This document contains the examples from "Dylan: an object-oriented dynamic
language".

copyright 1992, Apple Computer



Page 27

   ? "abc"
   "abc"
   ? 123
   123
   ? foo:
   foo:
   ? #\a
   #\a
   ? #t
   #t
   ? #f
   #f
   ? (quote foo)
   foo
   ? 'foo
   foo
   ? '(1 2 3)
   (1 2 3)


Page 28-29

   ? <window>
   {the class <window>}
   ? concatenate
   {the generic function concatenate}
   ? (define my-variable 25)
   my-variable
   ? my-variable
   25
   ? (bind ((x 50))
       (+ x x))
   100
   ? (setter element)
   {the generic function (setter element)}
   ? (define (setter my-variable) 20) 
   (setter my-variable)
   ? (setter my-variable)
   20

Page 29

   ? (+ 3 4)
   7
   ? (* my-variable 3)
   75
   ? (* (+ 3 4) 5)
   35
   ? ((if #t + *) 4 5)
   9

Page 30

   ; Creates and initializes a module variable
   (define my-variable 25)
   ; Sets the value to 12
   (set! my-variable 12)
   ; Returns 30. Uses lexical variables x and y.
   (bind ((x 10) (y 20))
      (+ x y))
   ; Creates an anonymous method, which expects 2 
   ; numeric arguments.
   (method ((a <number>) (b <number>))
      (list (- a b) (+ a b)))

Page 30

   ? (values 1 2 3)
   1
   2
   3
   ? (define-method edges ((center <number>)(radius <number>))
       (values (- center radius) (+ center radius)))
   edges
   ? (edges 100 2)
   98
   102

Page 32

   ? foo
   error: unbound variable foo
   ? (define foo 10)
   foo
   ? foo
   10
   ? (+ foo 100)
   110
   ? bar
   error: unbound variable bar
   ? (define bar foo)
   bar
   ? bar
   10
   ? (define foo 20)
   warning: redefining variable foo
   ? foo
   20
   ? bar
   10
   ? (+ foo bar)
   30

Page 33

   ? (bind ((number1 20))
            (number2 30))
       (+ number1 number2))
   50

Page 33

   ? (bind ((x 20)
            (y (+ x x)))
       (+ y y))
   80

Page 33

   ? (define foo 10)
   foo
   ? (+ foo foo)
   20
   ? (bind ((foo 35))
       (+ foo foo))
   70
   ? (bind ((foo 20))
       (bind ((foo 50))
         (+ foo foo)))
   100

Page 34

   ? (bind (((x <integer>) (sqrt 2)))
           x)
   error: 1.4142135623730951 is not an instance of <integer>


Page 34

   ? (bind ((foo bar baz (values 1 2 3)))
       (list foo bar baz))
   (1 2 3)
   ? (define-method opposite-edges ((center <number>)
                                    (radius <number>))
       (bind ((min max (edges center radius)))
         (values max min)))
   opposite-edges
   ? (opposite-edges 100 2)
   102
   98

Page 34

   ? (bind ((x 10)
            (y 20))
       (bind ((x y (values y x)))
         (list x y)))
   (20 10)

Page 34

   ? (bind ((#rest nums (edges 100 2)))
       nums)
   (98 102)

Page 41

   ? (double 10)
   error: unbound variable double.

Page 41

   ? (define-method double ((thing <number>))
       (+ thing thing))
   double
   ? double
   {the generic function double}
   ? (double 10)
   20

Page 41

   ? (double "the rain in Spain.")
   error: no method for {the generic function double} was found
          for the arguments ("the rain in Spain.")

Page 41

   ? (define-method double ((thing <sequence>))
       (concatenate thing thing))
   double
   ? (double "the rain in Spain.")
   "the rain in Spain.the rain in Spain."
   ? (double '(a b c))
   (a b c a b c)

Page 43

   ? (define-method show-rest (a #rest b)
       (print a)
       (print b)
       #t)
   show-rest
   ? (show-rest 10 20 30 40)
   10
   (20 30 40)
   #t
   ? (show-rest 10)
   10
   ()
   #t

Page 44

   (define-method percolate (#key (brand 'maxwell-house)
                                  (cups 4)
                                  (strength 'strong))
     (make-coffee brand cups strength))
   (define-method layout (widget #key (position: the-pos)
                                      (size: the-size))
     (bind ((the-sibling (sibling widget)))
      (unless (= the-pos (position the-sibling))
        (align-objects widget the-sibling the-pos the-size))

Page 44

   (percolate brand: 'folgers cups: 10)
   (percolate strength: 'weak
              brand: 'tasters-choice
              cups: 1)
   (layout my-widget position: (point 10 10)
                     size: (point 30 50))
   (layout my-widget size: (query-user-for-size))

Page 45

   ? (define-method show-keys (req1 req2 #key foo)
       (format #t "requireds: ~a ~a~%" req1 req2)
       (format #t "key: ~a" foo)
       #t)
   show-keys
   ? (show-keys 'one 'two foo: 'three)
   requireds: one two
   key: three
   #t
   ? (show-keys foo: 'three)
   requireds: foo: three
   key: #f
   #t

Page 46

   ? (define-method label ((x <object>) #key price)
      (list price x))
   label
   ? (define-method label ((x <sequence>) #key unit-price)
      (add x (* unit-price (length x))))
   label
   ? (define-method label ((x <list>) #rest info #key calories)
      (add x calories))
   label
   ? (label 'grape price: 189 unit-price: 2)
   error:  illegal keyword argument unit-price:.  Accepted keyword arguments are (price:).
   ? (label 'grape price: 189)
   (189 grape)
   ? (label (vector 3 4 5) price: 189 unit-price: 2)
   #(6 3 4 5)
   ? (label (vector 3 4 5) protein: 7 fat: 8 calories: 9)
   error:  illegal keyword argument protein:.  Accepted keyword arguments are (price: unit-price:).
   ? (label (list 3 4 5) protein: 7 fat: 8 calories: 9)
   (9 3 4 5)

Page 46

   ? (define-method test (the-req #rest the-rest
                                  #key a b)
       (print the-req)
       (print the-rest)
       (print a)
       (print b))
   test
   ? (test 1 a: 2 b: 3 c: 4)
   1
   (a: 2 b: 3 c: 4)
   2
   3

Page 49

   (define-class <point> (<object>)
     horizontal
     vertical)

Page 49

   (horizontal my-point)

Page 49

   ((setter horizontal) my-point 10)

Page 50

   (set! (horizontal my-point) 10)

Page 51   
   
   ? (define-class <menu> (<object>)
       title
       action)

Page 55

   ? (define-class <rectangle> (<object>)
        (top type: <integer>
             init-value: 0
             init-keyword: top:)
        (left type: <integer>
              init-value: 0
              init-keyword: left:)
        (bottom type: <integer>
                init-value: 100
                init-keyword: bottom:)
        (right type: <integer>
               init-value: 100
               init-keyword: right:))
   <rectangle>
   ? <rectangle>
   {the class <rectangle>}
   ? (define my-rectangle (make <rectangle> top: 50 left: 50))
   my-rectangle
   ? (top my-rectangle)
   50
   ? (bottom my-rectangle)
   100
   ? (set! (bottom my-rectangle) 55)
   55
   ? (bottom my-rectangle)
   55
   ? (set! (bottom my-rectangle) 'foo)
   error: foo is not an instance of <integer> while executing (setter bottom).


Page 58
   
   (define-class <view> (<object>)
     (position allocation: instance)
     ...)
   
   (define-class <displaced-view> (<view>)
     (position allocation: virtual)
     ...)
   
   (define-method position ((v <displaced-view>))
     (displace-transform (next-method v)))
   
   (define-method (setter position) ((v <displaced-view>)
                                     new-position)
     (next-method v (undisplace-transform new-position)))

Page 59

   (define-class <shape> (<view>)
     (image allocation: virtual)
     (cached-image allocation: instance init-value: #f)
     ...)
   
   (define-method image ((shape <shape>))
     (or (cached-image shape)
         (set! (cached-image shape) (compute-image shape))))
   
   (define-method (setter image) ((shape <shape>) new-image)
     (set! (cached-image shape) new-image))

Page 61

   ? (define foo 10)
   10
   ? foo             ;this is a variable
   10                ;this is the variableÕs contents
   ? (set! foo (+ 10 10))
   20
   ? foo
   20
   ? (setter element)                   ;this is a variable
   {generic function (setter element)}  ;the variableÕs contents
   ? (set! (setter element) %set-element)
   {primitive function %set-element}
   ? (id? (setter element) %set-element)
   #t

Page 62

   ? (define foo (vector 'a 'b 'c 'd))
   foo
   ? foo
   #(a b c d)
   ? (element foo 2)
   c
   ? (set! (element foo 2) 'sea)
   sea
   ? (element foo 2)
   sea
   ? foo
   #(a b sea d)

Page 64

   ? (define-method test ((thing <object>))
       (if thing
           #t
           #f))
   test
   ? (test 'hello)
   #t
   ? (test #t)
   #t
   ? (test #f)
   #f
   
   ? (define-method double-negative ((num <number>))
        (if (< num 0)
            (+ num num)
            num))
   double-negative
   ? (double-negative 11)
   11
   ? (double-negative -11)
   -22

Page 65

   ? (define-method show-and-tell ((thing <object>))
        (if thing
            (begin
               (print thing)
               #t)
            #f))
   show-and-tell
   ? (show-and-tell "hello")
   hello
   #t

Page 65

   (when (bonus-illuminated? pinball post)
       (add-bonus-score current-player 100000))

Page 65

   (unless (detect-gas? nose)
       (light match))

Page 66
   
   (cond ((< new-position old-position)
            "the new position is less")
          ((= new-position old-position)
           "the positions are equal")
          (else: "the new position is greater"))

Page 67

   (case (career-choice student)
      ((art music drama)
       (print "DonÕt quit your day job."))
      ((literature history linguistics)
       (print "That really is fascinating."))
      ((science math engineering)
       (print "Say, can you fix my VCR?"))
      (else: "I wish you luck."))

Page 67

   (select my-object instance?
     ((<window> <view> <rectangle>) "itÕs a graphic object")
     ((<number> <list> <sequence>) "itÕs something computational")
     (else: "DonÕt know what it is"))

Page 68

   ? (if #t
         (print "it was true")
         #t
         #f)
   error:  too many arguments to if.
   ? (if #t
         (begin (print "it was true")
                #t)
         #f)
   "it was true"
   #t

Page 69

   (define-method factorial ((n <integer>))
      (for ((i n (- i 1))   ;variable clause 1
            (v 1 (* v i)))  ;variable clause 2
           ((<= i 0) v))    ;end test and result

Page 69

   (define-method first-even ((s <sequence>))
     (for-each ((number s))
               ((even? number) number)
                                ; No body forms needed
        ))

Page 70

   (define-method schedule-olympic-games ((cities <sequence>)
                                          (start-year <number>))
      (for-each ((year (range from: start-year by: 4))
                 (city cities))
                ()              ; No end test needed.
         (schedule-game city year)))

Page 70

   ? (begin
       (dotimes (i 6) (print "bang!"))
       (print "click!"))
   bang!
   bang!
   bang!
   bang!
   bang!
   bang!
   click!

Page 71

   ? (define-method first-even ((seq <sequence>))
       (bind-exit (exit)
         (do (method (item)
                (when (even? item)
                  (exit item)))
              seq)))
   first-even
   ? (first-even '(1 3 5 4 7 9 10))
   4

Page 72

   ? +
   {the generic function +}
   ? '+
   +
   ? (quote +)
   +
   ? ''+
   (quote +)
   ? (+ 10 10)
   20
   ? '(+ 10 10)
   (+ 10 10)
   ? (quote (+ 10 10))
   (+ 10 10)

Page 73

   ? (apply + 1 '(2 3))
   6
   ? (+ 1 2 3)
   6
   ? (define math-functions (list + * / Š))
   math-functions
   ? math-functions
   ({method +} {method *} {method /} {method Š})
   ? (first math-functions)
   {method +}
   ? (apply (first math-functions) 1 2 '(3 4))
   10

Page 79

   ? (method (num1 num2)
       (+ num1 num2))
   {an anonymous method}

Page 80

   ;the second argument to SORT is the test function
   ? (sort person-list
           (method (person1 person2)
             (< (age person1)
                (age person2))))
   ? (bind ((double (method (number)
                      (+ number number))))
       (double (double 10)))
   40

Page 80

   ? (define-method double ((my-method <function>))
       (method (#rest args)
         (apply my-method args)
         (apply my-method args)
         #f))
   double
   ? (define print-twice (double print))
   print-twice
   ? print-twice
   {an anonymous method}
   ? (print-twice "The rain in Spain. . .")
   The rain in Spain. . .The rain in Spain. . .
   #f
   ? (print-twice 55)
   5555
   #f

Page 81

   ? (define-method root-mean-square ((s <sequence>))
        (bind-methods ((average (numbers)
                         (/ (reduce1 + numbers)
                            (length numbers)))
                       (square (n) (* n n)))
           (sqrt (average (map square s)))))
   root-mean-square
   ? (root-mean-square '(5 6 6 7 4))
   5.692099788303083

Page 81

   ? (define-method newtons-sqrt (x)
        (bind-methods ((sqrt1 (guess)
                          (if (close? guess) 
                              guess 
                              (sqrt1 (improve guess))))
                       (close? (guess)
                          (< (abs (- (* guess guess) x)) .0001))
                       (improve (guess)
                          (/ (+ guess (/ x guess)) 2)))
               (sqrt1 1)))
   newtons-sqrt
   ? (newtons-sqrt 25)
   5.000000000053723

Page 82

   ? (define-method double ((thing <number>))
       (+ thing thing))
   double

Page 82

   ? (double 10)
   20
   ? (double 4.5)
   9.0

Page 82

   ? (define-method double ((thing <integer>))
       (* thing 2))
   double

Page 82

   ? (define-method double ((thing (singleton 'cup)))
       'pint)
   double
   ? (double 'cup)
   pint

Page 83

   ? (define-method double ((num <float>))
       (print "doubling a floating-point number")
       (next-method))
   double
   ? (double 10.5)
   doubling a floating-point number
   21.0

Page 85

   (define-method show ((device <window>) (thing <character>))
     ...)
   
   (define-method show ((device <window>) (thing <string>))
     ...)
   
   (define-method show ((device <window>) (thing <rectangle>))
     . . .)
   
   (define-method show ((device <file>) (thing <character>))
     . . .)
   
   (define-method show ((device <file>) (thing <string>))
     . . .)

Page 86

   ? (make <generic-function> required: 3)
   {an anonymous generic function}
   ? (make <generic-function> required: 3
                              debug-name: 'foo)
   {the generic function foo}
   ? (define expand
       (make <generic-function> required: 1 debug-name: 'expand))
   {the generic function expand}
   ? (expand 55)
   error: no applicable method for 55 in {the generic function expand}

Page 97

   ? (define-method double ((thing (singleton 'cup)))
       'pint)
   double
   ? (double 'cup)
   pint
   ? (double 10)
   20

Page 98

   ? (define-method factorial ((num <integer>))
       (* num (factorial (- num 1))))
   factorial
   ? (define-method factorial ((num (singleton 0)))
        1)
   factorial
   ? (factorial 5)
   120

Page 100

   ? (do (method (a b) (print (+ a b)))
         '(100 100 200 200)
         '(1 2 3 4))
   101
   102
   203
   204
   #f

Page 101

   ? (map +
         '(100 100 200 200)
         '(1 2 3 4))
   (101 102 203 204)

Page 101

   ? (map-as <vector> +
         '(100 100 200 200)
         '(1 2 3 4))
   #(101 102 203 204)

Page 101

   ? (define x '(100 100 200 200))
   x
   ? (map-into x + '(1 2 3 4))
   (101 102 203 204)
   ? x
   (101 102 203 204)

Page 102

   ? (any? > '(1 2 3 4) '(5 4 3 2))
   #t
   ? (any? even? '(1 3 5 7))
   #f

Page 102

   ? (every? > '(1 2 3 4) '(5 4 3 2))
   #f
   ? (every? odd? '(1 3 5 7))
   #t

Page 102

   ? (define high-score 10)
   high-score
   ? (reduce max high-score '(3 1 4 1 5 9))
   10
   ? (reduce max high-score '(3 12 9 8 8 6))
   12

Page 103

   ? (reduce1 + '(1 2 3 4 5))
   15

Page 103

   ? (define flavors #(chocolate pistachio pumpkin))
   flavors
   ? (member? 'chocolate flavors)
   #t
   ? (member? 'banana flavors)
   #f

Page 103

   ? flavors
   (chocolate pistachio pumpkin)
   ? (find-key flavors has-nuts?)
   1
   ? (element flavors 1)
   pistachio

Page 104

? (define numbers (list 10 13 16 19))
numbers
? (replace-elements! numbers odd? double)
(10 26 16 38)

Page 104

? (define x (list 'a 'b 'c 'd 'e 'f))
x
? (fill! x 3 start: 2)
(a b 3 3 3 3)

Page 105

   ? (define numbers '(3 4 5))
   numbers
   ? (add numbers 1)
   (1 3 4 5)
   ? numbers
   (3 4 5)

Page 105

   ? (define numbers (list 3 4 5))
   numbers
   ? (add! numbers 1)
   (1 3 4 5)

Page 105

   ? (add-new '(3 4 5) 1)
   (1 3 4 5)
   ? (add-new '(3 4 5) 4)
   (3 4 5)

Page 105

   ? (add-new! (list 3 4 5) 1)
   (1 3 4 5)
   ? (add-new! (list 3 4 5) 4)
   (3 4 5)

Page 106

   ? (remove '(3 1 4 1 5 9) 1)
   (3 4 5 9)

Page 106

   ? (remove! (list 3 1 4 1 5 9) 1)
   (3 4 5 9)

Page 106

   ? (choose even? '(3 1 4 1 5 9))
   (4)

Page 106

   ? (choose-by even? (range from: 1)
                      '(a b c d e f g h i))
   (b d f h)

Page 107

   ? (intersection '(john paul george ringo)
                   '(richard george edward charles john))
   (john george)

Page 107

   ? (union '(butter flour sugar salt eggs)
            '(eggs butter mushrooms onions salt))
   (salt butter flour sugar eggs mushrooms onions)

Page 107

   ? (remove-duplicates '(spam eggs spam sausage spam spam spam))
   (spam eggs sausage)

Page 108

   ? (remove-duplicates! '(spam eggs spam sausage spam spam))
   (spam eggs sausage)
   
Page 108
   
   ? (define hamlet '(to be or not to be))
   hamlet
   ? (id? hamlet (copy-sequence hamlet))
   #f
   ? (copy-sequence hamlet start: 2 end: 4)
   (or not)

Page 108

   ? (concatenate-as <string> '(#\n #\o #\n) '(#\f #\a #\t))
   "nonfat"
   ? (concatenate-as <vector> '(0 1 2) '(3 4 5) '(6 7 8))
   #(0 1 2 3 4 5 6 7 8)

Page 108

   ? (concatenate "low-" "calorie")
   "low-calorie"
   ? (concatenate '(0 1 2) '(3 4 5) '(6 7 8))
   (0 1 2 3 4 5 6 7 8)

Page 109

   ? (define phrase "I hate oatmeal.")
   phrase
   ? (replace-subsequence! phrase "like" start: 2)
   "I like oatmeal."


Page 109

   ? (define x '(bim bam boom))
   x
   ? (reverse x)
   (boom bam bim)
   ? x
   (bim bam boom)


Page 109

   ? (reverse! '(bim bam boom))
   (boom bam bim)

Page 110

   ? (define numbers '(3 1 4 1 5 9))
   numbers
   ? (sort numbers)
   (1 1 3 4 5 9)
   ? numbers
   (3 1 4 1 5 9)

Page 110

   ? (sort! '(3 1 4 1 5 9))
   (1 1 3 4 5 9)

Page 110

   ? (last '(emperor of china))
   china

Page 111

   ? (subsequence-position "Ralph Waldo Emerson" "Waldo")
   6

Page 113

   ? (aref #(7 8 9) 1)
   8

Page 113

   ? (set! (aref #(7 8 9) 1) 5)
   #(7 5 9)                        ;buggy example.  Should return 5
   ? ((setter aref) #(7 8 9) 1 5)
   #(7 5 9)                        ;buggy example.  Should return 5

Page 113

   ? (dimensions (make <array> dimensions: '(4 4)))
   (4 4)

Page 115

   ? (cons 1 2)
   (1 . 2)
   ? (cons 1 '(2 3 4 5))
   (1 2 3 4 5)

Page 115

   ? (list 1 2 3)
   (1 2 3)
   ? (list (+ 4 3) (- 4 3))
   (7 1)

Page 115

   ? (list* 1 2 3 '(4 5 6))
   (1 2 3 4 5 6)


Page 116

   ? (car '(4 5 6))
   4
   ? (car '())
   ()

Page 116

   ? (cdr '(4 5 6))
   (5 6)
   ? (cdr '())
   ()

Page 116

   ? (define x '(4 5 6))
   (4 5 6)
   ? (set! (car x) 9)
   9

Page 116

   ? (define x '(4 5 6))
   (4 5 6)
   ? (set! (cdr x) '(a b c))
   (a b c)

Page 120

   ? (define x "Van Gogh")
   x
   ? (as-lowercase x)
   "van gogh"
 
Page 120

   ? (define x "Van Gogh")
   x
   ? (as-lowercase! x)
   "van gogh"

Page 120

   ? (define x "Van Gogh")
   x
   ? (as-uppercase x)
   "VAN GOGH"

Page 120

   ? (define x "Van Gogh")
   x
   ? (as-uppercase x)
   "VAN GOGH"

Page 123

   (define-method do1 (f (c <collection>))
     (for ((state (initial-state c) (next-state c state)))
          ((not state) #f)
       (f (current-element c state))))

Page 125

   (define-method key-sequence ((c <explicit-key-collection>))
     (for ((state (initial-state c) (next-state c state))
           (keys  '()               (cons (current-key c state)
                                          keys)))
          ((not state) keys)))

Page 125

   (define-method do-with-keys (f (c <explicit-key-collection>))
     (for ((state (initial-state c) (next-state c state)))
          ((not state) #f)
       (f (current-key c state) (current-element c state))))

Page 126

   (define-method do-with-keys (f (c <sequence>))
     (for ((state (initial-state c) (next-state c state))
           (key   0                 (+ key 1)))
          ((not state) #f)
       (f key (current-element c state))))

Page 126

   (bind ((no-default (cons #f #f)))
   
    (define-method .i.element; ((c <explicit-key-collection>) key
                            #key (default no-default))
     (for ((state (initial-state c) (next-state c state)))
          ((or (not state) (= (current-key c state) key))
           (if state (current-element c state)
               (if (id? default no-default)
                   (error ...)
                   default)))))
    (define-method .i.element; ((c <sequence>) key
                            #key (default no-default))
      (for ((state (initial-state c) (next-state c state))
            (k     0                 (+ k 1)))
           ((or (not state) (= k key))
            (if state (current-element c state)
                (if (id? default no-default)
                    (error ...)
                    default))))) )

Page 128

   (define-method (setter element) ((cŹ<mutable-sequence>)
                                    (keyŹ<integer>) new-value)
     (for ((state (initial-state c) (next-state c state))
           (k     0                 (+ k 1)))
          ((or (not state) (= k key))
           (if state
               (set! (current-element c state) new-value)
               (error ...)))))

Page 128

   (define-method (setter element) ((c <mutable-explicit-key-collection>)
                                    key new-value)
     (for ((state (initial-state c) (next-state c state)))
          ((or (not state) (= (current-key c state) key))
           (if state
               (set! (current-element c state) new-value)
               (error ...)))))

Page 129

   (define-method do2 (f (c1 <collection>) (c2 <collection>))
     (bind ((keys (intersection (key-sequence c1)
                                (key-sequence c2))))
       (for ((ks (initial-state keys) (next-state keys ks)))
            ((not ks) #f)
         (bind ((key (current-element keys ks)))
           (f (element c1 key) (element c2 key))))))

Page 129

   (define-method do2 (f (c1 <sequence>) (c2 <sequence>))
     (for ((s1 (initial-state c1) (next-state c1 s1))
           (s2 (initial-state c2) (next-state c2 s2)))
          ((or (not s1) (not s2)) #f)
       (f (current-element c1 s1) (current-element c2 s2))))

Page 130

   (define-method map-into1 ((target <mutable-collection>) f
                             (source <collection>))
     (bind ((keys (intersection (key-sequence target)
                                (key-sequence source))))
       (for ((ks (initial-state keys) (next-state keys ks)))
            ((not ks) target)
         (bind ((key (current-element keys ks)))
           (set! (element target key) (f (element source key)))))))
   (define-method map-into1 ((target <mutable-sequence>) f
                             (source <sequence>))
     (for ((ss (initial-state source) (next-state source ss))
           (ts (initial-state target) (next-state target ts)))
          ((or (not ss) (not ts)) target)
       (set! (current-element target ts)
             (f (current-element source ss)))))

Page 142

   (handler-case (some-function)
     ((<type-error>) "there was a type-error")
     ((<error>) "there was an error")
     ((<warning>) "there was a warning"))

Page 144-146

   ;;; Classes such as <file-not-found> used in these examples are
   ;;; invented for the example and are not part of the specification
   ;;; This example shows minimal handling of a file-not-found error
   
   (handler-case (open "file-that-doesnt-exist")
     ((<file-not-found> condition: c
       (format *error-output* "~&The file ~A was not found."
               (file-name c))))
   
   
   ;;; This example shows how to handle a file-not-found error by
   ;;; reading a different file instead.
   (handler-bind (<file-not-found>
                    (method (condition next-handler)
                      (signal (make <try-a-different-file>
                                    file-name: "my-emergency-backup-file"))))
      (open "file-that-doesnt-exist")
     ....)
   
   (define-method open (the-file)
     (handler-case (guts-of-open the-file)
       ((<try-a-different-file>
         description: (method (stream)
                        (format stream "Read a different file instead of ~A"
                                        the-file))
         condition: restart
        (open (file-name restart)))))))
   
   (define-method guts-of-open (the-file)
     (bind ((result (operating-system-open the-file)))
       (cond ((instance? result <stream>) result)
             ((id? result +file-not-found-error-code+)
              (error (make <file-not-found> file-name: the-file)))
             ...)))
   
   (define-class <file-not-found> (<error>)
     ((file-name init-keyword: file-name:)))
   
   (define-method print ((self <file-not-found>) #key stream verbose)
     (if verbose
         (next-method)
         (format stream "The file ~A was not found" (file-name self))))
   
   (define-class <try-a-different-file> (<restart>)
     ((file-name init-keyword: file-name:)))
   
   
   ;;; This is the same example improved so the restart handler that
   ;;; reads another file can only be reached by a handler for the
   ;;; associated condition, useful if there are nested errors.
   
   (handler-bind (<file-not-found>)
                    (method (condition next-handler)
                      (signal (make <try-a-different-file>
                                    condition: condition
                                    file-name: "my-emergency-backup-file")))
     (open "file-that-doesnt-exist")
     ....)
   
   (define-method open (the-file)
     ....  (guts-of-open the-file))
   
   (define-method guts-of-open (the-file)
     (bind ((result (operating-system-open the-file)))
       (cond ((instance? result <stream>) result)
             ((id? result +file-not-found-error-code+)
              (bind ((condition (make <file-not-found> file-name: the-file)))
                (handler-case (error condition)
                  ((<try-a-different-file>
                     test: (compose (curry id? condition) restart-condition)
                    description: (method (stream)
                                   (format stream
                                     "Read a different file instead of ~A"
                                     the-file))
                    condition: restart
                   (open (file-name restart)))))))
             ...)))
   
   (define-class <file-not-found> (<error>)
     ((file-name init-keyword: file-name:)))
   
   (define-method print ((self <file-not-found>) #key stream verbose)
     (if verbose
        (next-method)
        (format stream "The file ~A was not found" (file-name self))))
   
   (define-class <try-a-different-file> (<restart>)
     ((condition init-keyword: condition: reader: restart-condition)
      (file-name init-keyword: file-name:)))

Page 153

   ? (as <symbol> "foo")
   foo
   ? (id? 'FOO (as <symbol> "Foo"))
   #t
   ? 'Foo
   foo
   ? (as <keyword> "foo")
   foo:

Page 154

   ? (as <string> 'Foo)
   "foo"
   ? (as <string> 'bar:)
   "bar"

Page 157

   ? (define-method sum ((numbers <sequence>))
         (reduce1 + numbers))
   sum
   ? (define-method square ((x <number>)) (* x x))
   square
   ? (define-method square-all ((coords <sequence>))
       (map square coords))
   square-all
   ? (define distance (compose sqrt sum square-all))
   distance
   ? (distance '(3 4 5))
   7.0710678118654755

Page 157

   ? (map female? '(michelle arnold roseanne))
   (#t #f #t)
   ? (map (complement female?) '(michelle arnold roseanne))
   (#f #t #f)

Page 158

   ? (map (curry + 1) '(3 4 5))
   (4 5 6)

Page 158

   ? (define yuppify (rcurry concatenate ", ayup"))
   yuppify
   ? (yuppify "I'm from New Hampsha")
   "I'm from New Hampsha, ayup"

Page 159

   ? ((always 1) 'x 'y 'z)
   1
   ? ((always #t) #f #f)
   #t