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   1 * form
   2   * "(function element0 ...)"
   3 * building blocks of racket semantics
   4 ** booleans
   5    * "(zero? 1)" "(zero? (sub1 1))"
   6 ** symbols
   7    * a-z+-/*=<>?!_^
   8    * (symbol=? 'foo 'FoO) true or false?
   9 ** numbers
  10    * "(expt 53 53)" "(= (/ 4 6) 2/3 (/ 2 3))" "(= (/ 4.0 6) 0.6666666666666666)"
  11    * numbers like 4.0 are floating point numbers
  12    * irrational numbers
  13 ** strings
  14    * "tutti frutti"
  15    * (equal? (string-append "tutti" "frutti") "tuttifrutti")
  16    * (equal?(string-append "tutti" " " "frutti") "tutti frutti")
  17    * substring, string-ref, string=?
  18 ** lists
  19    * super duper important in racket
  20 *** cons cells
  21     * (equal?(list 1 2) (cons 2 (cons 3 empty)))
  22     * same as linked lists in other languages
  23 **** functions for cons cells
  24      * (equal?(cons 1 2) '(1 . 2))
  25      * (define cell (cons 'a 'b)) (equal?(car cell) 'a) (equal?(cdr cell) 'b)
  26 *** lists and list functions
  27     * (equal?'() empty (list))
  28 **** cons function
  29      * (equal?(cons 'chicken empty) '(chicken))
  30      * empty is used to terminate lists in racket, so '(chicken) has
  31        an implicit empty
  32      * what do you get when you add a chicken to an empty list? a list with
  33        a chicken in it
  34      * (equal?(cons 'pork '(beef chicken)) '(pork beef chicken))
  35      * (equal?(cons 'beef (cons 'chicken '())) '(beef chicken))
  36      * (equal?(cons 'pork (cons 'beef (cons 'chicken '())))
  37           '(pork beef chicken))
  38 **** list function
  39      * (equal?(list 'pork 'beef 'chicken) '(pork beef chicken))
  40 **** first and rest functions
  41      * (equal?(first (cons 'pork (cons 'beef (cons 'chicken empty)))) 'pork)
  42      * (equal?(rest (list 'pork 'beef 'chicken)) '(beef chicken))
  43      * (equal?(first (rest ('pork beef chicken))) 'beef)
  44      * how do you get the third item?
  45      * what happens when you try to get the fourth item?
  46 **** nested lists
  47      * (equal?(list 'cat (list 'duck 'bat) 'ant) '(cat (duck bat) ant))
  48      * all lists are made of cons cells
  49      * (equal?(first '((peas carrots tomatoes) (pork beef chicken)))
  50           (peas carrots tomatoes))
  51      * (equal?(rest '(peas carrots tomatoes)) '(carrots tomatoes))
  52      * (equal?(rest (first '((peas carrots tomatoes) (pork beef chicken))))
  53           '(carrots tomatoes))
  54      * second third ... tenth built-in
  55 ** structures
  56    structures group things together, like lists. structures group a
  57    fixed number of items, unlike lists.
  58    example: student has name ID dorm.
  59 *** structure basics
  60     * "(struct student (name id# dorm))"
  61       this defines a structure, but doesn't actually create one.
  62     * "(define freshman1 (student 'Joe 1234 'NewHall))"
  63       this creates a structure
  64     * fields: name, id#, dorm
  65     * (equal? (student-name freshman1) 'Joe)
  66 *** nesting structures
  67     * (struct student-body (freshmen sophomores juniors seniors))
  68     * (define all-student (list a b) (list) (list c d) (list e))
  69     * a b c d e can all be student struct instances
  70     * nested selectors:
  71       * (student-name (first (student-body-freshmen all-students)))
  72 *** structure transparency
  73     * default is opaque
  74     * opaque means comparison is by identity not value
  75     * (equal? false (equal? (student 'joe 1 'dorm) (student 'joe 1 'dorm)))
  76     * (equal? true (equal? freshman1 freshman1))
  77     * transparent structs are compared on value
  78     * create transparent struct type: (struct a (b) #:transparent)
  79     * (equal? true (equal? (a 'b) (a 'b)))
  80     * (define b (a b))
  81     * (equal? true (equal? b b))
  82     * all structures in book are transparent
  83 **** checkpoint
  84      * basic data: booleans, symbols, numbers, strings
  85      * lists
  86      * structs
  87      * nesting of lists and structs