Notes: Monday 24 February 2003

Schedule

• Now: Exam 1 due
• Before 10 March: Read rest of GEB part I (Chapters 2-4 and 6-9, in addition to Chapters 1 and 5 you have already read).
• Friday, 14 March: Problem Set 5: Wahoo! Auctions

Notes

Mutation Procedures:

• (set! Name Expression) — evaluate Expression and replace the value associated with Name with the value of Expression
• (set-car! Expression₀ Expression₁) — evaluate Expression₀ and Expression₁ and store the value of Expression₁ in the car part of the value of Expression₀. Expression₀ must evaluate to a cons pair.
• (set-cdr! Expression₀ Expression₁) — evaluate Expression₀ and Expression₁ and store the value of Expression₁ in the cdr part of the value of Expression₀. Expression₀ must evaluate to a cons pair.

(define (adelphiaize! lst)
   (if (null? lst) 
       (void) ; nothing to return
       (begin
         (if (< (car lst) 0) (set-car! lst 0))
         (adelphiaize! (cdr lst)))))

Why is mutation scary?

Why is mutation useful?

Why do our evaluation rules fail when we allow mutation?

Would it be possible to create a circular list without using set-cdr!?

	CS 200: Computer Science Department of Computer Science University of Virginia Circle Fractal by Ramsey Arnaoot and Qi Wang	cs200-staff@cs.virginia.edu Using these Materials