIntersection() extends Node def classItem: P[RegexTree] = ??? def charClassIntersection: P[CharClassIntersection] = ??? def x = { (charClassIntersection.rep() | classItem.rep()) }

-- [E172] Type Error: /Users/wmazur/projects/dotty/bisect/main.scala:31:33 ----- 31 | (charClassIntersection.rep() | classItem.rep()) | ^^^^^^^^^^^^^^^ |No given instance of type Implicits.Repeater[RegexTree, V] was found. |I found: | | Implicits.Repeater.GenericRepeaterImplicit[T] | |But method GenericRepeaterImplicit in object Repeater does not match type Implicits.Repeater[RegexTree, V] | |where: V is a type variable with constraint <: Seq[CharClassIntersection]