[Feature #20318] Example

example.rb

      # before
      def balance(*args)
        case args
        in [RedFork[a, xk, xv, b], yk, yv, RedFork[c, zk, zv, d]]
          RedFork[BlackFork[a, xk, xv, b], yk, yv, BlackFork[c, zk, zv, d]]
        in [RedFork[RedFork[a, xk, xv, b], yk, yv, c], zk, zv, d]
          RedFork[BlackFork[a, xk, xv, b], yk, yv, BlackFork[c, zk, zv, d]]
        in [RedFork[a, xk, xv, RedFork[b, yk, yv, c]], zk, zv, d]
          RedFork[BlackFork[a, xk, xv, b], yk, yv, BlackFork[c, zk, zv, d]]
        in [a, xk, xv, RedFork[b, yk, yv, RedFork[c, zk, zv, d]]]
          RedFork[BlackFork[a, xk, xv, b], yk, yv, BlackFork[c, zk, zv, d]]
        in [a, xk, xv, RedFork[RedFork[b, yk, yv, c], zk, zv, d]]
          RedFork[BlackFork[a, xk, xv, b], yk, yv, BlackFork[c, zk, zv, d]]
        in [a, xk, xv, b]
          BlackFork[a, xk, xv, b]
        end
      end

      # after
      def balance(...)
      in [RedFork[a, xk, xv, b], yk, yv, RedFork[c, zk, zv, d]]
        RedFork[BlackFork[a, xk, xv, b], yk, yv, BlackFork[c, zk, zv, d]]
      in [RedFork[RedFork[a, xk, xv, b], yk, yv, c], zk, zv, d]
        RedFork[BlackFork[a, xk, xv, b], yk, yv, BlackFork[c, zk, zv, d]]
      in [RedFork[a, xk, xv, RedFork[b, yk, yv, c]], zk, zv, d]
        RedFork[BlackFork[a, xk, xv, b], yk, yv, BlackFork[c, zk, zv, d]]
      in [a, xk, xv, RedFork[b, yk, yv, RedFork[c, zk, zv, d]]]
        RedFork[BlackFork[a, xk, xv, b], yk, yv, BlackFork[c, zk, zv, d]]
      in [a, xk, xv, RedFork[RedFork[b, yk, yv, c], zk, zv, d]]
        RedFork[BlackFork[a, xk, xv, b], yk, yv, BlackFork[c, zk, zv, d]]
      in [a, xk, xv, b]
        BlackFork[a, xk, xv, b]
      end