Functions can be arguments. starburst draws a burst with any shape at each end. starburst 5, 50, dot draws a default black dot at each end. Can you change the program to draw a reddot at each end?
Bigger Fireworks pass a bigger function
Instead of drawing a dot at each end, try creating a function that draws some other shape at each end of the starburst. Can you draw a smaller starburst at each end of the big starburst?
More Ideas
starburst = (x, y, shape) ->
for z in [1..x]
fd y
do shape
bk y
rt 360 / x
reddot = ->
dot red, 20
pen gold, 3
starburst 5, 50, dot