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1 | ;;; Continuation-passing style (CPS) intermediate language (IL) |
2 | ||
3 | ;; Copyright (C) 2013 Free Software Foundation, Inc. | |
4 | ||
5 | ;;;; This library is free software; you can redistribute it and/or | |
6 | ;;;; modify it under the terms of the GNU Lesser General Public | |
7 | ;;;; License as published by the Free Software Foundation; either | |
8 | ;;;; version 3 of the License, or (at your option) any later version. | |
9 | ;;;; | |
10 | ;;;; This library is distributed in the hope that it will be useful, | |
11 | ;;;; but WITHOUT ANY WARRANTY; without even the implied warranty of | |
12 | ;;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
13 | ;;;; Lesser General Public License for more details. | |
14 | ;;;; | |
15 | ;;;; You should have received a copy of the GNU Lesser General Public | |
16 | ;;;; License along with this library; if not, write to the Free Software | |
17 | ;;;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA | |
18 | ||
19 | ;;; Commentary: | |
20 | ;;; | |
21 | ;;; This is the continuation-passing style (CPS) intermediate language | |
22 | ;;; (IL) for Guile. | |
23 | ;;; | |
24 | ;;; There are two kinds of terms in CPS: terms that bind continuations, | |
25 | ;;; and terms that call continuations. | |
26 | ;;; | |
27 | ;;; $letk binds a set of mutually recursive continuations, each one an | |
28 | ;;; instance of $cont. A $cont declares the name and source of a | |
29 | ;;; continuation, and then contains as a subterm the particular | |
30 | ;;; continuation instance: $kif for test continuations, $kargs for | |
31 | ;;; continuations that bind values, etc. | |
32 | ;;; | |
33 | ;;; $continue nodes call continuations. The expression contained in the | |
34 | ;;; $continue node determines the value or values that are passed to the | |
35 | ;;; target continuation: $const to pass a constant value, $values to | |
36 | ;;; pass multiple named values, etc. | |
37 | ;;; | |
38 | ;;; Additionally there is $letrec, a term that binds mutually recursive | |
39 | ;;; functions. The contification pass will turn $letrec into $letk if | |
40 | ;;; it can do so. Otherwise, the closure conversion pass will desugar | |
41 | ;;; $letrec into an equivalent sequence of make-closure primcalls and | |
42 | ;;; subsequent initializations of the captured variables of the | |
43 | ;;; closures. You can think of $letrec as pertaining to "high CPS", | |
44 | ;;; whereas later passes will only see "low CPS", which does not have | |
45 | ;;; $letrec. | |
46 | ;;; | |
47 | ;;; This particular formulation of CPS was inspired by Andrew Kennedy's | |
48 | ;;; 2007 paper, "Compiling with Continuations, Continued". All Guile | |
49 | ;;; hackers should read that excellent paper! As in Kennedy's paper, | |
50 | ;;; continuations are second-class, and may be thought of as basic block | |
51 | ;;; labels. All values are bound to variables using continuation calls: | |
52 | ;;; even constants! | |
53 | ;;; | |
54 | ;;; There are some Guile-specific quirks as well: | |
55 | ;;; | |
56 | ;;; - $ktrunc represents a continuation that receives multiple values, | |
57 | ;;; but which truncates them to some number of required values, | |
58 | ;;; possibly with a rest list. | |
59 | ;;; | |
60 | ;;; - $kentry labels an entry point for a $fun (a function), and | |
61 | ;;; contains a $ktail representing the formal argument which is the | |
62 | ;;; function's continuation. | |
63 | ;;; | |
64 | ;;; - $kentry also contains $kclause continuations, corresponding to | |
65 | ;;; the case-lambda clauses of the function. $kclause actually | |
66 | ;;; contains the clause body. This is because the $kclause | |
67 | ;;; logically matches or doesn't match a given set of actual | |
68 | ;;; arguments against a formal arity, then proceeds to a "body" | |
69 | ;;; continuation (which is a $kargs). | |
70 | ;;; | |
71 | ;;; That's to say that a $fun can be matched like this: | |
72 | ;;; | |
73 | ;;; (match f | |
74 | ;;; (($ $fun meta free | |
75 | ;;; ($ $cont kentry src | |
76 | ;;; ($ $kentry self ($ $cont ktail _ ($ $ktail)) | |
77 | ;;; (($ $kclause arity | |
78 | ;;; ($ $cont kbody _ ($ $kargs names syms body))) | |
79 | ;;; ...)))) | |
80 | ;;; #t)) | |
81 | ;;; | |
82 | ;;; A $continue to ktail is in tail position. $kentry, $kclause, | |
83 | ;;; and $ktail will never be seen elsewhere in a CPS term. | |
84 | ;;; | |
85 | ;;; - $prompt continues to the body of the prompt, having pushed on a | |
86 | ;;; prompt whose handler will continue at its "handler" | |
87 | ;;; continuation. The continuation of the prompt is responsible for | |
96af4a18 AW |
88 | ;;; popping the prompt. A $prompt also records the continuation |
89 | ;;; that pops the prompt, to make various static analyses easier. | |
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90 | ;;; |
91 | ;;; In summary: | |
92 | ;;; | |
93 | ;;; - $letk, $letrec, and $continue are terms. | |
94 | ;;; | |
95 | ;;; - $cont is a continuation, containing a continuation body ($kargs, | |
96 | ;;; $kif, etc). | |
97 | ;;; | |
98 | ;;; - $continue terms contain an expression ($call, $const, $fun, | |
99 | ;;; etc). | |
100 | ;;; | |
101 | ;;; See (language tree-il compile-cps) for details on how Tree-IL | |
102 | ;;; converts to CPS. | |
103 | ;;; | |
104 | ;;; Code: | |
105 | ||
106 | (define-module (language cps) | |
107 | #:use-module (ice-9 match) | |
108 | #:use-module ((srfi srfi-1) #:select (fold)) | |
109 | #:use-module (srfi srfi-9) | |
110 | #:use-module (srfi srfi-9 gnu) | |
111 | #:export (;; Helper. | |
112 | $arity | |
113 | make-$arity | |
114 | ||
115 | ;; Terms. | |
116 | $letk $continue $letrec | |
117 | ||
118 | ;; Continuations. | |
119 | $cont | |
120 | ||
121 | ;; Continuation bodies. | |
122 | $kif $ktrunc $kargs $kentry $ktail $kclause | |
123 | ||
124 | ;; Expressions. | |
125 | $var $void $const $prim $fun $call $primcall $values $prompt | |
126 | ||
127 | ;; Building macros. | |
128 | let-gensyms | |
129 | build-cps-term build-cps-cont build-cps-exp | |
130 | rewrite-cps-term rewrite-cps-cont rewrite-cps-exp | |
131 | ||
132 | ;; Misc. | |
133 | parse-cps unparse-cps | |
134 | fold-conts fold-local-conts)) | |
135 | ||
136 | ;; FIXME: Use SRFI-99, when Guile adds it. | |
137 | (define-syntax define-record-type* | |
138 | (lambda (x) | |
139 | (define (id-append ctx . syms) | |
140 | (datum->syntax ctx (apply symbol-append (map syntax->datum syms)))) | |
141 | (syntax-case x () | |
142 | ((_ name field ...) | |
143 | (and (identifier? #'name) (and-map identifier? #'(field ...))) | |
144 | (with-syntax ((cons (id-append #'name #'make- #'name)) | |
145 | (pred (id-append #'name #'name #'?)) | |
146 | ((getter ...) (map (lambda (f) | |
147 | (id-append f #'name #'- f)) | |
148 | #'(field ...)))) | |
149 | #'(define-record-type name | |
150 | (cons field ...) | |
151 | pred | |
152 | (field getter) | |
153 | ...)))))) | |
154 | ||
155 | (define-syntax-rule (define-cps-type name field ...) | |
156 | (begin | |
157 | (define-record-type* name field ...) | |
158 | (set-record-type-printer! name print-cps))) | |
159 | ||
160 | (define (print-cps exp port) | |
161 | (format port "#<cps ~S>" (unparse-cps exp))) | |
162 | ||
163 | ;; Helper. | |
164 | (define-record-type* $arity req opt rest kw allow-other-keys?) | |
165 | ||
166 | ;; Terms. | |
167 | (define-cps-type $letk conts body) | |
168 | (define-cps-type $continue k exp) | |
169 | (define-cps-type $letrec names syms funs body) | |
170 | ||
171 | ;; Continuations | |
172 | (define-cps-type $cont k src cont) | |
173 | (define-cps-type $kif kt kf) | |
174 | (define-cps-type $ktrunc arity k) | |
175 | (define-cps-type $kargs names syms body) | |
176 | (define-cps-type $kentry self tail clauses) | |
177 | (define-cps-type $ktail) | |
178 | (define-cps-type $kclause arity cont) | |
179 | ||
180 | ;; Expressions. | |
181 | (define-cps-type $var sym) | |
182 | (define-cps-type $void) | |
183 | (define-cps-type $const val) | |
184 | (define-cps-type $prim name) | |
185 | (define-cps-type $fun meta free body) | |
186 | (define-cps-type $call proc args) | |
187 | (define-cps-type $primcall name args) | |
188 | (define-cps-type $values args) | |
96af4a18 | 189 | (define-cps-type $prompt escape? tag handler pop) |
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190 | |
191 | (define-syntax let-gensyms | |
192 | (syntax-rules () | |
193 | ((_ (sym ...) body body* ...) | |
194 | (let ((sym (gensym (symbol->string 'sym))) ...) | |
195 | body body* ...)))) | |
196 | ||
197 | (define-syntax build-arity | |
198 | (syntax-rules (unquote) | |
199 | ((_ (unquote exp)) exp) | |
200 | ((_ (req opt rest kw allow-other-keys?)) | |
201 | (make-$arity req opt rest kw allow-other-keys?)))) | |
202 | ||
203 | (define-syntax build-cont-body | |
204 | (syntax-rules (unquote $kif $ktrunc $kargs $kentry $ktail $kclause) | |
205 | ((_ (unquote exp)) | |
206 | exp) | |
207 | ((_ ($kif kt kf)) | |
208 | (make-$kif kt kf)) | |
209 | ((_ ($ktrunc req rest kargs)) | |
210 | (make-$ktrunc (make-$arity req '() rest '() #f) kargs)) | |
211 | ((_ ($kargs (name ...) (sym ...) body)) | |
212 | (make-$kargs (list name ...) (list sym ...) (build-cps-term body))) | |
213 | ((_ ($kargs names syms body)) | |
214 | (make-$kargs names syms (build-cps-term body))) | |
215 | ((_ ($kentry self tail (unquote clauses))) | |
216 | (make-$kentry self (build-cps-cont tail) clauses)) | |
217 | ((_ ($kentry self tail (clause ...))) | |
218 | (make-$kentry self (build-cps-cont tail) (list (build-cps-cont clause) ...))) | |
219 | ((_ ($ktail)) | |
220 | (make-$ktail)) | |
221 | ((_ ($kclause arity cont)) | |
222 | (make-$kclause (build-arity arity) (build-cps-cont cont))))) | |
223 | ||
224 | (define-syntax build-cps-cont | |
225 | (syntax-rules (unquote) | |
226 | ((_ (unquote exp)) exp) | |
227 | ((_ (k src cont)) (make-$cont k src (build-cont-body cont))))) | |
228 | ||
229 | (define-syntax build-cps-exp | |
230 | (syntax-rules (unquote | |
231 | $var $void $const $prim $fun $call $primcall $values $prompt) | |
232 | ((_ (unquote exp)) exp) | |
233 | ((_ ($var sym)) (make-$var sym)) | |
234 | ((_ ($void)) (make-$void)) | |
235 | ((_ ($const val)) (make-$const val)) | |
236 | ((_ ($prim name)) (make-$prim name)) | |
237 | ((_ ($fun meta free body)) (make-$fun meta free (build-cps-cont body))) | |
238 | ((_ ($call proc (arg ...))) (make-$call proc (list arg ...))) | |
239 | ((_ ($call proc args)) (make-$call proc args)) | |
240 | ((_ ($primcall name (arg ...))) (make-$primcall name (list arg ...))) | |
241 | ((_ ($primcall name args)) (make-$primcall name args)) | |
242 | ((_ ($values (arg ...))) (make-$values (list arg ...))) | |
243 | ((_ ($values args)) (make-$values args)) | |
96af4a18 AW |
244 | ((_ ($prompt escape? tag handler pop)) |
245 | (make-$prompt escape? tag handler pop)))) | |
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246 | |
247 | (define-syntax build-cps-term | |
248 | (syntax-rules (unquote $letk $letk* $letconst $letrec $continue) | |
249 | ((_ (unquote exp)) | |
250 | exp) | |
251 | ((_ ($letk (unquote conts) body)) | |
252 | (make-$letk conts (build-cps-term body))) | |
253 | ((_ ($letk (cont ...) body)) | |
254 | (make-$letk (list (build-cps-cont cont) ...) | |
255 | (build-cps-term body))) | |
256 | ((_ ($letk* () body)) | |
257 | (build-cps-term body)) | |
258 | ((_ ($letk* (cont conts ...) body)) | |
259 | (build-cps-term ($letk (cont) ($letk* (conts ...) body)))) | |
260 | ((_ ($letconst () body)) | |
261 | (build-cps-term body)) | |
262 | ((_ ($letconst ((name sym val) tail ...) body)) | |
263 | (let-gensyms (kconst) | |
264 | (build-cps-term | |
265 | ($letk ((kconst #f ($kargs (name) (sym) ($letconst (tail ...) body)))) | |
266 | ($continue kconst ($const val)))))) | |
267 | ((_ ($letrec names gensyms funs body)) | |
268 | (make-$letrec names gensyms funs (build-cps-term body))) | |
269 | ((_ ($continue k exp)) | |
270 | (make-$continue k (build-cps-exp exp))))) | |
271 | ||
272 | (define-syntax-rule (rewrite-cps-term x (pat body) ...) | |
273 | (match x | |
274 | (pat (build-cps-term body)) ...)) | |
275 | (define-syntax-rule (rewrite-cps-cont x (pat body) ...) | |
276 | (match x | |
277 | (pat (build-cps-cont body)) ...)) | |
278 | (define-syntax-rule (rewrite-cps-exp x (pat body) ...) | |
279 | (match x | |
280 | (pat (build-cps-exp body)) ...)) | |
281 | ||
282 | (define (parse-cps exp) | |
283 | (define (src exp) | |
284 | (let ((props (source-properties exp))) | |
285 | (and (pair? props) props))) | |
286 | (match exp | |
287 | ;; Continuations. | |
288 | (('letconst k (name sym c) body) | |
289 | (build-cps-term | |
290 | ($letk ((k (src exp) ($kargs (name) (sym) | |
291 | ,(parse-cps body)))) | |
292 | ($continue k ($const c))))) | |
293 | (('let k (name sym val) body) | |
294 | (build-cps-term | |
295 | ($letk ((k (src exp) ($kargs (name) (sym) | |
296 | ,(parse-cps body)))) | |
297 | ,(parse-cps val)))) | |
298 | (('letk (cont ...) body) | |
299 | (build-cps-term | |
300 | ($letk ,(map parse-cps cont) ,(parse-cps body)))) | |
301 | (('k sym body) | |
302 | (build-cps-cont | |
303 | (sym (src exp) ,(parse-cps body)))) | |
304 | (('kif kt kf) | |
305 | (build-cont-body ($kif kt kf))) | |
306 | (('ktrunc req rest k) | |
307 | (build-cont-body ($ktrunc req rest k))) | |
308 | (('kargs names syms body) | |
309 | (build-cont-body ($kargs names syms ,(parse-cps body)))) | |
310 | (('kentry self tail clauses) | |
311 | (build-cont-body | |
312 | ($kentry self ,(parse-cps tail) ,(map parse-cps clauses)))) | |
313 | (('ktail) | |
314 | (build-cont-body | |
315 | ($ktail))) | |
316 | (('kclause (req opt rest kw allow-other-keys?) body) | |
317 | (build-cont-body | |
318 | ($kclause (req opt rest kw allow-other-keys?) | |
319 | ,(parse-cps body)))) | |
320 | (('kseq body) | |
321 | (build-cont-body ($kargs () () ,(parse-cps body)))) | |
322 | ||
323 | ;; Calls. | |
324 | (('continue k exp) | |
325 | (build-cps-term ($continue k ,(parse-cps exp)))) | |
326 | (('var sym) | |
327 | (build-cps-exp ($var sym))) | |
328 | (('void) | |
329 | (build-cps-exp ($void))) | |
330 | (('const exp) | |
331 | (build-cps-exp ($const exp))) | |
332 | (('prim name) | |
333 | (build-cps-exp ($prim name))) | |
334 | (('fun meta free body) | |
335 | (build-cps-exp ($fun meta free ,(parse-cps body)))) | |
336 | (('letrec ((name sym fun) ...) body) | |
337 | (build-cps-term | |
338 | ($letrec name sym (map parse-cps fun) ,(parse-cps body)))) | |
339 | (('call proc arg ...) | |
340 | (build-cps-exp ($call proc arg))) | |
341 | (('primcall name arg ...) | |
342 | (build-cps-exp ($primcall name arg))) | |
343 | (('values arg ...) | |
344 | (build-cps-exp ($values arg))) | |
96af4a18 AW |
345 | (('prompt escape? tag handler pop) |
346 | (build-cps-exp ($prompt escape? tag handler pop))) | |
80b01fd0 AW |
347 | (_ |
348 | (error "unexpected cps" exp)))) | |
349 | ||
350 | (define (unparse-cps exp) | |
351 | (match exp | |
352 | ;; Continuations. | |
353 | (($ $letk (($ $cont k src ($ $kargs (name) (sym) body))) | |
354 | ($ $continue k ($ $const c))) | |
355 | `(letconst ,k (,name ,sym ,c) | |
356 | ,(unparse-cps body))) | |
357 | (($ $letk (($ $cont k src ($ $kargs (name) (sym) body))) val) | |
358 | `(let ,k (,name ,sym ,(unparse-cps val)) | |
359 | ,(unparse-cps body))) | |
360 | (($ $letk conts body) | |
361 | `(letk ,(map unparse-cps conts) ,(unparse-cps body))) | |
362 | (($ $cont sym src body) | |
363 | `(k ,sym ,(unparse-cps body))) | |
364 | (($ $kif kt kf) | |
365 | `(kif ,kt ,kf)) | |
366 | (($ $ktrunc ($ $arity req () rest '() #f) k) | |
367 | `(ktrunc ,req ,rest ,k)) | |
368 | (($ $kargs () () body) | |
369 | `(kseq ,(unparse-cps body))) | |
370 | (($ $kargs names syms body) | |
371 | `(kargs ,names ,syms ,(unparse-cps body))) | |
372 | (($ $kentry self tail clauses) | |
373 | `(kentry ,self ,(unparse-cps tail) ,(map unparse-cps clauses))) | |
374 | (($ $ktail) | |
375 | `(ktail)) | |
376 | (($ $kclause ($ $arity req opt rest kw allow-other-keys?) body) | |
377 | `(kclause (,req ,opt ,rest ,kw ,allow-other-keys?) ,(unparse-cps body))) | |
378 | ||
379 | ;; Calls. | |
380 | (($ $continue k exp) | |
381 | `(continue ,k ,(unparse-cps exp))) | |
382 | (($ $var sym) | |
383 | `(var ,sym)) | |
384 | (($ $void) | |
385 | `(void)) | |
386 | (($ $const val) | |
387 | `(const ,val)) | |
388 | (($ $prim name) | |
389 | `(prim ,name)) | |
390 | (($ $fun meta free body) | |
391 | `(fun ,meta ,free ,(unparse-cps body))) | |
392 | (($ $letrec names syms funs body) | |
393 | `(letrec ,(map (lambda (name sym fun) | |
394 | (list name sym (unparse-cps fun))) | |
395 | names syms funs) | |
396 | ,(unparse-cps body))) | |
397 | (($ $call proc args) | |
398 | `(call ,proc ,@args)) | |
399 | (($ $primcall name args) | |
400 | `(primcall ,name ,@args)) | |
401 | (($ $values args) | |
402 | `(values ,@args)) | |
96af4a18 AW |
403 | (($ $prompt escape? tag handler pop) |
404 | `(prompt ,escape? ,tag ,handler ,pop)) | |
80b01fd0 AW |
405 | (_ |
406 | (error "unexpected cps" exp)))) | |
407 | ||
408 | (define (fold-conts proc seed fun) | |
409 | (define (cont-folder cont seed) | |
410 | (match cont | |
411 | (($ $cont k src cont) | |
412 | (let ((seed (proc k src cont seed))) | |
413 | (match cont | |
414 | (($ $kargs names syms body) | |
415 | (term-folder body seed)) | |
416 | ||
417 | (($ $kentry self tail clauses) | |
418 | (fold cont-folder (cont-folder tail seed) clauses)) | |
419 | ||
420 | (($ $kclause arity body) | |
421 | (cont-folder body seed)) | |
422 | ||
423 | (_ seed)))))) | |
424 | ||
425 | (define (fun-folder fun seed) | |
426 | (match fun | |
427 | (($ $fun meta free body) | |
428 | (cont-folder body seed)))) | |
429 | ||
430 | (define (term-folder term seed) | |
431 | (match term | |
432 | (($ $letk conts body) | |
433 | (fold cont-folder (term-folder body seed) conts)) | |
434 | ||
435 | (($ $continue k exp) | |
436 | (match exp | |
437 | (($ $fun) (fun-folder exp seed)) | |
438 | (_ seed))) | |
439 | ||
440 | (($ $letrec names syms funs body) | |
441 | (fold fun-folder (term-folder body seed) funs)))) | |
442 | ||
443 | (fun-folder fun seed)) | |
444 | ||
445 | (define (fold-local-conts proc seed cont) | |
446 | (define (cont-folder cont seed) | |
447 | (match cont | |
448 | (($ $cont k src cont) | |
449 | (let ((seed (proc k src cont seed))) | |
450 | (match cont | |
451 | (($ $kargs names syms body) | |
452 | (term-folder body seed)) | |
453 | ||
454 | (($ $kentry self tail clauses) | |
455 | (fold cont-folder (cont-folder tail seed) clauses)) | |
456 | ||
457 | (($ $kclause arity body) | |
458 | (cont-folder body seed)) | |
459 | ||
460 | (_ seed)))))) | |
461 | ||
462 | (define (term-folder term seed) | |
463 | (match term | |
464 | (($ $letk conts body) | |
465 | (fold cont-folder (term-folder body seed) conts)) | |
466 | ||
467 | (($ $continue) seed) | |
468 | ||
469 | (($ $letrec names syms funs body) (term-folder body seed)))) | |
470 | ||
471 | (cont-folder cont seed)) |