22b. List Exercises 4

1. count-down-odd: number(start) number(end) -> list of numbers. Generate a list of all of the odd numbers from end down to start (inclusive).

    (count-down-odd 5 10) => (list 9 7 5)
    (count-down-odd 5 5) => (list 5)
   

2. dinosaur: list of numbers -> list of strings. Change a list of numbers, all of which will be between 0 and 7 inclusive, into a list of the corresponding letters from the word dinosaur.

    (dinosaur (list 4 5 0)) => (list "s" "a" "d")
   

3. shaper: list of numbers -> image. Choose an image based on the number (1=triangle, 2=square, 3=circle; pick colors and sizes you like). Randomly place the image on a 400x300 gray rectangle.

   Advanced bonus: the list of numbers comes in pairs - the first number selects the shape and the second number selects its size.

    (shaper (list 1 50 3 20)) 
   

   The call above would place a triangle of side length 50 and a circle of radius 20.