1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
|
; Part of Scheme 48 1.9. See file COPYING for notices and license.
; Authors: Richard Kelsey, Jonathan Rees
; Finite types (i.e. record types with a fixed set of elements).
;
; An enumeration is really a special case of a finite type.
;
; (define-finite-type <id and dispatch-macro>
; <type name>
; (<constructor field name> ...)
; <predicate>
; <vector of elements>
; <name accessor>
; <index accessor>
; (<field name> <field accessor> [<field setter>])
; ...
; ((<element name> <constructor field value> ...)
; ...))
;
; This is equivalent to
;
; (define-record-type <id and dispatch-macro>
; <type name>
; (maker name index <constructor field name> ...)
; <predicate>
; (name <name accessor>)
; (index <index accessor>)
; (<field name> <field accessor> [<field setter>])
; ...)
;
; (define <vector of elements>
; (vector (maker <element name> 0 <constructor field value>)
; (maker <element name> 1 <constructor field value>)
; ...))
;
; (define-dispatch-macro <id and dispatch-macro>
; (<element name> ...)
; <vector-of-elements>)
;
; where DEFINE-DISPATCH-MACRO defines an ENUM-like dispatcher.
;
;(define-finite-type foo :foo ; id and type
; foo? ; predicate
; foo-elements ; vector containing all elements
; foo-name ; name accessor
; foo-index ; index accessor
; (color foo-color set-foo-color!) ; any additional fields
; ((name color) ; element pattern
; (a 'red) ; the elements themselves
; (b 'green)
; (c 'puce)
; (d 'taupe)))
;
; (foo a) -> #{foo a}
(define-syntax define-finite-type
(lambda (form rename compare)
(let ((destruct (lambda (proc)
(apply proc (cdr form))))
(%define-record-type (rename 'define-record-type))
(%define-record-discloser (rename 'define-record-discloser))
(%define (rename 'define))
(%begin (rename 'begin))
(%lambda (rename 'lambda))
(%vector (rename 'vector))
(%list (rename 'list))
(%define-dispatch (rename 'define-dispatch))
(%make-immutable! (rename 'make-immutable!))
(%maker (rename 'maker))
(%name (rename 'name))
(%index (rename 'index))
(%blah (rename 'blah)))
(destruct (lambda (foo :foo pattern foo? foo-elements foo-name foo-index
. more)
(let* ((fields (do ((more more (cdr more))
(fields '() (cons (car more) fields)))
((or (null? more)
(pair? (caar more)))
(reverse fields))))
(elts (car (reverse more)))
(names (map car elts)))
`(,%begin
(,%define-record-type ,foo ,:foo
(,%maker ,%name ,%index . ,pattern)
,foo?
(,%name ,foo-name)
(,%index ,foo-index)
. ,fields)
(,%define-record-discloser ,:foo
(,%lambda (,%blah)
(,%list ',foo (,foo-name ,%blah))))
(,%define ,foo-elements
(,%make-immutable!
(,%vector . ,(do ((elts elts (cdr elts))
(i 0 (+ i 1))
(res '() `((,%maker ',(caar elts)
,i
. ,(cdar elts))
. ,res)))
((null? elts)
(reverse res))))))
(,%define-dispatch ,foo ,names ,foo-elements)))))))
(define-record-type define-record-discloser define-dispatch
define begin lambda vector list))
; (define-dispatch <name> (<member name> ...) <vector of members>)
;
; This defines <name> to be a macro (<name> X) that looks X up in
; the list of member names and returns the corresponding element of
; <vector of members>.
;
; (define-dispatch foo (a b c) members)
; (foo b) -expands-into-> (vector-ref members 1)
(define-syntax define-dispatch
(lambda (form0 rename0 compare0)
(let ((name (cadr form0))
(names (caddr form0))
(elts (cadddr form0))
(%vector-ref (rename0 'vector-ref))
(%code-quote (rename0 'code-quote)))
`(define-syntax ,name
(lambda (form1 rename1 compare1)
(let ((elt (cadr form1)))
(let loop ((names ',names) (i 0))
(cond ((null? names)
form1)
((compare1 elt (car names))
(list (,%code-quote ,%vector-ref) (rename1 ',elts) i))
(else
(loop (cdr names) (+ i 1))))))))))
(vector-ref code-quote))
; (define-enumerated-type <id and dispatch-macro>
; <type name>
; <predicate>
; <vector of elements>
; <name accessor>
; <index accessor>
; (<element name> ...))
;
; This is a simplified version that has no additional fields. It avoids
; a lot of unnecessary parens around the element names.
;
; The above expands into:
;
; (define-finite-type <id and dispatch-macro>
; <type name>
; <predicate>
; <vector of elements>
; <name accessor>
; <index accessor>
; ((name)
; (<element name>)
; ...))
(define-syntax define-enumerated-type
(syntax-rules ()
((define-enumerated-type id type-name predicate elements
name-accessor index-accessor
(element ...))
(define-finite-type id type-name () predicate elements
name-accessor index-accessor
((element) ...)))))
|
