if (!"package:R6" %in% search()) {
  library(R6)
}


# Class


Game <- R6Class("Game",

    public = list(

        # Properties:

        a     = 0,
        b     = 0,
        sum   = 0,


        # Functions:

        run = function() {
            part_1()
            part_2()
            part_3()
        },

        part_1 = function() {
            self$a = 10
            return(self$a)
        },

        part_2 = function() {
            self$b = 20
            return(self$b)
        },

        part_3 = function() {
          self$sum = self$a + self$b
          return(self$sum)
        }

     )

)
# Instantiate an object base on a class.
game <- Game$new()

# Run function that runs through all other functions.
game$run()