CSC151 2010S, Class 21: Naming Local Values

Overview:
* Questions on assignment 5.
* Questions on the reading.
* Lab.

Admin:
* Don't forget to email me if you can't make it to class.
* I'm way behind on grading, as you can tell.  Hopefully, I'll have time soon.
* What questions are there on Assignment 5?

Questions on Assignment 5
* Is it important that we use the same procedure names as you gave us?  Yes.
  * Why?
  * So that I can do some automated testing.  (If, for some reason, I decided to grade your assignment.)
* Why are some parts of this so hard?  It it inherent in the language?
  * Your knowledge is limited.  We'll learn some easier ways to do some of these things later.
  * It's purposefully hard because the hard approach can help you learn some important concepts.
* How much should I turn the turtle in the centered polygon?
  * Draw a diagram.
  * Sam is an idiot.  sin and cos work in radians, but turtles work in degrees.
  * To convert from radians to degrees: multiply by 180/pi.  To convert from degrees to radians, multiply by pi/180.
* Can you explain the use of repeat, particularly with parameters from the main procedure?
(define turtle-stuff!
  (lambda (turtle distance angle)
    (repeat 5
            (lambda (t)
              (turtle-forward! t distance)
              (turtle-turn! t angle))
            turtle)))
    
(define turtle-stuff2!
  (lambda (turtle distance angle)
    (repeat 5
            (lambda ()
              (turtle-forward! turtle distance)
              (turtle-turn! turtle angle)))))

* Can we nest repeats?  Certainly.  Here's an indirect nesting.
(define repeat-turtle-stuff2!
  (lambda (turtle times distance angle)
    (repeat times
            (lambda ()
              (turtle-stuff2! turtle distance angle)))))
* Why the lambda?
  * Repeat HAS TO TAKE A PROCEDURE as its second parameter.  (turtle-stuff2! turtle distance angle) is a value.
(define repeat-turtle-stuff2!
  (lambda (turtle times distance angle)
    (repeat times
            turtle-stuff2! 
            turtle 
            distance 
            angle)))))
* What do you mean by "reset the turtle every time"?
  * When your procedure is done, the procedure should be back in its original position and orientation?

---

(define turtle-square!
  (lambda (turtle edge)
    (repeat 4
            (lambda ()
              (turtle-forward! turtle edge)
              (turtle-turn! turtle 90)))))

(for-each (lambda (n)
              (turtle-forward! tommy n)
              (turtle-turn! tommy n)
              (turtle-square! tommy n))
            (list-drop (iota 20) 1))