Lab 2:

1) define a piece of compound data to represent desks, which are a kind of
office furniture.  A desk has a width, a height, and a depth.

2) develop the 'furniture-footprint' function that consumes a desk and returns
its footprint---that is, how much floor space it takes up.  Write test cases
first.

3) extend the definition of office furniture to include Bookshelves.  A
bookshelf has a depth, a number of shelves, and a shelf-width.

4) extend test-cases and definition of of the furniture-footprint function so
that it handles bookshelves, as well as desks.


5) Define the AE language we described in class.

6) Develop the evaluation method we described in class.

7) Develop the method num-nums, that accepts an AE and returns a number
indicating how many numbers it contains.

8) Develop the method num-adds, that accepts an AE and returns the number
of additions it contains.

9) Develop the method swap-adds, that accepts an AE and returns a new AE where
the left and right terms of every addition are swapped.