Notes: Wednesday 25 February 2004

Schedule

• Friday, 5 March: Problem Set 5
• Before 15 March: Read rest of GEB part I (Chapters 2-4 and 6-9, in addition to Chapters 1 and 5 you have already read).

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 (map! f lst)
   (if (null? lst) (void)
       (begin
           (set-car! lst (f (car lst)))
           (map! f (cdr lst)))))

Why is mutation scary?

Why is mutation useful?

Why do our substitution evaluation rules fail when we allow mutation?

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