plot_cauldron

revelio <- function(object){NA}
setGeneric("revelio")
setMethod("revelio", signature(object = "Cauldron"), 
          function(object) {
            y <- -10:10
            x <- y ** 2
            z <- seq(20, 80, length.out = 100)
            plot(x, y, type = 'l', ylim=c(-4, 4), 
                 xlab = "", ylab = "", axes=FALSE)
            lines(-x + 100, y)
            lines(z, rep(-4.2, 100))
            lines(z, rep(4.2, 100))
            lines(z, 0.0012*(z - 50)**2 + 3)
            lines(z, 0.0012*(z - 50)**2 + 2.5)
            text(x = 50, y = 0, 
                 labels = "I am a cauldron.")
          })

revelio(caul)


setMethod("revelio", signature(object = "Cabbage"), 
          function(object) {
            x <- seq(-2, 2, length.out = 1000)
            y <- sqrt(4 - x**2)
            plot(x, y, type = 'l', 
                 xlim = c(-5, 5), ylim = c(-2,2), 
                 xlab = "", ylab = "", axes=FALSE)
            lines(x, -y)
            text(x = 0, y = 0, 
                 labels = "I am a cabbage.")
          })

revelio(cabb)