CSC151.02 2003F: Numeric Recursion, Continued

Admin:
* Final reminder for tonight's talk 7pm: Liberating Learning in the Sciences and Engineering: Lessons from Feminist and Radical Pedagogies
* Grammar: "Pedagogy" approximately equals "Way of teaching"
* No reading for tomorrow
* Does anyone use the EBoards?  How?
* Grinnell Homecoming Parade, 5:30 p.m. Central Park

Overview:
* Review
* Lab, Continued
* Reflections

Review:
* What is the standard form of a recursive procedure?
(define PROCEDURE
  (lambda (PARAMETER)
    (if BASETEST
        BASECASE
        (REBIGGIFY (PROCEDURE (SMALLIFIED PARAMETER))))))
(define PROCEDURE
  (lambda (PARAMETER)
    (if BASETEST
        BASECASE
        (EXPAND (PROCEDURE (SIMPLIFY PARAMETER))))))
* How do we specialize that form for numeric recursion?
(define PROCEDURE
  (lambda (n)
    (if (zero? n)
        BASECASE
        (REBIGGIFY (PROCEDURE (- n 1))))))
* What are some particular examples?
Factorial:
* Procedure: factorial
* Basecase: 1
* Expand: Multiply by n
(define factorial
  (lambda (n)
    (if (zero? n)
        1
        (* n (factorial (- n 1))))))
Count-down:
(define count-down
  (lambda (n)
    (if (zero? n)
        null
        (cons n (count-down (- n 1))))))

How *not* to write digit-of?

(define digit-of?
  (lambda (dig num)
    (member?
     (string-ref (number->string dig) 0)
     (string->list (number->string num)))))

(define member?
  (lambda (val lst)
    (and (not (null? lst))
         (or (equal? val (car lst))
             (member? val (cdr lst))))))

Conclusion: Sam Sux at Tux