scala2-3-MonoidTypeClassInstance-revisited1.scala

given StringMonoid: Monoid[String] with
  def unit: String = ""
  extension (s: String) def combine(other: String): String = s + other

"2" <+> ("3" <+> "4")             // "234"
("2" <+> "3") <+> "4"             // "234"
StringMonoid.unit <+> "2"         // "2"
"2" <+> StringMonoid.unit         // "2"

"2" `combine` ("3" `combine` "4")
("2" `combine` "3") `combine` "4"
StringMonoid.unit `combine` "2"
"2" `combine` StringMonoid.unit

"2" combine {"3" combine {"4"}}
"2" combine {"3"} combine {"4"}
StringMonoid.unit combine {"2"}
"2" combine {StringMonoid.unit}