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
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
|
; Unions
; Todo:
; - finish the code below
; - add this file to the packages
; - add a separate field and member resolution phase.
; - figure out how union literals are going to work
; - to-cps method for type-case
; - C generation methods for unions, union literals, type-case, and
; x->type (which is a cast).
; Plan - datatypes with the initial restriction that a datatype
; cannot be polymorphic (does this matter?) and cannot have more than one
; non-nullary constructor. What is needed is a new expander and a couple
; of primitives:
;
; (x->union value 'union-type 'variant)
; (type-case value 'union-type '(variant ...) . conts)
;
; X->UNION does type checking and is a no-op in C.
; TYPE-CASE does type checking (VALUE must have type UNION-TYPE and the
; continuations receive arguments of the type of the corresponding variant).
; The C code does a switch for the nullary constructors and a second switch
; using the type field of the non-nullary constructors. Not every type
; needs both switches.
; Representation of union types.
(define-record-type union-type :union-type
(really-make-union-type name)
union-type?
(name union-type-name)
; MEMBERS are filled in later because of circularity
(members union-type-members set-union-type-members))
(define-union-discloser :union-type
(lambda (rtype)
(list 'union-type (union-type-name rtype))))
; Members of union types.
(define-record-type union-member :union-member
(make-union-member union-type name type)
union-member?
(union-type union-member-union-type)
(name union-member-name)
(type union-member-type))
; Global table of union types. Since we compile to a single C file the
; union types used within a single computation must have distinct names.
; (This should really be a fluid.)
(define *union-type-table* (make-symbol-table))
(define (reset-union-data!)
(set! *union-type-table* (make-symbol-table)))
(define (get-union-type id)
(cond ((table-ref *union-type-table* id)
=> identity)
(else
(error "no union type ~S" id))))
(define (lookup-union-type id)
(table-ref *union-type-table* id))
(define (all-union-types)
(table->entry-list *union-type-table*))
; Construction a union type. This gets the name and the member specifications.
; Each member specification consists of a name and a type.
; Aargh. What to do? The simplest thing might be to expand define-data-type
; into define-record-types and and a define-union-type. Except that we hit
; the circularity problem again. We need to create record field type after
; all macro expansion has been completed.
(define (make-union-type id specs)
(let ((ut (really-make-union-type id)))
(if (table-ref *union-type-table* id)
(user-error "multiple definitions of union type ~S" id))
(table-set! *union-type-table* id ut)
(set-union-type-members! ut (map (lambda (spec)
(make-union-member
ut
(car spec)
(expand-type-spec (cadr spec))))
specs))
(set-union-type-constructor-args! ut
(map (lambda (name)
(get-union-type-member id name))
constructor-args))
ut))
; Return the member record for MEMBER-ID in union-type TYPE-ID.
(define (get-union-type-member type-id member-id)
(let ((utype (get-union-type type-id)))
(cond ((any (lambda (member)
(eq? member-id (union-member-name member)))
(union-type-members utype))
=> identity)
(else
(user-error "~S is not a member of ~S" member-id utype)))))
; Returns a list of the expected continuation types (each of which returns
; UVAR) as its result.
(define (get-union-deconstruction-types type-id uvar)
...)
;(define-data-type list delistifier
; (pair :pair pair->list
; (make-pair car cdr)
; (car integer car set-car!)
; (cdr list cdr set-cdr!))
; (null))
;
; ->
;
; (define-record-type pair :pair
; (make-pair car cdr)
; (car integer car set-car!)
; (cdr list cdr set-cdr!))
; (define-union-type list delistifier
; (pair :pair pair->list) ; must be a record type
; (null)) ; implied unit type
; (define-union-type list delistifier
; (pair :pair)
; null) ; implied unit type
; ->
; (define (pair->list x) (x->union x 'list 'pair))
; (define null (x->union 0 'list 'null)) ; needs compile-time objects
; (define (delistifier x pair-cont null-cont)
; (type-case x 'list '(pair null) pair-cont null-cont))
(define (expand-union-type exp r c)
(let ((id (cadr exp))
(deconstructor (caddr exp))
(members (cdddr exp)))
(let* ((ut (make-union-type id members))
(conts (make-names members r)))
`(,(r 'begin)
(,(r 'define) (,deconstructor ,(r 'x) . ,conts)
(,(r 'type-case) ,(r 'x) ',id . ,conts))
. ,(apply append
(do ((members members (cdr members))
(i 0 (+ i 1))
(res '() (cons (expand-member (car members) i id r)
res)))
((null? members)
(apply append (reverse res)))))))))
; MEMBER is either (tag-name type injector-name) or just the tag-name.
(define (expand-member member i type-id r)
(if (pair? member)
`((,(r 'define) (,(caddr member) ,(r 'x))
(,(r 'x->union) ,(r 'x) ',type-id ',(car member))))
`((,(r 'define) ,member
(,(r 'x->union) ,i ',type-id ',member)))))
(define (make-names things r)
(do ((i 0 (+ i 1))
(things things (cdr things))
(names '() (cons (r (build-symbol 'c i))
names)))
(reverse names)))
(define (build-symbol . args)
(string->symbol
(string-append (map (lambda (x)
(cond ((string? x)
x)
((symbol? x)
(symbol->string x))
((number? x)
(number->string x))
(else
(error "can't coerce to string" x))))
args))))
;(define (expand-define-data-type exp r c)
; (let ((id (cadr exp))
; (deconstructor (caddr exp))
; (options (cdddr exp)))
; (let* ((specs (map (lambda (option)
; (if (null? (cdr option))
; option
; (cons (car option)
; (map car (cddddr option)))))
; options))
; (dt (make-union-type id specs))
; (conts (make-names specs r)))
; `(,(r 'begin)
; (,(r 'define) (,deconstructor ,(r 'x) . ,conts)
; (,(r 'type-case) ,(r 'x) ',id . ,conts))
; . ,(apply append
; (do ((options options (cdr options))
; (i 0 (+ i 1))
; (res '() (cons (expand-option (car options) i id r)
; res)))
; ((null? options)
; (apply append (reverse res)))))))))
;
;(define (expand-option option i type-id r)
; (if (null? (cdr option))
; `((,(r 'define) (,(car option))
; (,(r 'x->union) ,i ',type-id ',(car option))))
; `((,(r 'define-record-type) ,(car option)
; ,(cadr option)
; . ,(cdddr option))
; (,(r 'define) (,(caddr option) ,(r 'x))
; (,(r 'x->union) ,(r 'x) ',type-id ',(car option))))))
; I'll live without this for now.
;
;(define-syntax delistify
; (syntax-rules ()
; ((delistify value . clauses)
; (really-delistify value clauses #f match-error #f match-error))))
;
;(define-syntax really-delistify
; (syntax-rules ()
; ((really-delistify value () pair? pair-cont null? null-cont)
; (delistifier value pair-cont null-cont))
; ((really-delistify value
; (((pair car-var cdr-var) code . more-code)
; . more-clauses)
; #f pair-cont null? null-cont)
; (really-delistify value
; more-clauses
; #t
; (lambda (a-pair)
; (let ((car-var (car a-pair)) ; could check for #F
; (cdr-var (cdr a-pair)))
; code . more-code))
; null?
; null-cont))
; ((really-delistify value
; (((pair . pair-var) code . more-code)
; . more-clauses)
; #f pair-cont null? null-cont)
; (really-delistify value
; more-clauses
; #t
; (lambda (pair-var)
; code . more-code)
; null?
; null-cont))
; ((really-delistify value
; (((null) code . more-code)
; . more-clauses)
; pair? pair-cont #f null-cont)
; (really-delistify value
; more-clauses
; pair?
; pair-cont
; #t
; (lambda ()
; code . more-code)))
; (error)))
|
