| 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 |
| 88 | ** 4 conditions and decisions |
| 89 | *** 4.1 how to ask |
| 90 | * predicates are questions |
| 91 | * #t true, and #f false |
| 92 | * predicate is a function that returns true or false |
| 93 | * zero? symbol=? symbol? student? |
| 94 | * doing something like (zero? "asdf") will give an error, not false |
| 95 | * real? number? string? list? cons? empty? rational? exact-integer? |
| 96 | * equal? compares everything. still gives error if you give wrong arity |
| 97 | * the predicate indicates what kind of arguments it works on |
| 98 | *** 4.2 the conditionals: if and beyond |
| 99 | * (equal? 'yup (if (= (+ 1 2) 3) 'yup 'nope)) |
| 100 | * invented in 1960s by john mccarthy |
| 101 | * #f is false and everything else is true, including '() |
| 102 | * examples |
| 103 | * (if '(1) 'consequent 'alternative) 'consequent |
| 104 | * (if '() 'consequent 'alternative) 'consequent |
| 105 | * (if #f 'consequent 'alternative) 'alternative |
| 106 | * (if (display "condition") |
| 107 | (display "consequent") |
| 108 | (display "alternative")) ;; prints "conditionconsequent" |
| 109 | * cond is like if else-if else-if ... |
| 110 | * (cond [condition0 consequent0] [condition1 consequent1] [else default]) |
| 111 | **** a first taste of recursion |
| 112 | * (define (my-length a-list) |
| 113 | (if (empty? a-list) |
| 114 | 0 |
| 115 | (add1 (my-length (rest a-list))))) |
| 116 | * this is called a "list-eater" |
| 117 | *** 4.3 cool tricks with conditionals |
| 118 | **** using the stealth conditionals AND and OR |
| 119 | * AKA short-circuiting conditionals |
| 120 | * (if file-modified |
| 121 | (if (ask-user-about-saving) |
| 122 | (save-file) |
| 123 | false) |
| 124 | false) |
| 125 | * (and file-modified (ask-user-about-saving) (save-file)) |
| 126 | * (when (and file-modified (ask-user-about-saving)) |
| 127 | (save-file)) |
| 128 | * unless is when with not. (unless condition action) |
| 129 | **** using functions that return more than just the truth |
| 130 | * (member 1 '(1 2)) ;; '(1 2) |
| 131 | * (member 2 '(1 2)) ;; '(2) |
| 132 | *** 4.4 equality predicates, once more |
| 133 | * (struct point (x y) #:transparent) |
| 134 | * point point-x point-y point? |
| 135 | * (define (distance-to-origin p) |
| 136 | (sqrt (+ (sqr (point-x p)) (sqr (point-y p))))) |
| 137 | * (distance-to-origin (point 3 4)) |
| 138 | * give names to points using define: |
| 139 | * (define pt1 (point -1 2)) |
| 140 | * (define pt2 (point -1 2)) |
| 141 | * equal? checks equality of all components of a struct |
| 142 | * (equal? pt1 pt2) |
| 143 | * how would you write equal? |
| 144 | * (define (my-equal? a b) |
| 145 | (cond |
| 146 | [(and (point? a) (point? b)) |
| 147 | (and (my-equal? (point-x a) (point-x b)) |
| 148 | (my-equal? (point-y a) (point-y b)))] ... )) |
| 149 | * you need another cond clause for every struct, and primitive forms |
| 150 | of data, like boolean, numbers, strings |
| 151 | * whenever a new struct is added, equal? definition must be updated |
| 152 | * to compare whether two concrete structures are the same piece of |
| 153 | memory, use eq? |
| 154 | * (eq? pt1 pt2) #f |
| 155 | * (eq? pt1 pt1) #t |
| 156 | * construct a scenario where (eq? a b) evaluates to #t |
| 157 | * you can give new names to existing values with define |
| 158 | * (define pt3 pt1) |
| 159 | * construct a scenario where (eq? a b) evaluates to #t |
| 160 | * do not use define to give a new name to a value |
| 161 | * (define (eq-first-items list1 list2) |
| 162 | (eq? (first list1) (first list2))) |
| 163 | * (eq-first-items (cons pt1 empty) (cons pt3 empty)) |
| 164 | * equal? checks if things are made of equal values |
| 165 | * eq? checks whether two names refer to the same exact thing |
| 166 | *** 4.5 comparing and testing |
| 167 | * write tests before writing functions |
| 168 | * test is function call and expected result value |
| 169 | * racket compares return value with expected |
| 170 | * if dissimilar, test or function or both are wrong |
| 171 | * (require rackunit) |
| 172 | **** writing a test |
| 173 | * check-equal? is most common |
| 174 | * (check-equal? (add1 5) 6) |
| 175 | * says nothing if test passes |
| 176 | * throws failure if test fails |
| 177 | * (check-equal? (add1 5) 7) |
| 178 | **** what is not a test |
| 179 | * running a function or program by hand is not a test |
| 180 | * though it's ok to explore a function by hand |
| 181 | * writing down expectation afterwards |
| 182 | * no automatic comparison |
| 183 | **** testing in the real world |
| 184 | * tests take an optional 3rd argument string to clarify |
| 185 | * (check-equal? 5 6 "numbers matter") |
| 186 | * check-not-equal? check-pred check-= check-true check-false |
| 187 | **** call-with-current-continuation - chapter checkpoint pp 70 |
| 188 | * racket has predicates of type and equality |
| 189 | * if and cond are the most important conditionals |
| 190 | ** 4-and-a-half (define define 'define) |
| 191 | *** 4-and-a-half.1 module level definitions |
| 192 | * most common kind of definitions are module-level |
| 193 | * introduce names that can be accessed anywhere in the module |
| 194 | * think of module as definitions panel |
| 195 | * variable and function definitions |