def Test = { val left: Parser[String] = ??? val right: Parser[Int] = ??? val both = left && right val works = both.map(Ior.Both.apply) val fails = (left && right).map(Ior.Both.apply) } trait Parser[T]: final def &&[T2](other: Parser[T2])(implicit zip: Zip[T, T2]): Parser[zip.Out] = ??? final def map[T2](f: T => T2): Parser[T2] = ??? infix trait Ior[+A, +B] object Ior: final case class Both[+A, +B](a: A, b: B) extends (A Ior B) trait Zip[In1, In2]: type Out object Zip { type Out[In1, In2, O] = Zip[In1, In2] { type Out = O } implicit def zip2[_1, _2]: Zip.Out[_1, _2, (_1, _2)] = ??? } 

 |def Test = { |^ |Recursion limit exceeded. |Maybe there is an illegal cyclic reference? |If that's not the case, you could also try to increase the stacksize using the -Xss JVM option. |For the unprocessed stack trace, compile with -Yno-decode-stacktraces. |A recurring operation is (inner to outer): | | check fully defined A | check fully defined (A, B) | check fully defined Tuple.Elem[(A, B), (param)1] | check fully defined A | check fully defined (A, B) | check fully defined Tuple.Elem[(A, B), (param)1] | check fully defined A | check fully defined (A, B) | check fully defined Tuple.Elem[(A, B), (param)1] | check fully defined A | ... | | check fully defined A | check fully defined (A, B) | check fully defined Tuple.Elem[(A, B), (param)1] | check fully defined A | check fully defined (A, B) | check fully defined Tuple.Elem[(A, B), (param)1] | check fully defined A | check fully defined (A, B) | check fully defined (A, B) | check fully defined Tuple.Elem[(A, B), (param)1] 7 errors found Compilation failed