;; EXERCISE GOAL: to develop programs to show grades as a bar graph

;; USEFUL CONSTANTS

(define GRADE-WIDTH 20)
(define GRADE-HEIGHT 10)
(define PICTURE-WIDTH 125)
(define PICTURE-HEIGHT 100)

;; 1. Provide a data definition for list-of-image

;; 2. Write a function compose-images that consumes a list of images
;; and produces an image.  The produced image is the combination of
;; all the images in the input list (hint: use image+ (207) or overlay/xy (208))

;; 3. Write a program count-grades that consumes a symbol (a letter
;; grade) and a list of symbols (letter grades) and produces the number
;; of times the given grade appears in the list.

;; 4a. Write a program grade-to-bar that consumes a number of grades
;; and a bar color, and produces a rectangle whose height is
;; proportional to the number of grades, or an empty image if there
;; are no grades.  Use the constants provided.

;; 4b. Write a program grade-bar-image that consumes a letter grade, bar
;; color, x-coordinate for the bar and a gradelist and produces an
;; image.  The image should be of a bar whose height is proportional
;; to the number of times the grade appears in the list.  Use the
;; constants provided. (hint: do this first with the bar growing
;; downwards in the image, then refine your function to draw the bar
;; growing upwards)

;; 5. Write a program grades-to-bars that consumes a list of symbols
;; (a list of grades) and produces a list of 3 images.  The first is a
;; red bar at x coordinate 25 for the A grades, the second a
;; blue bar at x coordinate 50 for the B grades, the second a
;; green bar at x coordinate 75 for the C grades.

;; 6. Write a program graph-grades that consumes a list of grades and
;; produces an image of the bar graph for the grades.

;; SUPER-CHALLENGE : Redo this exercise to animate the graph
;; construction as you process the grades