1-4-5.rkt~

;; The first three lines of this file were inserted by DrRacket. They record metadata
;; about the language level of this file in a form that our tools can easily process.
#reader(lib "htdp-beginner-reader.ss" "lang")((modname 1-4-5) (read-case-sensitive #t) (teachpacks ()) (htdp-settings #(#t constructor repeating-decimal #f #t none #f () #f)))
; An LR (short for launching rocket) is one of:
; – "resting"
; – NonnegativeNumber
; interpretation "resting" represents a grounded rocket
; a number denotes the height of a rocket in flight