this creates a structure
* fields: name, id#, dorm
* (equal? (student-name freshman1) 'Joe)
+*** nesting structures
+ * (struct student-body (freshmen sophomores juniors seniors))
+ * (define all-student (list a b) (list) (list c d) (list e))
+ * a b c d e can all be student struct instances
+ * nested selectors:
+ * (student-name (first (student-body-freshmen all-students)))
+*** structure transparency
+ * default is opaque
+ * opaque means comparison is by identity not value
+ * (equal? false (equal? (student 'joe 1 'dorm) (student 'joe 1 'dorm)))
+ * (equal? true (equal? freshman1 freshman1))
+ * transparent structs are compared on value
+ * create transparent struct type: (struct a (b) #:transparent)
+ * (equal? true (equal? (a 'b) (a 'b)))
+ * (define b (a b))
+ * (equal? true (equal? b b))
+ * all structures in book are transparent
+**** checkpoint
+ * basic data: booleans, symbols, numbers, strings
+ * lists
+ * structs
+ * nesting of lists and structs
+** conditions and decisions
+*** how to ask
+ * predicates are questions
+ * #t true, and #f false
+ * predicate is a function that returns true or false
+ * zero? symbol=? symbol? student?
+ * doing something like (zero? "asdf") will give an error, not false
+ * real? number? string? list? cons? empty? rational? exact-integer?
+ * equal? compares everything. still gives error if you give wrong arity
+ * the predicate indicates what kind of arguments it works on
+*** the conditionals: if and beyond
+ * (equal? 'yup (if (= (+ 1 2) 3) 'yup 'nope))
+ * invented in 1960s by john mccarthy
+ * #f is false and everything else is true, including '()
+ * examples
+ * (if '(1) 'consequent 'alternative) 'consequent
+ * (if '() 'consequent 'alternative) 'consequent
+ * (if #f 'consequent 'alternative) 'alternative
+ * ((if 'a
+ (display "consequent")
+ (display "alternative"))) ;; prints "consequent"
projects / ozzloy@gmail.com / realm-of-racket-journey / blobdiff