HtDP 7

start with Posn

Square (nw, length)
Circle (center, radius)

Find perimeter of each

Define the perimeter function... that takes both
       - data definition
       - communicate to Java (interface)
       - try
       - add to classes
       - glory

Sometimes we know we want to write 'perimeter' first, so we discover our needs top-down

Write translate (dx, dy)