class Steep::Interface::Interface::Combination

def to_s
  case operator
  when :overload
    "{ #{types.map(&:to_s).join(" | ")} }"
  when :union
    "[#{types.map(&:to_s).join(" | ")}]"
  when :intersection
    "[#{types.map(&:to_s).join(" & ")}]"
  end
end