CSC151 2009F, Class 38: Trees

Admin:
* Reading for tomorrow: Analyzing Procedures.
* One of my former advisees made the front page of NYT Arts & Leisure
* Congratulations! to men's soccer.
* You know that you're in too small a town when the local radio 
  station reports on when one of your students had surgery.  
  * (Or maybe that's just football in Iowa.)
* Exam 2 returned.  I hope to have an answer key ready later this week.
  * THERE IS MORE TO LIFE THAN GRADING!
    (So comments on the second half of the exam are a bit briefer than
     those on the first half of the exam.)
* Are there questions on Lab Writeup 5?
* Are there questions on Assignment 7?

Overview:
* Notes on exam, lab, and assignment.
* Thinking about trees in terms of cons.
* Thinking about trees recursively.
* Writing recursive tree procedures.

Questions on Writeup 5
* The pictures should be turned in in hardcopy.  Please don't scan them.

Notes on reverse:
* Drawing on physical whiteboard.  (Sorry.)

* What is a list?
  * null is a list (the empty list)
  * if L is a list, (cons X L)
* Looks a lot like our def'n of the natural numbers
  * 0 is a natural number
  * If N is a natural number, 1+N is a natural number

* cons can take non-lists as the second parameter

* A color tree is a pair structure defined as follows
  * A color is a color tree
  * If C1 and C2 are color trees, than so is (cons C1 C2)