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class TypeConstructor {
type TypeArg
}
trait List[+T] extends TypeConstructor { type TypeArg <: T }
trait Set[T] extends TypeConstructor { type TypeArg <: T }
object obj extends List[Number] with Set[Exception] {
val x: TypeArg = ???
val n: Number = x
val e: Exception = x
}
abstract class Functor[F <: TypeConstructor] {
def map[A, B](f: F { type TypeArg <: A }): F { type TypeArg <: B }
}
object ListFunctor extends Functor[List] {
override def map[A, B](f: List { type TypeArg <: A }): List { type TypeArg <: B } = ???
}
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