Merge remote-tracking branch 'origin/stable-2.0'
[bpt/guile.git] / module / ice-9 / eval.scm
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1;;; -*- mode: scheme; coding: utf-8; -*-
2
6fc3eae4 3;;;; Copyright (C) 2009, 2010, 2011
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4;;;; Free Software Foundation, Inc.
5;;;;
6;;;; This library is free software; you can redistribute it and/or
7;;;; modify it under the terms of the GNU Lesser General Public
8;;;; License as published by the Free Software Foundation; either
9;;;; version 3 of the License, or (at your option) any later version.
10;;;;
11;;;; This library is distributed in the hope that it will be useful,
12;;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
13;;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14;;;; Lesser General Public License for more details.
15;;;;
16;;;; You should have received a copy of the GNU Lesser General Public
17;;;; License along with this library; if not, write to the Free Software
18;;;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
19;;;;
20
21\f
22
23;;; Commentary:
24
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25;;; Scheme eval, written in Scheme.
26;;;
27;;; Expressions are first expanded, by the syntax expander (i.e.
28;;; psyntax), then memoized into internal forms. The evaluator itself
29;;; only operates on the internal forms ("memoized expressions").
30;;;
31;;; Environments are represented as linked lists of the form (VAL ... .
32;;; MOD). If MOD is #f, it means the environment was captured before
33;;; modules were booted. If MOD is the literal value '(), we are
34;;; evaluating at the top level, and so should track changes to the
35;;; current module.
36;;;
37;;; Evaluate this in Emacs to make code indentation work right:
38;;;
39;;; (put 'memoized-expression-case 'scheme-indent-function 1)
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40;;;
41
42;;; Code:
43
44\f
45
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46(eval-when (compile)
47 (define-syntax capture-env
48 (syntax-rules ()
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49 ((_ (exp ...))
50 (let ((env (exp ...)))
51 (capture-env env)))
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52 ((_ env)
53 (if (null? env)
54 (current-module)
55 (if (not env)
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56 ;; the and current-module checks that modules are booted,
57 ;; and thus the-root-module is defined
5f161164 58 (and (current-module) the-root-module)
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59 env)))))
60
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61 ;; Fast case for procedures with fixed arities.
62 (define-syntax make-fixed-closure
4abb824c 63 (lambda (x)
9331f91c 64 (define *max-static-argument-count* 8)
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65 (define (make-formals n)
66 (map (lambda (i)
67 (datum->syntax
68 x
69 (string->symbol
70 (string (integer->char (+ (char->integer #\a) i))))))
71 (iota n)))
72 (syntax-case x ()
d8a071fc 73 ((_ eval nreq body env) (not (identifier? #'env))
4abb824c 74 #'(let ((e env))
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75 (make-fixed-closure eval nreq body e)))
76 ((_ eval nreq body env)
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77 #`(case nreq
78 #,@(map (lambda (nreq)
79 (let ((formals (make-formals nreq)))
80 #`((#,nreq)
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81 (lambda (#,@formals)
82 (eval body
83 (cons* #,@(reverse formals) env))))))
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84 (iota *max-static-argument-count*))
85 (else
86 #,(let ((formals (make-formals *max-static-argument-count*)))
87 #`(lambda (#,@formals . more)
88 (let lp ((new-env (cons* #,@(reverse formals) env))
89 (nreq (- nreq #,*max-static-argument-count*))
90 (args more))
91 (if (zero? nreq)
92 (eval body
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93 (if (null? args)
94 new-env
95 (scm-error 'wrong-number-of-args
96 "eval" "Wrong number of arguments"
97 '() #f)))
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98 (if (null? args)
99 (scm-error 'wrong-number-of-args
100 "eval" "Wrong number of arguments"
101 '() #f)
102 (lp (cons (car args) new-env)
103 (1- nreq)
104 (cdr args)))))))))))))
105
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106 (define-syntax call
107 (lambda (x)
108 (define *max-static-call-count* 4)
109 (syntax-case x ()
110 ((_ eval proc nargs args env) (identifier? #'env)
111 #`(case nargs
112 #,@(map (lambda (nargs)
113 #`((#,nargs)
114 (proc
115 #,@(map
116 (lambda (n)
117 (let lp ((n n) (args #'args))
118 (if (zero? n)
119 #`(eval (car #,args) env)
120 (lp (1- n) #`(cdr #,args)))))
121 (iota nargs)))))
122 (iota *max-static-call-count*))
123 (else
124 (apply proc
125 #,@(map
126 (lambda (n)
127 (let lp ((n n) (args #'args))
128 (if (zero? n)
129 #`(eval (car #,args) env)
130 (lp (1- n) #`(cdr #,args)))))
131 (iota *max-static-call-count*))
132 (let lp ((exps #,(let lp ((n *max-static-call-count*)
133 (args #'args))
134 (if (zero? n)
135 args
136 (lp (1- n) #`(cdr #,args)))))
137 (args '()))
138 (if (null? exps)
139 (reverse args)
140 (lp (cdr exps)
141 (cons (eval (car exps) env) args)))))))))))
142
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143 ;; This macro could be more straightforward if the compiler had better
144 ;; copy propagation. As it is we do some copy propagation by hand.
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145 (define-syntax mx-bind
146 (lambda (x)
147 (syntax-case x ()
148 ((_ data () body)
149 #'body)
150 ((_ data (a . b) body) (and (identifier? #'a) (identifier? #'b))
151 #'(let ((a (car data))
152 (b (cdr data)))
153 body))
154 ((_ data (a . b) body) (identifier? #'a)
155 #'(let ((a (car data))
156 (xb (cdr data)))
157 (mx-bind xb b body)))
158 ((_ data (a . b) body)
159 #'(let ((xa (car data))
160 (xb (cdr data)))
161 (mx-bind xa a (mx-bind xb b body))))
162 ((_ data v body) (identifier? #'v)
163 #'(let ((v data))
164 body)))))
165
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166 ;; The resulting nested if statements will be an O(n) dispatch. Once
167 ;; we compile `case' effectively, this situation will improve.
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168 (define-syntax mx-match
169 (lambda (x)
170 (syntax-case x (quote)
171 ((_ mx data tag)
172 #'(error "what" mx))
173 ((_ mx data tag (('type pat) body) c* ...)
174 #`(if (eqv? tag #,(or (memoized-typecode (syntax->datum #'type))
175 (error "not a typecode" #'type)))
176 (mx-bind data pat body)
177 (mx-match mx data tag c* ...))))))
178
179 (define-syntax memoized-expression-case
180 (lambda (x)
181 (syntax-case x ()
182 ((_ mx c ...)
183 #'(let ((tag (memoized-expression-typecode mx))
184 (data (memoized-expression-data mx)))
185 (mx-match mx data tag c ...)))))))
186
187
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188;;;
189;;; On 18 Feb 2010, I did a profile of how often the various memoized expression
190;;; types occur when getting to a prompt on a fresh build. Here are the numbers
191;;; I got:
192;;;
193;;; lexical-ref: 32933054
194;;; call: 20281547
195;;; toplevel-ref: 13228724
196;;; if: 9156156
197;;; quote: 6610137
198;;; let: 2619707
199;;; lambda: 1010921
200;;; begin: 948945
201;;; lexical-set: 509862
202;;; call-with-values: 139668
203;;; apply: 49402
204;;; module-ref: 14468
205;;; define: 1259
206;;; toplevel-set: 328
207;;; dynwind: 162
208;;; with-fluids: 0
209;;; call/cc: 0
210;;; module-set: 0
211;;;
212;;; So until we compile `case' into a computed goto, we'll order the clauses in
213;;; `eval' in this order, to put the most frequent cases first.
214;;;
215
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216(define primitive-eval
217 (let ()
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218 ;; We pre-generate procedures with fixed arities, up to some number of
219 ;; arguments; see make-fixed-closure above.
220
221 ;; A unique marker for unbound keywords.
222 (define unbound-arg (list 'unbound-arg))
223
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224 ;; Procedures with rest, optional, or keyword arguments, potentially with
225 ;; multiple arities, as with case-lambda.
d8a071fc 226 (define (make-general-closure env body nreq rest? nopt kw inits alt)
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227 (define alt-proc
228 (and alt
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229 (let* ((body (car alt))
230 (nreq (cadr alt))
231 (rest (if (null? (cddr alt)) #f (caddr alt)))
232 (tail (and (pair? (cddr alt)) (pair? (cdddr alt)) (cdddr alt)))
233 (nopt (if tail (car tail) 0))
234 (kw (and tail (cadr tail)))
235 (inits (if tail (caddr tail) '()))
236 (alt (and tail (cadddr tail))))
237 (make-general-closure env body nreq rest nopt kw inits alt))))
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238 (define (set-procedure-arity! proc)
239 (let lp ((alt alt) (nreq nreq) (nopt nopt) (rest? rest?))
240 (if (not alt)
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241 (begin
242 (set-procedure-property! proc 'arglist
243 (list nreq
244 nopt
245 (if kw (cdr kw) '())
246 (and kw (car kw))
247 (and rest? '_)))
248 (set-procedure-minimum-arity! proc nreq nopt rest?))
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249 (let* ((nreq* (cadr alt))
250 (rest?* (if (null? (cddr alt)) #f (caddr alt)))
251 (tail (and (pair? (cddr alt)) (pair? (cdddr alt)) (cdddr alt)))
252 (nopt* (if tail (car tail) 0))
253 (alt* (and tail (cadddr tail))))
254 (if (or (< nreq* nreq)
255 (and (= nreq* nreq)
256 (if rest?
257 (and rest?* (> nopt* nopt))
258 (or rest?* (> nopt* nopt)))))
259 (lp alt* nreq* nopt* rest?*)
260 (lp alt* nreq nopt rest?)))))
261 proc)
262 (set-procedure-arity!
263 (lambda %args
264 (let lp ((env env)
265 (nreq* nreq)
266 (args %args))
267 (if (> nreq* 0)
268 ;; First, bind required arguments.
269 (if (null? args)
270 (if alt
271 (apply alt-proc %args)
272 (scm-error 'wrong-number-of-args
273 "eval" "Wrong number of arguments"
274 '() #f))
275 (lp (cons (car args) env)
276 (1- nreq*)
277 (cdr args)))
278 ;; Move on to optional arguments.
279 (if (not kw)
280 ;; Without keywords, bind optionals from arguments.
281 (let lp ((env env)
282 (nopt nopt)
283 (args args)
284 (inits inits))
285 (if (zero? nopt)
286 (if rest?
287 (eval body (cons args env))
288 (if (null? args)
289 (eval body env)
290 (if alt
291 (apply alt-proc %args)
292 (scm-error 'wrong-number-of-args
293 "eval" "Wrong number of arguments"
294 '() #f))))
295 (if (null? args)
296 (lp (cons (eval (car inits) env) env)
297 (1- nopt) args (cdr inits))
298 (lp (cons (car args) env)
299 (1- nopt) (cdr args) (cdr inits)))))
300 ;; With keywords, we stop binding optionals at the first
301 ;; keyword.
302 (let lp ((env env)
303 (nopt* nopt)
304 (args args)
305 (inits inits))
306 (if (> nopt* 0)
307 (if (or (null? args) (keyword? (car args)))
308 (lp (cons (eval (car inits) env) env)
309 (1- nopt*) args (cdr inits))
310 (lp (cons (car args) env)
311 (1- nopt*) (cdr args) (cdr inits)))
312 ;; Finished with optionals.
313 (let* ((aok (car kw))
314 (kw (cdr kw))
315 (kw-base (+ nopt nreq (if rest? 1 0)))
316 (imax (let lp ((imax (1- kw-base)) (kw kw))
317 (if (null? kw)
318 imax
319 (lp (max (cdar kw) imax)
320 (cdr kw)))))
321 ;; Fill in kwargs with "undefined" vals.
322 (env (let lp ((i kw-base)
323 ;; Also, here we bind the rest
324 ;; arg, if any.
325 (env (if rest? (cons args env) env)))
326 (if (<= i imax)
327 (lp (1+ i) (cons unbound-arg env))
328 env))))
329 ;; Now scan args for keywords.
330 (let lp ((args args))
331 (if (and (pair? args) (pair? (cdr args))
332 (keyword? (car args)))
333 (let ((kw-pair (assq (car args) kw))
334 (v (cadr args)))
335 (if kw-pair
336 ;; Found a known keyword; set its value.
337 (list-set! env (- imax (cdr kw-pair)) v)
338 ;; Unknown keyword.
339 (if (not aok)
340 (scm-error 'keyword-argument-error
341 "eval" "Unrecognized keyword"
342 '() #f)))
343 (lp (cddr args)))
344 (if (pair? args)
345 (if rest?
346 ;; Be lenient parsing rest args.
347 (lp (cdr args))
348 (scm-error 'keyword-argument-error
349 "eval" "Invalid keyword"
350 '() #f))
351 ;; Finished parsing keywords. Fill in
352 ;; uninitialized kwargs by evalling init
353 ;; expressions in their appropriate
354 ;; environment.
355 (let lp ((i (- imax kw-base))
356 (inits inits))
357 (if (pair? inits)
358 (let ((tail (list-tail env i)))
359 (if (eq? (car tail) unbound-arg)
360 (set-car! tail
361 (eval (car inits)
362 (cdr tail))))
363 (lp (1- i) (cdr inits)))
364 ;; Finally, eval the body.
365 (eval body env)))))))))))))))
d8a071fc 366
b2b554ef 367 ;; The "engine". EXP is a memoized expression.
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368 (define (eval exp env)
369 (memoized-expression-case exp
21ec0bd9 370 (('lexical-ref n)
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371 (list-ref env n))
372
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373 (('call (f nargs . args))
374 (let ((proc (eval f env)))
375 (call eval proc nargs args env)))
376
377 (('toplevel-ref var-or-sym)
378 (variable-ref
379 (if (variable? var-or-sym)
380 var-or-sym
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381 (memoize-variable-access! exp
382 (capture-env (if (pair? env)
383 (cdr (last-pair env))
384 env))))))
21ec0bd9 385
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386 (('if (test consequent . alternate))
387 (if (eval test env)
388 (eval consequent env)
389 (eval alternate env)))
390
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391 (('quote x)
392 x)
393
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394 (('let (inits . body))
395 (let lp ((inits inits) (new-env (capture-env env)))
396 (if (null? inits)
397 (eval body new-env)
398 (lp (cdr inits)
399 (cons (eval (car inits) env) new-env)))))
400
8f9c5b58 401 (('lambda (body nreq . tail))
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402 (if (null? tail)
403 (make-fixed-closure eval nreq body (capture-env env))
404 (if (null? (cdr tail))
405 (make-general-closure (capture-env env) body nreq (car tail)
406 0 #f '() #f)
407 (apply make-general-closure (capture-env env) body nreq tail))))
408
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409 (('seq (head . tail))
410 (begin
411 (eval head env)
412 (eval tail env)))
413
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414 (('lexical-set! (n . x))
415 (let ((val (eval x env)))
bb0c8157 416 (list-set! env n val)))
5161a3c0 417
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418 (('call-with-values (producer . consumer))
419 (call-with-values (eval producer env)
420 (eval consumer env)))
421
422 (('apply (f args))
423 (apply (eval f env) (eval args env)))
424
425 (('module-ref var-or-spec)
5161a3c0 426 (variable-ref
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427 (if (variable? var-or-spec)
428 var-or-spec
429 (memoize-variable-access! exp #f))))
5161a3c0 430
21ec0bd9 431 (('define (name . x))
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432 (let ((x (eval x env)))
433 (if (and (procedure? x) (not (procedure-property x 'name)))
434 (set-procedure-property! x 'name name))
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435 (define! name x)
436 (if #f #f)))
21ec0bd9 437
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438 (('toplevel-set! (var-or-sym . x))
439 (variable-set!
440 (if (variable? var-or-sym)
441 var-or-sym
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442 (memoize-variable-access! exp
443 (capture-env (if (pair? env)
444 (cdr (last-pair env))
445 env))))
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446 (eval x env)))
447
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448 (('dynwind (in exp . out))
449 (dynamic-wind (eval in env)
450 (lambda () (eval exp env))
451 (eval out env)))
452
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453 (('with-fluids (fluids vals . exp))
454 (let* ((fluids (map (lambda (x) (eval x env)) fluids))
455 (vals (map (lambda (x) (eval x env)) vals)))
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456 (let lp ((fluids fluids) (vals vals))
457 (if (null? fluids)
458 (eval exp env)
459 (with-fluids (((car fluids) (car vals)))
460 (lp (cdr fluids) (cdr vals)))))))
bb0229b5 461
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462 (('prompt (tag exp . handler))
463 (@prompt (eval tag env)
464 (eval exp env)
465 (eval handler env)))
466
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467 (('call/cc proc)
468 (call/cc (eval proc env)))
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469
470 (('module-set! (x . var-or-spec))
471 (variable-set!
472 (if (variable? var-or-spec)
473 var-or-spec
474 (memoize-variable-access! exp #f))
475 (eval x env)))))
476
b2b554ef 477 ;; primitive-eval
5161a3c0 478 (lambda (exp)
b2b554ef 479 "Evaluate @var{exp} in the current module."
5161a3c0 480 (eval
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481 (memoize-expression
482 (if (macroexpanded? exp)
483 exp
484 ((module-transformer (current-module)) exp)))
5161a3c0 485 '()))))