CS153, Class 16: Vectors

Overview:
* Problems with lists.
* A solution: Vectors.
* Side note: The begin construct.
* Lab.

Notes:
* Happy valentine's day
* Are there questions on exam 1?
  + Q&A now in the exam.
  + Extended deadline.
* Read "Design Patterns and Higher-Order Procedures"
  + Sorry, it's somewhat long
* Read pp. 69-73 of Bailey.
* Cool math talk today at 4:30.  Go and get extra credit.
  a^p mod p = a for primes p

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C++-ers:

Rewrite
  (define exponent 
     (lambda (val power)
       (cond
         ((zero? power) 1)
         ((even? power) (square (exponent val (/ power 2))))
         (else (* val (exponent val (- power 1)))))))
in C++ without using recursion

Question: Does Scheme have iteration?
Answer: Yes: Named let is sort of like iteration.  "do" is
  Scheme's primary iteration mechanism.

Question: Does Scheme have pointers?
Answer: Yes.  Pairs are pairs of pointers.

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PReflection:

Why are lists cool?
* Defined recursively, so easy to recurse over

Do the lab

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Reflection, Revisited

* When students don't show up, should I call them?

* Use quote to create vector literals
  #(3.14159 #2.718) vs. '#(3.14159 2.718)
  #(pi e) vs '#(pi e)

* Why use vector rather than #?
  (vector pi e) vs '#(pi e)
  (define two-students (vector "Ogechi" "Katherine")) vs. 
  (define dos-estudientes '#("Ogechi" "Katherine"))

  (vector-set! two-students 0 "Oge")
  (vector-set! dos-estudientes 1 "Kat")

* What is #100(1 2 3)?

* Consider
  (define emu (vector 1 2 3))
  (define shark (list (vector-set! emu 1 2)))
  What is emu?
  What is shark?

* "Use" is ambguous
  + "Use as a helper"
  + "Use as a pattern"

(define NAME
  (lambda (lst)
    (if (null? lst)
        null
        (cons (SOMETHING (car lst)) (NAME (cdr lst))))))