-
Notifications
You must be signed in to change notification settings - Fork 3
/
main.rkt
549 lines (397 loc) · 13.8 KB
/
main.rkt
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
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
#lang racket
(provide derp2-parser)
(require parser-tools/cfg-parser)
; derp2
; derp2 transforms a derp-style grammar into
; a yacc-style grammar, suitable for use
; with parser-tools/cfg-parser in Racket.
; (It may work with parser-tools/yacc, but there is no
; guarantee it won't produce shift/reduce conflicts.)
; It supports the common "regular" operations for patterns:
; (seq <pat> ...)
; (or <pat> ...)
; (opt <pat> [ <default> ])
; (rep <pat>)
; (rep+ <pat>)
; It also supports special reduction forms for patterns:
; ($--> <pat> <body>)
; where in the body:
; 1. $$ is result of pattern match
; 2. ($ n) is nth element in $$
; ($*--> <pat> ... <exp>)
; acts like ($--> (seq <pat> ...) <exp>)
; (>--> <pat> <match-clauses>)
; acts like ($--> <pat> (match $$ <match-clauses>))
; (@--> <pat> <exp>)
; acts like ($--> <pat> <exp> (apply <exp> $$))
; (cons <pat> <pat>)
; acts like seq, but with cons instead of list
; (car <pat>)
; takes the car of the result
; (cdr <pat>)
; takes the cdr of the result
; It supports repetition-with-separator forms:
; (rep/sep <pat> <pat> <bool>)
; (rep/sep+ <pat> <pat> <bool>)
; rep/sep matches <exp> <sep> ... <sep> <exp> [ <sep> ]
; where zero or more matches of <exp> are allowed.
; rep+/sep matches <exp> <sep> ... <sep> <exp> [ <sep> ]
; where at least one match of <exp> is guaranteed
; The boolean at the end determines whether an optional
; trailing separator is allowed.
; It also supports a special selective sequence form:
; #'(<qq-pat> ...) where <qq-pat> ::= #,<pat> | <pat>
; is a selective sequence, where only elements
; marked with #, are retained
; Ex: #'(#,foo bar #,baz)
; ==>
; ($--> (seq foo bar baz)
; (list ($ 1) ($ 3)))
(module impl racket
(provide desugar compile-derp-rules)
;; Helpers
; unzip/callback : (b c) list -> (b list c list -> ans) -> ans
; Unzips a list in continuation-passing style.
(define (unzip/callback lst k)
(match lst
['() (k '() '())]
[(cons (list a b) tl)
(unzip/callback tl (λ (as bs)
(k (cons a as) (cons b bs))))]))
; forces-$* : exp -> exp
; Forces the expression to be of the form ($--> (seq <exp> ...) <body>)
; Yacc-like tools need high-level rules to have this form.
(define (force-$* exp)
(match exp
[`($*--> ,pats ... ,body)
; =>
(force-$* `($--> (seq ,@pats) ,body))]
[`($--> (seq . ,exps) . ,body)
; =>
exp]
[`($--> ,pat . ,body)
; =>
`($--> (seq ,pat)
(let ([$ (λ (n) (list-ref ($ 1) n))]
[$$ ($ 1)]) . ,body))]
[`(seq . ,exps)
; =>
`($--> ,exp $$)]
[(or `(quote ,_)
(? symbol?)
(? string?)
`(rep ,_)
`(rep+ ,_)
`(or . ,_))
`($--> (seq ,exp) ($ 1))]))
; force-or : exp -> exp
; Forces the expression to be of the form (or <exp> ...)
; Yacc-like tools need the or at the top level.
(define (force-or exp)
(match exp
[`(or . ,exps) exp]
[else `(or ,exp)]))
; desugar : grammar -> grammar
; Eliminates these desugarable constructs from the grammar:
; ($*--> <pat> ... <exp>)
; (>--> <pat> <match-clauses>)
; (@--> <pat> <exp>)
; (cons <pat> <pat>)
; (car <pat>)
; (cdr <pat>)
; (rep/sep <pat> <pat> <bool>)
; (rep/sep+ <pat> <pat> <bool>)
; #'(<qq-pat> ...) where <qq-pat> ::= #,<pat> | <pat>
(define (desugar grammar)
(define added-rules '())
(define (add-rule! non-term rhs)
(set! added-rules (cons `[,non-term ,rhs] added-rules)))
; atomize! : exp -> exp
; Makes an expression a terminal on non-terminal, if it isn't one.
(define (atomize! exp)
(match exp
; Terminals:
[`(quote ,(? symbol?))
;=>
exp]
[(? symbol?)
;=>
exp]
[(? string?)
;=>
exp]
[else
;=>
(define $nt (gensym 'nt))
(add-rule! $nt exp)
$nt]))
; desugar-exp : exp -> exp
; Desugars an individual construct and its children.
(define (desugar-exp exp)
(match exp
; Terminals:
[`(quote ,(? symbol?))
;=>
exp]
[(? symbol?)
;=>
exp]
[(? string?)
;=>
exp]
; Reductions:
[`($--> ,exp . ,body)
`($--> ,(desugar-exp exp) . ,body)]
[`(@--> ,exp ,fn)
`($--> (seq ,exp) (apply ,fn ($ 1)))]
[`(>--> ,exp . ,match-clauses)
`($--> (seq ,exp) (match ($ 1) . ,match-clauses))]
[`($*--> ,exps ... ,body)
`($--> (seq ,@(map desugar-exp exps)) ,body)]
[`(cons ,exp1 ,exp2)
`($--> (seq ,(desugar-exp exp1) ,(desugar-exp exp2)) (cons ($ 1) ($ 2)))]
[`(car ,exp)
`($--> (seq ,(desugar-exp exp)) (car ($ 1)))]
[`(cdr ,exp)
`($--> (seq ,(desugar-exp exp)) (cdr ($ 1)))]
[(or `(syntax ,args) `(quasisyntax ,args))
;=>
(define (desugar-quoted exp position)
(match exp
[`(unsyntax ,exp)
`(,position ,(desugar-exp exp))]
[else
`(#f ,(desugar-exp exp))]))
(define desugared (map desugar-quoted args (for/list ([i (in-range 1 (+ 1 (length args)))]) i)))
(unzip/callback
desugared
(λ (positions exps)
(desugar-exp
`($--> (seq ,@exps)
(list ,@(map (λ (p) `($ ,p)) (filter identity positions)))))))]
; Core forms:
[`(seq . ,exps)
; =>
`(seq ,@(map desugar-exp exps))]
[`(or . ,exps)
; =>
`(or ,@(map desugar-exp exps))]
; Complex constructs:
[`(rep ,exp)
; =>
`(rep ,(desugar-exp exp))]
[`(rep+ ,exp)
; =>
`(rep+ ,(desugar-exp exp))]
; rep+/sep matches <exp> <sep> ... <sep> <exp> [ <sep> ]
; (At least one <exp> match is guaranteed.)
; This is useful for constructs like comma-separated lists.
[`(rep+/sep ,sep ,exp ,sep-tail?)
; =>
(define $exp (atomize! (desugar-exp exp)))
(define $sep (atomize! (desugar-exp sep)))
(define $rep (gensym '$rep))
(add-rule! $rep `(or ($--> (seq) '())
($--> (seq ,$sep ,$exp ,$rep)
(cons ($ 2) ($ 3)))))
(define $tail (if sep-tail?
`((opt ,$sep))
`()))
`(or
($--> (seq ,$exp) (list ($ 1)))
($--> (seq ,$exp ,$rep . ,$tail) (cons ($ 1) ($ 2))))]
; rep/sep matches <exp> <sep> ... <sep> <exp> [ <sep> ]
; (Zero or more matches of <exp> are allowed.)
[`(rep/sep ,sep ,exp ,sep-tail?)
(define $exp (atomize! (desugar-exp exp)))
(define $sep (atomize! (desugar-exp sep)))
(define $rep (gensym '$rep))
(add-rule! $rep `(or ($--> (seq) '())
($--> (seq ,$sep ,$exp ,$rep)
(cons ($ 2) ($ 3)))))
(define $tail (if sep-tail?
`((opt ,$sep))
`()))
`(or ($--> (seq) '())
($--> (seq ,$exp) (list ($ 1)))
($--> (seq ,$exp ,$rep . ,$tail) (cons ($ 1) ($ 2))))]
[`(opt ,exp ,value)
; =>
`(opt ,(desugar-exp exp) ,value)]
[`(opt ,exp)
; =>
`(opt ,(desugar-exp exp))]
[else
; =>
(error (format "could not desugar: ~a" exp))]))
(define (desugar-rule rule)
(match rule
[`[,non-term ,rhs]
`[,non-term ,(desugar-exp rhs)]]))
(define transformed-rules (map desugar-rule grammar))
(append transformed-rules added-rules))
;; compile-derp-rules : derp-grammar -> yacc-grammar
;; Transforms a derp-style grammar into a racket-style yacc grammar.
(define (compile-derp-rules rules)
(define extra-rules '())
(define (add-rule non-term exp)
(set! extra-rules (cons `[,non-term ,exp] extra-rules)))
;; derp->yacc translation:
; wrapping makes $ and $$ available in the body:
(define (wrap-$ size body)
(define $$ (for/list ([i (in-range 1 (+ 1 size))]) `($ ,i)))
`(let-syntax
[($ (λ (stx)
(syntax-case stx ()
[(_ n) (datum->syntax
#'n
(string->symbol
(string-append
"$" (number->string
(syntax->datum #'n)))))])))]
(let-syntax
([$$ (λ (_) #'(list ,@$$))])
. ,body)))
(define (translate-terminal str)
(string->symbol str))
(define (translate-abstract-terminal sym)
(match sym
; Remove the extra layer of quoting used
; to denote classes of terminals from
; literal terminals, e.g. 'NUM versus :
[`(quote ,(and aterm (? symbol?)))
aterm]))
(define (translate-exp exp)
(match exp
[(? string?) (translate-terminal exp)]
[(? symbol?) exp]
[`(quote ,(? symbol?))
;=>
(translate-abstract-terminal exp)]))
(define (translate-reduction reduction)
(match reduction
[`($--> (seq . ,exps) . ,body)
(list (map translate-exp exps)
(wrap-$ (length exps) body))]))
(define (translate-rhs rhs)
(match rhs
[`(or . ,reductions)
(map translate-reduction reductions)]))
(define (translate-rule rule)
(match rule
[`(,nonterm ,rhs)
`(,nonterm ,@(translate-rhs rhs))]))
;; normalization ensures that all expressions on
;; right-hand sides are flattened.
(define (normalize-rule rule)
(match rule
[`(,nonterm ,exp)
;=>
`[,nonterm ,(normalize-rhs exp)]]))
(define (normalize-rhs exp)
(match (force-or exp)
[`(or . ,exps)
; =>
`(or ,@(map (compose flatten-$* force-$*) exps))]))
;; flattening converts an expression in the grammar into
;; something suitable for a yacc/BNF-style grammar.
;; For example, consider a derp-style rule like:
; term ::= (seq factor (rep (seq "+" term)))
; this needs to flatten to:
; term ::= (seq factor $rep1)
; $rep1 ::= (rep (seq "+" term))
; and then into:
; term ::= (seq factor $rep1)
; $rep1 ::= (rep $seq1)
; $seq1 ::= (seq "+" term)
; and then into:
; term ::= (seq factor $rep1)
; $rep1 ::= (seq $seq1 $rep1)
; | (seq)
; $seq1 ::= (seq "+" term)
; and, at this point, it is yacc/BNF-compatible.
; Technically, to keep the reductions the same,
; it becomes equivalent to:
; term ::= (seq factor $rep1)
; $rep1 ::= (cons $seq1 $rep1)
; | (seq)
; $seq1 ::= (seq "+" term)
(define (flatten-$* exp)
(match exp
[`($--> (seq . , exps) . ,body)
;=>
`($--> (seq ,@(map flatten-exp exps)) . ,body)]))
; flatten things that can't be a *sub*-expression:
; opt
; rep
; rep+
; seq
; $-->
(define (flatten-exp exp)
(match exp
[`(seq . ,_)
;=>
(define $nonterm (gensym '$nt))
(add-rule $nonterm (normalize-rhs exp))
$nonterm]
[`($--> . ,_)
;=>
(define $nonterm (gensym '$nt))
(add-rule $nonterm (normalize-rhs exp))
$nonterm]
[`(or . ,_)
;=>
(define $nonterm (gensym '$nt))
(add-rule $nonterm (normalize-rhs exp))
$nonterm]
[`(opt ,exp ,default-value)
;=>
(define $nonterm (gensym '$nt))
(add-rule $nonterm `(or ($--> (seq ,(flatten-exp exp)) ($ 1))
($--> (seq) ,default-value)))
$nonterm]
[`(opt ,exp)
;=>
(flatten-exp `(opt ,exp #f))]
[`(rep ,exp)
;=>
(define $nonterm (gensym '$nt))
(add-rule $nonterm `(or ($--> (seq ,(flatten-exp exp) ,$nonterm) (cons ($ 1) ($ 2)))
($--> (seq) '())))
$nonterm]
[`(rep+ ,exp)
;=>
(define $nonterm (gensym '$nt))
(define flattened-exp (flatten-exp exp))
(add-rule $nonterm `(or ($--> (seq ,flattened-exp ,$nonterm) (cons ($ 1) ($ 2)))
($--> (seq ,flattened-exp) (list ($ 1)))))
$nonterm]
[`(quote ,(and aterm (? symbol?)))
;=>
exp]
[(? symbol?)
;=>
exp]
[(? string?)
;=>
; Make literal terminals reduce to their own string value:
(define $nonterm (gensym (string->symbol (string-append "$" exp))))
(add-rule $nonterm `(or ($--> (seq ,exp) ,exp)))
$nonterm]))
(define old-rules (map normalize-rule rules))
(define new-rules (append old-rules extra-rules))
(map translate-rule new-rules)))
(require (for-syntax (submod "." impl)))
(define-syntax (derp2-parser stx)
(syntax-case stx (grammar)
[(_ clause ...)
(let ([clauses (syntax->list #'(clause ...))])
#`(cfg-parser
#,@(for/list ([clause clauses])
(syntax-case clause (grammar)
[(grammar rule ...)
#`(grammar #,@(datum->syntax clause
(compile-derp-rules
(desugar
(syntax->datum #'(rule ...))))))]
[other #'other]))))]))