Stack <- R6Class("Stack")  # Push and pop values onto an internal vector
  initialize <- function(values = list())
  push <- function(x)
  pop <- function()
  size <- function()
Range <- new_class("Range")
  method(format, Range) <- function(x, ...)
moving_average <- function(x, n = 5)  # Compute a moving average over a numeric vector
greet <- function(name = "world", greeting = "hello")
load_data <- function(path, sep = ",", na.strings = c("NA", "", "n/a"), stringsAsFactors = FALSE)  # Load a CSV with sensible defaults
server <- function(input, output, session)
setGeneric("distance_to_origin")
setMethod("distance_to_origin", "Point")
setClass("Point")
