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 + * / Ð))
math-functions
? math-functions
({method +} {method *} {method /} {method Ð})
? (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) ((cÊ<mutable-sequence>)
(keyÊ<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