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1 | ;;; Continuation-passing style (CPS) intermediate language (IL) |
2 | ||
7ab76a83 | 3 | ;; Copyright (C) 2013, 2014 Free Software Foundation, Inc. |
80b01fd0 AW |
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 | |
6e422a35 AW |
28 | ;;; instance of $cont. A $cont declares the name of a continuation, and |
29 | ;;; then contains as a subterm the particular continuation instance: | |
30 | ;;; $kif for test continuations, $kargs for continuations that bind | |
31 | ;;; values, etc. | |
80b01fd0 AW |
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 | |
6e422a35 | 36 | ;;; pass multiple named values, etc. $continue nodes also record the source at which |
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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 | ;;; | |
36527695 | 56 | ;;; - $kreceive represents a continuation that receives multiple values, |
80b01fd0 AW |
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 $fun can be matched like this: | |
72 | ;;; | |
73 | ;;; (match f | |
6e422a35 AW |
74 | ;;; (($ $fun src meta free |
75 | ;;; ($ $cont kentry | |
80b01fd0 AW |
76 | ;;; ($ $kentry self ($ $cont ktail _ ($ $ktail)) |
77 | ;;; (($ $kclause arity | |
78 | ;;; ($ $cont kbody _ ($ $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 | |
7ab76a83 | 88 | ;;; popping the prompt. |
80b01fd0 AW |
89 | ;;; |
90 | ;;; In summary: | |
91 | ;;; | |
92 | ;;; - $letk, $letrec, and $continue are terms. | |
93 | ;;; | |
94 | ;;; - $cont is a continuation, containing a continuation body ($kargs, | |
95 | ;;; $kif, etc). | |
96 | ;;; | |
97 | ;;; - $continue terms contain an expression ($call, $const, $fun, | |
98 | ;;; etc). | |
99 | ;;; | |
100 | ;;; See (language tree-il compile-cps) for details on how Tree-IL | |
101 | ;;; converts to CPS. | |
102 | ;;; | |
103 | ;;; Code: | |
104 | ||
105 | (define-module (language cps) | |
106 | #:use-module (ice-9 match) | |
107 | #:use-module ((srfi srfi-1) #:select (fold)) | |
108 | #:use-module (srfi srfi-9) | |
109 | #:use-module (srfi srfi-9 gnu) | |
110 | #:export (;; Helper. | |
111 | $arity | |
112 | make-$arity | |
113 | ||
114 | ;; Terms. | |
115 | $letk $continue $letrec | |
116 | ||
117 | ;; Continuations. | |
118 | $cont | |
119 | ||
120 | ;; Continuation bodies. | |
36527695 | 121 | $kif $kreceive $kargs $kentry $ktail $kclause |
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122 | |
123 | ;; Expressions. | |
13085a82 | 124 | $void $const $prim $fun $call $primcall $values $prompt |
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125 | |
126 | ;; Building macros. | |
127 | let-gensyms | |
128 | build-cps-term build-cps-cont build-cps-exp | |
129 | rewrite-cps-term rewrite-cps-cont rewrite-cps-exp | |
130 | ||
131 | ;; Misc. | |
132 | parse-cps unparse-cps | |
133 | fold-conts fold-local-conts)) | |
134 | ||
135 | ;; FIXME: Use SRFI-99, when Guile adds it. | |
136 | (define-syntax define-record-type* | |
137 | (lambda (x) | |
138 | (define (id-append ctx . syms) | |
139 | (datum->syntax ctx (apply symbol-append (map syntax->datum syms)))) | |
140 | (syntax-case x () | |
141 | ((_ name field ...) | |
142 | (and (identifier? #'name) (and-map identifier? #'(field ...))) | |
143 | (with-syntax ((cons (id-append #'name #'make- #'name)) | |
144 | (pred (id-append #'name #'name #'?)) | |
145 | ((getter ...) (map (lambda (f) | |
146 | (id-append f #'name #'- f)) | |
147 | #'(field ...)))) | |
148 | #'(define-record-type name | |
149 | (cons field ...) | |
150 | pred | |
151 | (field getter) | |
152 | ...)))))) | |
153 | ||
154 | (define-syntax-rule (define-cps-type name field ...) | |
155 | (begin | |
156 | (define-record-type* name field ...) | |
157 | (set-record-type-printer! name print-cps))) | |
158 | ||
159 | (define (print-cps exp port) | |
160 | (format port "#<cps ~S>" (unparse-cps exp))) | |
161 | ||
162 | ;; Helper. | |
163 | (define-record-type* $arity req opt rest kw allow-other-keys?) | |
164 | ||
165 | ;; Terms. | |
166 | (define-cps-type $letk conts body) | |
6e422a35 | 167 | (define-cps-type $continue k src exp) |
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168 | (define-cps-type $letrec names syms funs body) |
169 | ||
170 | ;; Continuations | |
6e422a35 | 171 | (define-cps-type $cont k cont) |
80b01fd0 | 172 | (define-cps-type $kif kt kf) |
36527695 | 173 | (define-cps-type $kreceive arity k) |
80b01fd0 AW |
174 | (define-cps-type $kargs names syms body) |
175 | (define-cps-type $kentry self tail clauses) | |
176 | (define-cps-type $ktail) | |
177 | (define-cps-type $kclause arity cont) | |
178 | ||
179 | ;; Expressions. | |
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180 | (define-cps-type $void) |
181 | (define-cps-type $const val) | |
182 | (define-cps-type $prim name) | |
6e422a35 | 183 | (define-cps-type $fun src meta free body) |
80b01fd0 AW |
184 | (define-cps-type $call proc args) |
185 | (define-cps-type $primcall name args) | |
186 | (define-cps-type $values args) | |
7ab76a83 | 187 | (define-cps-type $prompt escape? tag handler) |
80b01fd0 AW |
188 | |
189 | (define-syntax let-gensyms | |
190 | (syntax-rules () | |
191 | ((_ (sym ...) body body* ...) | |
192 | (let ((sym (gensym (symbol->string 'sym))) ...) | |
193 | body body* ...)))) | |
194 | ||
195 | (define-syntax build-arity | |
196 | (syntax-rules (unquote) | |
197 | ((_ (unquote exp)) exp) | |
198 | ((_ (req opt rest kw allow-other-keys?)) | |
199 | (make-$arity req opt rest kw allow-other-keys?)))) | |
200 | ||
201 | (define-syntax build-cont-body | |
36527695 | 202 | (syntax-rules (unquote $kif $kreceive $kargs $kentry $ktail $kclause) |
80b01fd0 AW |
203 | ((_ (unquote exp)) |
204 | exp) | |
205 | ((_ ($kif kt kf)) | |
206 | (make-$kif kt kf)) | |
36527695 AW |
207 | ((_ ($kreceive req rest kargs)) |
208 | (make-$kreceive (make-$arity req '() rest '() #f) kargs)) | |
80b01fd0 AW |
209 | ((_ ($kargs (name ...) (sym ...) body)) |
210 | (make-$kargs (list name ...) (list sym ...) (build-cps-term body))) | |
211 | ((_ ($kargs names syms body)) | |
212 | (make-$kargs names syms (build-cps-term body))) | |
213 | ((_ ($kentry self tail (unquote clauses))) | |
214 | (make-$kentry self (build-cps-cont tail) clauses)) | |
215 | ((_ ($kentry self tail (clause ...))) | |
216 | (make-$kentry self (build-cps-cont tail) (list (build-cps-cont clause) ...))) | |
217 | ((_ ($ktail)) | |
218 | (make-$ktail)) | |
219 | ((_ ($kclause arity cont)) | |
220 | (make-$kclause (build-arity arity) (build-cps-cont cont))))) | |
221 | ||
222 | (define-syntax build-cps-cont | |
223 | (syntax-rules (unquote) | |
224 | ((_ (unquote exp)) exp) | |
6e422a35 | 225 | ((_ (k cont)) (make-$cont k (build-cont-body cont))))) |
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226 | |
227 | (define-syntax build-cps-exp | |
228 | (syntax-rules (unquote | |
13085a82 | 229 | $void $const $prim $fun $call $primcall $values $prompt) |
80b01fd0 | 230 | ((_ (unquote exp)) exp) |
80b01fd0 AW |
231 | ((_ ($void)) (make-$void)) |
232 | ((_ ($const val)) (make-$const val)) | |
233 | ((_ ($prim name)) (make-$prim name)) | |
6e422a35 AW |
234 | ((_ ($fun src meta free body)) |
235 | (make-$fun src meta free (build-cps-cont body))) | |
80b01fd0 AW |
236 | ((_ ($call proc (arg ...))) (make-$call proc (list arg ...))) |
237 | ((_ ($call proc args)) (make-$call proc args)) | |
238 | ((_ ($primcall name (arg ...))) (make-$primcall name (list arg ...))) | |
239 | ((_ ($primcall name args)) (make-$primcall name args)) | |
240 | ((_ ($values (arg ...))) (make-$values (list arg ...))) | |
241 | ((_ ($values args)) (make-$values args)) | |
7ab76a83 AW |
242 | ((_ ($prompt escape? tag handler)) |
243 | (make-$prompt escape? tag handler)))) | |
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244 | |
245 | (define-syntax build-cps-term | |
246 | (syntax-rules (unquote $letk $letk* $letconst $letrec $continue) | |
247 | ((_ (unquote exp)) | |
248 | exp) | |
249 | ((_ ($letk (unquote conts) body)) | |
250 | (make-$letk conts (build-cps-term body))) | |
251 | ((_ ($letk (cont ...) body)) | |
252 | (make-$letk (list (build-cps-cont cont) ...) | |
253 | (build-cps-term body))) | |
254 | ((_ ($letk* () body)) | |
255 | (build-cps-term body)) | |
256 | ((_ ($letk* (cont conts ...) body)) | |
257 | (build-cps-term ($letk (cont) ($letk* (conts ...) body)))) | |
258 | ((_ ($letconst () body)) | |
259 | (build-cps-term body)) | |
260 | ((_ ($letconst ((name sym val) tail ...) body)) | |
261 | (let-gensyms (kconst) | |
262 | (build-cps-term | |
6e422a35 AW |
263 | ($letk ((kconst ($kargs (name) (sym) ($letconst (tail ...) body)))) |
264 | ($continue kconst (let ((props (source-properties val))) | |
265 | (and (pair? props) props)) | |
266 | ($const val)))))) | |
80b01fd0 AW |
267 | ((_ ($letrec names gensyms funs body)) |
268 | (make-$letrec names gensyms funs (build-cps-term body))) | |
6e422a35 AW |
269 | ((_ ($continue k src exp)) |
270 | (make-$continue k src (build-cps-exp exp))))) | |
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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 | |
6e422a35 AW |
290 | ($letk ((k ($kargs (name) (sym) |
291 | ,(parse-cps body)))) | |
292 | ($continue k (src exp) ($const c))))) | |
80b01fd0 AW |
293 | (('let k (name sym val) body) |
294 | (build-cps-term | |
6e422a35 AW |
295 | ($letk ((k ($kargs (name) (sym) |
296 | ,(parse-cps body)))) | |
80b01fd0 AW |
297 | ,(parse-cps val)))) |
298 | (('letk (cont ...) body) | |
299 | (build-cps-term | |
300 | ($letk ,(map parse-cps cont) ,(parse-cps body)))) | |
301 | (('k sym body) | |
302 | (build-cps-cont | |
6e422a35 | 303 | (sym ,(parse-cps body)))) |
80b01fd0 AW |
304 | (('kif kt kf) |
305 | (build-cont-body ($kif kt kf))) | |
36527695 AW |
306 | (('kreceive req rest k) |
307 | (build-cont-body ($kreceive req rest k))) | |
80b01fd0 AW |
308 | (('kargs names syms body) |
309 | (build-cont-body ($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) | |
6e422a35 | 325 | (build-cps-term ($continue k (src exp) ,(parse-cps exp)))) |
80b01fd0 AW |
326 | (('void) |
327 | (build-cps-exp ($void))) | |
328 | (('const exp) | |
329 | (build-cps-exp ($const exp))) | |
330 | (('prim name) | |
331 | (build-cps-exp ($prim name))) | |
332 | (('fun meta free body) | |
6e422a35 | 333 | (build-cps-exp ($fun (src exp) meta free ,(parse-cps body)))) |
80b01fd0 AW |
334 | (('letrec ((name sym fun) ...) body) |
335 | (build-cps-term | |
336 | ($letrec name sym (map parse-cps fun) ,(parse-cps body)))) | |
337 | (('call proc arg ...) | |
338 | (build-cps-exp ($call proc arg))) | |
339 | (('primcall name arg ...) | |
340 | (build-cps-exp ($primcall name arg))) | |
341 | (('values arg ...) | |
342 | (build-cps-exp ($values arg))) | |
7ab76a83 AW |
343 | (('prompt escape? tag handler) |
344 | (build-cps-exp ($prompt escape? tag handler))) | |
80b01fd0 AW |
345 | (_ |
346 | (error "unexpected cps" exp)))) | |
347 | ||
348 | (define (unparse-cps exp) | |
349 | (match exp | |
350 | ;; Continuations. | |
6e422a35 AW |
351 | (($ $letk (($ $cont k ($ $kargs (name) (sym) body))) |
352 | ($ $continue k src ($ $const c))) | |
80b01fd0 AW |
353 | `(letconst ,k (,name ,sym ,c) |
354 | ,(unparse-cps body))) | |
6e422a35 | 355 | (($ $letk (($ $cont k ($ $kargs (name) (sym) body))) val) |
80b01fd0 AW |
356 | `(let ,k (,name ,sym ,(unparse-cps val)) |
357 | ,(unparse-cps body))) | |
358 | (($ $letk conts body) | |
359 | `(letk ,(map unparse-cps conts) ,(unparse-cps body))) | |
6e422a35 | 360 | (($ $cont sym body) |
80b01fd0 AW |
361 | `(k ,sym ,(unparse-cps body))) |
362 | (($ $kif kt kf) | |
363 | `(kif ,kt ,kf)) | |
36527695 AW |
364 | (($ $kreceive ($ $arity req () rest '() #f) k) |
365 | `(kreceive ,req ,rest ,k)) | |
80b01fd0 AW |
366 | (($ $kargs () () body) |
367 | `(kseq ,(unparse-cps body))) | |
368 | (($ $kargs names syms body) | |
369 | `(kargs ,names ,syms ,(unparse-cps body))) | |
370 | (($ $kentry self tail clauses) | |
371 | `(kentry ,self ,(unparse-cps tail) ,(map unparse-cps clauses))) | |
372 | (($ $ktail) | |
373 | `(ktail)) | |
374 | (($ $kclause ($ $arity req opt rest kw allow-other-keys?) body) | |
375 | `(kclause (,req ,opt ,rest ,kw ,allow-other-keys?) ,(unparse-cps body))) | |
376 | ||
377 | ;; Calls. | |
6e422a35 | 378 | (($ $continue k src exp) |
80b01fd0 | 379 | `(continue ,k ,(unparse-cps exp))) |
80b01fd0 AW |
380 | (($ $void) |
381 | `(void)) | |
382 | (($ $const val) | |
383 | `(const ,val)) | |
384 | (($ $prim name) | |
385 | `(prim ,name)) | |
6e422a35 | 386 | (($ $fun src meta free body) |
80b01fd0 AW |
387 | `(fun ,meta ,free ,(unparse-cps body))) |
388 | (($ $letrec names syms funs body) | |
389 | `(letrec ,(map (lambda (name sym fun) | |
390 | (list name sym (unparse-cps fun))) | |
391 | names syms funs) | |
392 | ,(unparse-cps body))) | |
393 | (($ $call proc args) | |
394 | `(call ,proc ,@args)) | |
395 | (($ $primcall name args) | |
396 | `(primcall ,name ,@args)) | |
397 | (($ $values args) | |
398 | `(values ,@args)) | |
7ab76a83 AW |
399 | (($ $prompt escape? tag handler) |
400 | `(prompt ,escape? ,tag ,handler)) | |
80b01fd0 AW |
401 | (_ |
402 | (error "unexpected cps" exp)))) | |
403 | ||
404 | (define (fold-conts proc seed fun) | |
405 | (define (cont-folder cont seed) | |
406 | (match cont | |
6e422a35 AW |
407 | (($ $cont k cont) |
408 | (let ((seed (proc k cont seed))) | |
80b01fd0 AW |
409 | (match cont |
410 | (($ $kargs names syms body) | |
411 | (term-folder body seed)) | |
412 | ||
413 | (($ $kentry self tail clauses) | |
414 | (fold cont-folder (cont-folder tail seed) clauses)) | |
415 | ||
416 | (($ $kclause arity body) | |
417 | (cont-folder body seed)) | |
418 | ||
419 | (_ seed)))))) | |
420 | ||
421 | (define (fun-folder fun seed) | |
422 | (match fun | |
6e422a35 | 423 | (($ $fun src meta free body) |
80b01fd0 AW |
424 | (cont-folder body seed)))) |
425 | ||
426 | (define (term-folder term seed) | |
427 | (match term | |
428 | (($ $letk conts body) | |
429 | (fold cont-folder (term-folder body seed) conts)) | |
430 | ||
6e422a35 | 431 | (($ $continue k src exp) |
80b01fd0 AW |
432 | (match exp |
433 | (($ $fun) (fun-folder exp seed)) | |
434 | (_ seed))) | |
435 | ||
436 | (($ $letrec names syms funs body) | |
437 | (fold fun-folder (term-folder body seed) funs)))) | |
438 | ||
439 | (fun-folder fun seed)) | |
440 | ||
441 | (define (fold-local-conts proc seed cont) | |
442 | (define (cont-folder cont seed) | |
443 | (match cont | |
6e422a35 AW |
444 | (($ $cont k cont) |
445 | (let ((seed (proc k cont seed))) | |
80b01fd0 AW |
446 | (match cont |
447 | (($ $kargs names syms body) | |
448 | (term-folder body seed)) | |
449 | ||
450 | (($ $kentry self tail clauses) | |
451 | (fold cont-folder (cont-folder tail seed) clauses)) | |
452 | ||
453 | (($ $kclause arity body) | |
454 | (cont-folder body seed)) | |
455 | ||
456 | (_ seed)))))) | |
457 | ||
458 | (define (term-folder term seed) | |
459 | (match term | |
460 | (($ $letk conts body) | |
461 | (fold cont-folder (term-folder body seed) conts)) | |
462 | ||
463 | (($ $continue) seed) | |
464 | ||
465 | (($ $letrec names syms funs body) (term-folder body seed)))) | |
466 | ||
467 | (cont-folder cont seed)) |