0.6.11.16:
[sbcl.git] / src / pcl / iterate.lisp
1 ;;;; This software is part of the SBCL system. See the README file for
2 ;;;; more information.
3
4 ;;;; This software is derived from software originally released by Xerox
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7 ;;;; absolutely no warranty. See the COPYING and CREDITS files for more
8 ;;;; information.
9
10 ;;;; copyright information from original PCL sources:
11 ;;;;
12 ;;;; Copyright (c) 1985, 1986, 1987, 1988, 1989, 1990 Xerox Corporation.
13 ;;;; All rights reserved.
14 ;;;;
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18 ;;;; control laws.
19 ;;;;
20 ;;;; This software is made available AS IS, and Xerox Corporation makes no
21 ;;;; warranty about the software, its performance or its conformity to any
22 ;;;; specification.
23
24 (in-package "SB-ITERATE")
25 \f
26 ;;; Are warnings to be issued for iterate/gather forms that aren't
27 ;;; optimized?
28 ;;;   NIL   => never
29 ;;;   :USER => those resulting from user code
30 ;;;   T     => always, even if it's the iteration macro that's suboptimal.
31 (defvar *iterate-warnings* :any)
32
33 ;;; ITERATE macro
34 (defmacro iterate (clauses &body body &environment env)
35   (optimize-iterate-form clauses body env))
36
37 ;;; temporary variable names used by ITERATE expansions
38 (defparameter *iterate-temp-vars-list*
39   '(iterate-temp-1 iterate-temp-2 iterate-temp-3 iterate-temp-4
40     iterate-temp-5 iterate-temp-6 iterate-temp-7 iterate-temp-8))
41
42 (defun
43  optimize-iterate-form
44  (clauses body iterate-env)
45  (let*
46   ((temp-vars *iterate-temp-vars-list*)
47    (block-name (gensym))
48    (finish-form `(return-from ,block-name))
49    (bound-vars (mapcan #'(lambda (clause)
50                                 (let ((names (first clause)))
51                                      (if (listp names)
52                                          (copy-list names)
53                                          (list names))))
54                       clauses))
55    iterate-decls generator-decls update-forms bindings leftover-body)
56   (do ((tail bound-vars (cdr tail)))
57       ((null tail))
58     ;; Check for duplicates
59     (when (member (car tail)
60                  (cdr tail))
61         (warn "Variable appears more than once in ITERATE: ~S" (car tail))))
62   (flet
63    ((get-iterate-temp nil
64
65            ;; Make temporary var. Note that it is ok to re-use these symbols
66            ;; in each iterate, because they are not used within BODY.
67            (or (pop temp-vars)
68                (gensym))))
69    (dolist (clause clauses)
70        (cond
71         ((or (not (consp clause))
72              (not (consp (cdr clause))))
73          (warn "bad syntax in ITERATE: clause not of form (var iterator): ~S"
74                clause))
75         (t
76          (unless (null (cddr clause))
77                 (warn
78        "probable parenthesis error in ITERATE clause--more than 2 elements: ~S"
79                       clause))
80          (multiple-value-bind
81           (let-body binding-type let-bindings localdecls otherdecls extra-body)
82           (expand-into-let (second clause)
83                  'iterate iterate-env)
84
85           ;; We have expanded the generator clause and parsed it into
86           ;; its LET pieces.
87           (prog*
88            ((vars (first clause))
89             gen-args renamed-vars)
90            (setq vars (if (listp vars)
91                           (copy-list vars)
92                           (list vars)))
93                                                ; VARS is now a (fresh) list of
94                                                ; all iteration vars bound in
95                                                ; this clause
96            (cond
97             ((eq let-body :abort)
98                                                ; Already issued a warning
99                                                ; about malformedness
100              )
101             ((null (setq let-body (function-lambda-p let-body 1)))
102                                                ; Not of the expected form
103              (let ((generator (second clause)))
104                   (cond ((and (consp generator)
105                               (fboundp (car generator)))
106                                                ; It looks ok--a macro or
107                                                ; function here--so the guy who
108                                                ; wrote it just didn't do it in
109                                                ; an optimizable way
110                          (maybe-warn :definition "could not optimize iterate clause ~S because generator not of form (LET[*] ... (FUNCTION (LAMBDA (finish) ...)))"
111                                 generator))
112                         (t                   ; Perhaps it's just a
113                                                ; misspelling?  Probably user
114                                                ; error
115                            (maybe-warn :user
116                                 "Iterate operator in clause ~S is not fboundp."
117                                 generator)))
118                   (setq let-body :abort)))
119             (t
120
121              ;; We have something of the form #'(LAMBDA (finisharg) ...),
122              ;; possibly with some LET bindings around it. LET-BODY =
123              ;; ((finisharg) ...).
124              (setq let-body (cdr let-body))
125              (setq gen-args (pop let-body))
126              (when let-bindings
127
128                  ;; The first transformation we want to perform is
129                  ;; "LET-eversion": turn (let* ((generator (let (..bindings..)
130                  ;; #'(lambda ...)))) ..body..) into (let* (..bindings..
131                  ;; (generator #'(lambda ...))) ..body..). This
132                  ;; transformation is valid if nothing in body refers to any
133                  ;; of the bindings, something we can ensure by
134                  ;; alpha-converting the inner let (substituting new names for
135                  ;; each var). Of course, none of those vars can be special,
136                  ;; but we already checked for that above.
137                  (multiple-value-setq (let-bindings renamed-vars)
138                         (rename-let-bindings let-bindings binding-type
139                                iterate-env leftover-body #'get-iterate-temp))
140                  (setq leftover-body nil)
141                                                ; If there was any leftover
142                                                ; from previous, it is now
143                                                ; consumed.
144                  )
145
146              ;; The second transformation is substituting the body of the
147              ;; generator (LAMBDA (finish-arg) . gen-body) for its appearance
148              ;; in the update form (funcall generator #'(lambda ()
149              ;; finish-form)), then simplifying that form. The requirement
150              ;; for this part is that the generator body not refer to any
151              ;; variables that are bound between the generator binding and the
152              ;; appearance in the loop body. The only variables bound in that
153              ;; interval are generator temporaries, which have unique names so
154              ;; are no problem, and the iteration variables remaining for
155              ;; subsequent clauses. We'll discover the story as we walk the
156              ;; body.
157              (multiple-value-bind (finishdecl other rest)
158                  (parse-declarations let-body gen-args)
159               (declare (ignore finishdecl))
160                                                ; Pull out declares, if any,
161                                                ; separating out the one(s)
162                                                ; referring to the finish arg,
163                                                ; which we will throw away.
164               (when other
165                                                ; Combine remaining decls with
166                                                ; decls extracted from the LET,
167                                                ; if any.
168                   (setq otherdecls (nconc otherdecls other)))
169               (setq let-body (cond
170                               (otherdecls
171                                                ; There are interesting
172                                                ; declarations, so have to keep
173                                                ; it wrapped.
174                                `(let nil (declare ,@otherdecls)
175                                      ,@rest))
176                               ((null (cdr rest))
177                                                ; Only one form left
178                                (first rest))
179                               (t `(progn ,@rest)))))
180              (unless (eq (setq let-body (iterate-transform-body let-body
181                                                iterate-env renamed-vars
182                                                (first gen-args)
183                                                finish-form bound-vars clause))
184                          :abort)
185
186                  ;; Skip the rest if transformation failed. Warning has
187                  ;; already been issued.
188
189                  ;; Note possible further optimization: if LET-BODY expanded
190                  ;; into (prog1 oldvalue prepare-for-next-iteration), as so
191                  ;; many do, then we could in most cases split the PROG1 into
192                  ;; two pieces: do the (setq var oldvalue) here, and do the
193                  ;; prepare-for-next-iteration at the bottom of the loop.
194                  ;; This does a slight optimization of the PROG1 and also
195                  ;; rearranges the code in a way that a reasonably clever
196                  ;; compiler might detect how to get rid of redundant
197                  ;; variables altogether (such as happens with INTERVAL and
198                  ;; LIST-TAILS); that would make the whole thing closer to
199                  ;; what you might have coded by hand. However, to do this
200                  ;; optimization, we need to ensure that (a) the
201                  ;; prepare-for-next-iteration refers freely to no vars other
202                  ;; than the internal vars we have extracted from the LET, and
203                  ;; (b) that the code has no side effects. These are both
204                  ;; true for all the iterators defined by this module, but how
205                  ;; shall we represent side-effect info and/or tap into the
206                  ;; compiler's knowledge of same?
207                  (when localdecls
208                                                ; There were declarations for
209                                                ; the generator locals--have to
210                                                ; keep them for later, and
211                                                ; rename the vars mentioned
212                      (setq
213                       generator-decls
214                       (nconc
215                        generator-decls
216                        (mapcar
217                         #'(lambda
218                            (decl)
219                            (let ((head (car decl)))
220                                 (cons head (if (eq head 'type)
221                                                (cons (second decl)
222                                                      (sublis renamed-vars
223                                                             (cddr decl)))
224                                                (sublis renamed-vars
225                                                       (cdr decl))))))
226                         localdecls)))))))
227
228            ;; Finished analyzing clause now. LET-BODY is the form which, when
229            ;; evaluated, returns updated values for the iteration variable(s)
230            ;; VARS.
231            (when (eq let-body :abort)
232
233                ;; Some punt case: go with the formal semantics: bind a var to
234                ;; the generator, then call it in the update section
235                (let
236                 ((gvar (get-iterate-temp))
237                  (generator (second clause)))
238                 (setq
239                  let-bindings
240                  (list (list gvar
241                              (cond
242                               ;; FIXME: This conditional was here with this
243                               ;; comment in old CMU CL PCL. Does Python really
244                               ;; think it's unreachable?
245                               ;;#-cmu ; Python thinks this is unreachable.
246                               (leftover-body
247                                                ; Have to use this up
248                                `(progn ,@(prog1 leftover-body (setq
249                                                                   leftover-body
250                                                                     nil))
251                                        generator))
252                               (t generator)))))
253                 (setq let-body `(funcall ,gvar #'(lambda nil ,finish-form)))))
254            (push (mv-setq (copy-list vars)
255                         let-body)
256                  update-forms)
257            (dolist (v vars)
258              (declare (ignore v))
259              ;; Pop off the vars we have now bound from the list of vars to
260              ;; watch out for -- we'll bind them right now.
261              (pop bound-vars))
262            (setq bindings
263                  (nconc bindings let-bindings
264                         (cond (extra-body
265                                ;; There was some computation to do after the
266                                ;; bindings--here's our chance.
267                                (cons (list (first vars)
268                                            `(progn ,@extra-body nil))
269                                      (rest vars)))
270                               (t vars))))))))))
271   (do ((tail body (cdr tail)))
272       ((not (and (consp tail)
273                  (consp (car tail))
274                  (eq (caar tail)
275                      'declare)))
276
277        ;; TAIL now points at first non-declaration. If there were
278        ;; declarations, pop them off so they appear in the right place
279        (unless (eq tail body)
280            (setq iterate-decls (ldiff body tail))
281            (setq body tail))))
282   `(block ,block-name
283        (let* ,bindings ,@(and generator-decls
284                               `((declare ,@generator-decls)))
285              ,@iterate-decls
286              ,@leftover-body
287              (loop ,@(nreverse update-forms)
288                    ,@body)))))
289
290 (defun expand-into-let (clause parent-name env)
291
292        ;; Return values: Body, LET[*], bindings, localdecls, otherdecls, extra
293        ;; body, where BODY is a single form. If multiple forms in a LET, the
294        ;; preceding forms are returned as extra body. Returns :ABORT if it
295        ;; issued a punt warning.
296        (prog ((expansion clause)
297               expandedp binding-type let-bindings let-body)
298              expand
299              (multiple-value-setq (expansion expandedp)
300                     (macroexpand-1 expansion env))
301              (cond ((not (consp expansion))
302                                                ; Shouldn't happen
303                     )
304                    ((symbolp (setq binding-type (first expansion)))
305                     (case binding-type
306                         ((let let*)
307                            (setq let-bindings (second expansion))
308                                                ; List of variable bindings
309                            (setq let-body (cddr expansion))
310                            (go handle-let))))
311                    ((and (consp binding-type)
312                          (eq (car binding-type)
313                              'lambda)
314                          (not (find-if #'(lambda (x)
315                                                 (member x lambda-list-keywords)
316                                                 )
317                                      (setq let-bindings (second binding-type)))
318                               )
319                          (eql (length (second expansion))
320                               (length let-bindings))
321                          (null (cddr expansion)))
322                                                ; A simple LAMBDA form can be
323                                                ; treated as LET
324                     (setq let-body (cddr binding-type))
325                     (setq let-bindings (mapcar #'list let-bindings (second
326                                                                     expansion))
327                           )
328                     (setq binding-type 'let)
329                     (go handle-let)))
330
331              ;; Fall thru if not a LET
332              (cond (expandedp             ; try expanding again
333                           (go expand))
334                    (t                     ; Boring--return form as the
335                                                ; body
336                       (return expansion)))
337              handle-let
338              (return (let ((locals (variables-from-let let-bindings))
339                            extra-body specials)
340                           (multiple-value-bind (localdecls otherdecls let-body)
341                               (parse-declarations let-body locals)
342                            (cond ((setq specials (extract-special-bindings
343                                                   locals localdecls))
344                                   (maybe-warn (cond ((find-if #'variable-globally-special-p
345                                                             specials)
346                                                ; This could be the fault of a
347                                                ; user proclamation.
348                                                      :user)
349                                                     (t :definition))
350
351           "Couldn't optimize ~S because expansion of ~S binds specials ~(~S ~)"
352                                          parent-name clause specials)
353                                   :abort)
354                                  (t (values (cond ((not (consp let-body))
355
356                                                ; Null body of LET?  unlikely,
357                                                ; but someone else will likely
358                                                ; complain
359                                                    nil)
360                                                   ((null (cdr let-body))
361
362                                                ; A single expression, which we
363                                                ; hope is (function
364                                                ; (lambda...))
365                                                    (first let-body))
366                                                   (t
367
368                           ;; More than one expression. These are forms to
369                           ;; evaluate after the bindings but before the
370                           ;; generator form is returned. Save them to
371                           ;; evaluate in the next convenient place. Note that
372                           ;; this is ok, as there is no construct that can
373                           ;; cause a LET to return prematurely (without
374                           ;; returning also from some surrounding construct).
375                                                      (setq extra-body
376                                                            (butlast let-body))
377                                                      (car (last let-body))))
378                                            binding-type let-bindings localdecls
379                                            otherdecls extra-body))))))))
380
381 (defun variables-from-let (bindings)
382
383        ;; Return a list of the variables bound in the first argument to LET[*].
384        (mapcar #'(lambda (binding)
385                         (if (consp binding)
386                             (first binding)
387                             binding))
388               bindings))
389
390 (defun iterate-transform-body (let-body iterate-env renamed-vars finish-arg
391                                      finish-form bound-vars clause)
392
393 ;;; This is the second major transformation for a single iterate clause.
394 ;;; LET-BODY is the body of the iterator after we have extracted its local
395 ;;; variables and declarations. We have two main tasks: (1) Substitute
396 ;;; internal temporaries for occurrences of the LET variables; the alist
397 ;;; RENAMED-VARS specifies this transformation. (2) Substitute evaluation of
398 ;;; FINISH-FORM for any occurrence of (funcall FINISH-ARG). Along the way, we
399 ;;; check for forms that would invalidate these transformations: occurrence of
400 ;;; FINISH-ARG outside of a funcall, and free reference to any element of
401 ;;; BOUND-VARS. CLAUSE & TYPE are the original ITERATE clause and its type
402 ;;; (ITERATE or ITERATE*), for purpose of error messages. On success, we
403 ;;; return the transformed body; on failure, :ABORT.
404
405        (walk-form let-body iterate-env
406               #'(lambda (form context env)
407                        (declare (ignore context))
408
409                        ;; Need to substitute RENAMED-VARS, as well as turn
410                        ;; (FUNCALL finish-arg) into the finish form
411                        (cond ((symbolp form)
412                               (let (renaming)
413                                    (cond ((and (eq form finish-arg)
414                                                (variable-same-p form env
415                                                       iterate-env))
416                                                ; An occurrence of the finish
417                                                ; arg outside of FUNCALL
418                                                ; context--I can't handle this
419                                           (maybe-warn :definition "Couldn't optimize iterate form because generator ~S does something with its FINISH arg besides FUNCALL it."
420                                                  (second clause))
421                                           (return-from iterate-transform-body
422                                                  :abort))
423                                          ((and (setq renaming (assoc form
424                                                                    renamed-vars
425                                                                      ))
426                                                (variable-same-p form env
427                                                       iterate-env))
428                                                ; Reference to one of the vars
429                                                ; we're renaming
430                                           (cdr renaming))
431                                          ((and (member form bound-vars)
432                                                (variable-same-p form env
433                                                       iterate-env))
434                                                ; FORM is a var that is bound
435                                                ; in this same ITERATE, or
436                                                ; bound later in this ITERATE*.
437                                                ; This is a conflict.
438                                           (maybe-warn :user "Couldn't optimize iterate form because generator ~S is closed over ~S, in conflict with a subsequent iteration variable."
439                                                  (second clause)
440                                                  form)
441                                           (return-from iterate-transform-body
442                                                  :abort))
443                                          (t form))))
444                              ((and (consp form)
445                                    (eq (first form)
446                                        'funcall)
447                                    (eq (second form)
448                                        finish-arg)
449                                    (variable-same-p (second form)
450                                           env iterate-env))
451                                                ; (FUNCALL finish-arg) =>
452                                                ; finish-form
453                               (unless (null (cddr form))
454                                   (maybe-warn :definition
455         "Generator for ~S applied its finish arg to > 0 arguments ~S--ignored."
456                                          (second clause)
457                                          (cddr form)))
458                               finish-form)
459                              (t form)))))
460
461 (defun
462  parse-declarations
463  (tail locals)
464
465  ;; Extract the declarations from the head of TAIL and divide them into 2
466  ;; classes: declares about variables in the list LOCALS, and all other
467  ;; declarations. Returns 3 values: those 2 lists plus the remainder of TAIL.
468  (let
469   (localdecls otherdecls form)
470   (loop
471    (unless (and tail (consp (setq form (car tail)))
472                 (eq (car form)
473                     'declare))
474        (return (values localdecls otherdecls tail)))
475    (mapc
476     #'(lambda
477        (decl)
478        (case (first decl)
479            ((inline notinline optimize)
480                                                ; These don't talk about vars
481               (push decl otherdecls))
482            (t                             ; Assume all other kinds are
483                                                ; for vars
484               (let* ((vars (if (eq (first decl)
485                                    'type)
486                                (cddr decl)
487                                (cdr decl)))
488                      (l (intersection locals vars))
489                      other)
490                     (cond
491                      ((null l)
492                                                ; None talk about LOCALS
493                       (push decl otherdecls))
494                      ((null (setq other (set-difference vars l)))
495                                                ; All talk about LOCALS
496                       (push decl localdecls))
497                      (t                 ; Some of each
498                         (let ((head (cons 'type (and (eq (first decl)
499                                                          'type)
500                                                      (list (second decl))))))
501                              (push (append head other)
502                                    otherdecls)
503                              (push (append head l)
504                                    localdecls))))))))
505     (cdr form))
506    (pop tail))))
507
508 (defun extract-special-bindings (vars decls)
509
510        ;; Return the subset of VARS that are special, either globally or
511        ;; because of a declaration in DECLS
512        (let ((specials (remove-if-not #'variable-globally-special-p vars)))
513             (dolist (d decls)
514                 (when (eq (car d)
515                           'special)
516                     (setq specials (union specials (intersection vars
517                                                           (cdr d))))))
518             specials))
519
520 (defun function-lambda-p (form &optional nargs)
521
522        ;; If FORM is #'(LAMBDA bindings . body) and bindings is of length
523        ;; NARGS, return the lambda expression
524        (let (args body)
525             (and (consp form)
526                  (eq (car form)
527                      'function)
528                  (consp (setq form (cdr form)))
529                  (null (cdr form))
530                  (consp (setq form (car form)))
531                  (eq (car form)
532                      'lambda)
533                  (consp (setq body (cdr form)))
534                  (listp (setq args (car body)))
535                  (or (null nargs)
536                      (eql (length args)
537                           nargs))
538                  form)))
539
540 (defun
541  rename-let-bindings
542  (let-bindings binding-type env leftover-body &optional tempvarfn)
543
544  ;; Perform the alpha conversion required for "LET eversion" of
545  ;; (LET[*] LET-BINDINGS . body)--rename each of the variables to an
546  ;; internal name. Returns 2 values: a new set of LET bindings and the
547  ;; alist of old var names to new (so caller can walk the body doing
548  ;; the rest of the renaming). BINDING-TYPE is one of LET or LET*.
549  ;; LEFTOVER-BODY is optional list of forms that must be eval'ed
550  ;; before the first binding happens. ENV is the macro expansion
551  ;; environment, in case we have to walk a LET*. TEMPVARFN is a
552  ;; function of no args to return a temporary var; if omitted, we use
553  ;; GENSYM.
554  (let
555   (renamed-vars)
556   (values (mapcar #'(lambda (binding)
557                            (let ((valueform (cond ((not (consp binding))
558
559                                                ; No initial value
560                                                    nil)
561                                                   ((or (eq binding-type
562                                                            'let)
563                                                        (null renamed-vars))
564
565                                                ; All bindings are in parallel,
566                                                ; so none can refer to others
567                                                    (second binding))
568                                                   (t
569                                                ; In a LET*, have to substitute
570                                                ; vars in the 2nd and
571                                                ; subsequent initialization
572                                                ; forms
573                                                      (rename-variables
574                                                       (second binding)
575                                                       renamed-vars env))))
576                                  (newvar (if tempvarfn
577                                              (funcall tempvarfn)
578                                              (gensym))))
579                                 (push (cons (if (consp binding)
580                                                 (first binding)
581                                                 binding)
582                                             newvar)
583                                       renamed-vars)
584                                                ; Add new variable to the list
585                                                ; AFTER we have walked the
586                                                ; initial value form
587                                 (when leftover-body
588                                   ;; Previous clause had some computation to do
589                                   ;; after its bindings. Here is the first
590                                   ;; opportunity to do it
591                                   (setq valueform `(progn ,@leftover-body
592                                                           ,valueform))
593                                   (setq leftover-body nil))
594                                 (list newvar valueform)))
595                  let-bindings)
596          renamed-vars)))
597
598 (defun rename-variables (form alist env)
599
600        ;; Walks FORM, renaming occurrences of the key variables in ALIST with
601        ;; their corresponding values. ENV is FORM's environment, so we can
602        ;; make sure we are talking about the same variables.
603        (walk-form form env
604               #'(lambda (form context subenv)
605                        (declare (ignore context))
606                        (let (pair)
607                             (cond ((and (symbolp form)
608                                         (setq pair (assoc form alist))
609                                         (variable-same-p form subenv env))
610                                    (cdr pair))
611                                   (t form))))))
612
613 (defun
614  mv-setq
615  (vars expr)
616
617  ;; Produces (MULTIPLE-VALUE-SETQ vars expr), except that I'll optimize some
618  ;; of the simple cases for benefit of compilers that don't, and I don't care
619  ;; what the value is, and I know that the variables need not be set in
620  ;; parallel, since they can't be used free in EXPR
621  (cond
622   ((null vars)
623                                                ; EXPR is a side-effect
624    expr)
625   ((not (consp vars))
626                                                ; This is an error, but I'll
627                                                ; let MULTIPLE-VALUE-SETQ
628                                                ; report it
629    `(multiple-value-setq ,vars ,expr))
630   ((and (listp expr)
631         (eq (car expr)
632             'values))
633
634    ;; (mv-setq (a b c) (values x y z)) can be reduced to a parallel setq
635    ;; (psetq returns nil, but I don't care about returned value). Do this
636    ;; even for the single variable case so that we catch (mv-setq (a) (values
637    ;; x y))
638    (pop expr)
639                                                ; VALUES
640    `(setq ,@(mapcon #'(lambda (tail)
641                              (list (car tail)
642                                    (cond ((or (cdr tail)
643                                               (null (cdr expr)))
644                                                ; One result expression for
645                                                ; this var
646                                           (pop expr))
647                                          (t    ; More expressions than vars,
648                                                ; so arrange to evaluate all
649                                                ; the rest now.
650                                             (cons 'prog1 expr)))))
651                    vars)))
652   ((null (cdr vars))
653                                                ; Simple one variable case
654    `(setq ,(car vars)
655           ,expr))
656   (t                                       ; General case--I know nothing
657      `(multiple-value-setq ,vars ,expr))))
658
659 (defun variable-same-p (var env1 env2)
660        (eq (variable-lexical-p var env1)
661            (variable-lexical-p var env2)))
662
663 (defun maybe-warn (type &rest warn-args)
664
665        ;; Issue a warning about not being able to optimize this thing. TYPE
666        ;; is one of :DEFINITION, meaning the definition is at fault, and
667        ;; :USER, meaning the user's code is at fault.
668        (when (case *iterate-warnings*
669                  ((nil) nil)
670                  ((:user) (eq type :user))
671                  (t t))
672            (apply #'warn warn-args)))
673
674 ;;; sample iterators
675 ;;;
676 ;;; FIXME: If they're only samples, can they be commented out?
677
678 (defmacro
679  interval
680  (&whole whole &key from downfrom to downto above below by type)
681  (cond
682   ((and from downfrom)
683    (error "Can't use both FROM and DOWNFROM in ~S" whole))
684   ((cdr (remove nil (list to downto above below)))
685    (error "Can't use more than one limit keyword in ~S" whole))
686   (t
687    (let*
688     ((down (or downfrom downto above))
689      (limit (or to downto above below))
690      (inc (cond ((null by)
691                  1)
692                 ((constantp by)
693                                                ; Can inline this increment
694                  by))))
695     `(let
696       ((from ,(or from downfrom 0))
697        ,@(and limit `((to ,limit)))
698        ,@(and (null inc)
699               `((by ,by))))
700       ,@(and type `((declare (type ,type from ,@(and limit '(to))
701                                    ,@(and (null inc)
702                                           `(by))))))
703       #'(lambda
704          (finish)
705          ,@(cond ((null limit)
706                                                ; We won't use the FINISH arg.
707                   '((declare (ignore finish)))))
708          (prog1 ,(cond (limit             ; Test the limit. If ok,
709                                                ; return current value and
710                                                ; increment, else quit
711                               `(if (,(cond (above '>)
712                                            (below '<)
713                                            (down '>=)
714                                            (t '<=))
715                                     from to)
716                                    from
717                                    (funcall finish)))
718                        (t                     ; No test
719                           'from))
720              (setq from (,(if down
721                               '-
722                               '+)
723                          from
724                          ,(or inc 'by))))))))))
725
726 (defmacro list-elements (list &key (by '#'cdr))
727        `(let ((tail ,list))
728              #'(lambda (finish)
729                       (prog1 (if (endp tail)
730                                  (funcall finish)
731                                  (first tail))
732                           (setq tail (funcall ,by tail))))))
733
734 (defmacro list-tails (list &key (by '#'cdr))
735        `(let ((tail ,list))
736              #'(lambda (finish)
737                       (prog1 (if (endp tail)
738                                  (funcall finish)
739                                  tail)
740                           (setq tail (funcall ,by tail))))))
741
742 (defmacro
743  elements
744  (sequence)
745  "Generates successive elements of SEQUENCE, with second value being the index. Use (ELEMENTS (THE type arg)) if you care about the type."
746  (let*
747   ((type (and (consp sequence)
748               (eq (first sequence)
749                   'the)
750               (second sequence)))
751    (accessor (if type
752                  (sequence-accessor type)
753                  'elt))
754    (listp (eq type 'list)))
755
756   ;; If type is given via THE, we may be able to generate a good accessor here
757   ;; for the benefit of implementations that aren't smart about (ELT (THE
758   ;; STRING FOO)). I'm not bothering to keep the THE inside the body,
759   ;; however, since I assume any compiler that would understand (AREF (THE
760   ;; SIMPLE-ARRAY S)) would also understand that (AREF S) is the same when I
761   ;; bound S to (THE SIMPLE-ARRAY foo) and never modified it.
762
763   ;; If sequence is declared to be a list, it's better to cdr down it, so we
764   ;; have some extra cases here. Normally folks would write LIST-ELEMENTS,
765   ;; but maybe they wanted to get the index for free...
766   `(let* ((index 0)
767           (s ,sequence)
768           ,@(and (not listp)
769                  '((size (length s)))))
770          #'(lambda (finish)
771                   (values (cond ,(if listp
772                                      '((not (endp s))
773                                        (pop s))
774                                      `((< index size)
775                                        (,accessor s index)))
776                                 (t (funcall finish)))
777                          (prog1 index
778                              (setq index (1+ index))))))))
779
780 (defmacro
781  plist-elements
782  (plist)
783  "Generates each time 2 items, the indicator and the value."
784  `(let ((tail ,plist))
785        #'(lambda (finish)
786                 (values (if (endp tail)
787                             (funcall finish)
788                             (first tail))
789                        (prog1 (if (endp (setq tail (cdr tail)))
790                                   (funcall finish)
791                                   (first tail))
792                            (setq tail (cdr tail)))))))
793
794 (defun sequence-accessor (type)
795
796        ;; returns the function with which most efficiently to make accesses to
797        ;; a sequence of type TYPE.
798        (case (if (consp type)
799                                                ; e.g., (VECTOR FLOAT *)
800                  (car type)
801                  type)
802            ((array simple-array vector) 'aref)
803            (simple-vector 'svref)
804            (string 'char)
805            (simple-string 'schar)
806            (bit-vector 'bit)
807            (simple-bit-vector 'sbit)
808            (t 'elt)))
809
810 ;; These "iterators" may be withdrawn
811
812 (defmacro eachtime (expr)
813        `#'(lambda (finish)
814                  (declare (ignore finish))
815                  ,expr))
816
817 (defmacro while (expr)
818        `#'(lambda (finish)
819                  (unless ,expr (funcall finish))))
820
821 (defmacro until (expr)
822        `#'(lambda (finish)
823                  (when ,expr (funcall finish))))
824
825                                                ; GATHERING macro
826
827 (defmacro gathering (clauses &body body &environment env)
828        (or (optimize-gathering-form clauses body env)
829            (simple-expand-gathering-form clauses body env)))
830
831 (defmacro with-gathering (clauses gather-body &body use-body)
832        "Binds the variables specified in CLAUSES to the result of (GATHERING clauses gather-body) and evaluates the forms in USE-BODY inside that contour."
833
834        ;; We may optimize this a little better later for those compilers that
835        ;; don't do a good job on (m-v-bind vars (... (values ...)) ...).
836        `(multiple-value-bind ,(mapcar #'car clauses)
837                (gathering ,clauses ,gather-body)
838                ,@use-body))
839
840 (defun
841  simple-expand-gathering-form
842  (clauses body env)
843  (declare (ignore env))
844
845  ;; The "formal semantics" of GATHERING. We use this only in cases that can't
846  ;; be optimized.
847  (let
848   ((acc-names (mapcar #'first (if (symbolp clauses)
849                                                ; Shorthand using anonymous
850                                                ; gathering site
851                                   (setq clauses `((*anonymous-gathering-site*
852                                                    (,clauses))))
853                                   clauses)))
854    (realizer-names (mapcar #'(lambda (binding)
855                                     (declare (ignore binding))
856                                     (gensym))
857                           clauses)))
858   `(multiple-value-call
859     #'(lambda
860        ,(mapcan #'list acc-names realizer-names)
861        (flet ((gather (value &optional (accumulator *anonymous-gathering-site*)
862                              )
863                      (funcall accumulator value)))
864              ,@body
865              (values ,@(mapcar #'(lambda (rname)
866                                         `(funcall ,rname))
867                               realizer-names))))
868     ,@(mapcar #'second clauses))))
869
870 (defvar *active-gatherers* nil
871        "List of GATHERING bindings currently active during macro expansion)")
872
873 (defvar *anonymous-gathering-site* nil "Variable used in formal expansion of an abbreviated GATHERING form (one with anonymous gathering site).")
874
875 (defun optimize-gathering-form (clauses body gathering-env)
876  (let*
877   (acc-info leftover-body top-bindings finish-forms top-decls)
878   (dolist (clause (if (symbolp clauses)
879                                                ; a shorthand
880                       `((*anonymous-gathering-site* (,clauses)))
881                       clauses))
882       (multiple-value-bind
883        (let-body binding-type let-bindings localdecls otherdecls extra-body)
884        (expand-into-let (second clause)
885               'gathering gathering-env)
886        (prog*
887         ((acc-var (first clause))
888          renamed-vars accumulator realizer)
889         (when (and (consp let-body)
890                    (eq (car let-body)
891                        'values)
892                    (consp (setq let-body (cdr let-body)))
893                    (setq accumulator (function-lambda-p (car let-body)))
894                    (consp (setq let-body (cdr let-body)))
895                    (setq realizer (function-lambda-p (car let-body)
896                                          0))
897                    (null (cdr let-body)))
898
899             ;; Macro returned something of the form
900             ;;   (VALUES #'(lambda (value) ...)
901             ;;     #'(lambda () ...)),
902             ;; a function to accumulate values and a function to realize the
903             ;; result.
904             (when binding-type
905
906                 ;; Gatherer expanded into a LET
907                 (cond (otherdecls (maybe-warn :definition "Couldn't optimize GATHERING clause ~S because its expansion carries declarations about more than the bound variables: ~S"
908                                          (second clause)
909                                          `(declare ,@otherdecls))
910                              (go punt)))
911                 (when let-bindings
912
913                     ;; The first transformation we want to perform is a
914                     ;; variant of "LET-eversion": turn
915                     ;;   (mv-bind
916                     ;;       (acc real)
917                     ;;       (let (..bindings..)
918                     ;;   (values #'(lambda ...)
919                     ;;           #'(lambda ...)))
920                     ;;     ..body..)
921                     ;; into
922                     ;;   (let* (..bindings..
923                     ;;    (acc #'(lambda ...))
924                     ;;    (real #'(lambda ...)))
925                     ;;     ..body..).
926                     ;; This transformation is valid if nothing in body refers
927                     ;; to any of the bindings, something we can ensure by
928                     ;; alpha-converting the inner let (substituting new names
929                     ;; for each var). Of course, none of those vars can be
930                     ;; special, but we already checked for that above.
931                     (multiple-value-setq (let-bindings renamed-vars)
932                            (rename-let-bindings let-bindings binding-type
933                                   gathering-env leftover-body))
934                     (setq top-bindings (nconc top-bindings let-bindings))
935                     (setq leftover-body nil)
936                                                ; If there was any leftover
937                                                ; from previous, it is now
938                                                ; consumed
939                     ))
940             (setq leftover-body (nconc leftover-body extra-body))
941                                                ; Computation to do after these
942                                                ; bindings
943             (push (cons acc-var (rename-and-capture-variables accumulator
944                                        renamed-vars gathering-env))
945                   acc-info)
946             (setq realizer (rename-variables realizer renamed-vars
947                                   gathering-env))
948             (push (cond ((null (cdddr realizer))
949                                                ; Simple (LAMBDA () expr) =>
950                                                ; expr
951                          (third realizer))
952                         (t                   ; There could be declarations
953                                                ; or something, so leave as a
954                                                ; LET
955                            (cons 'let (cdr realizer))))
956                   finish-forms)
957             (unless (null localdecls)
958                                                ; Declarations about the LET
959                                                ; variables also has to
960                                                ; percolate up
961                 (setq top-decls (nconc top-decls (sublis renamed-vars
962                                                         localdecls))))
963             (return))
964         (maybe-warn :definition "Couldn't optimize GATHERING clause ~S because its expansion is not of the form (VALUES #'(LAMBDA ...) #'(LAMBDA () ...))"
965                (second clause))
966         punt
967         (let
968          ((gs (gensym))
969           (expansion `(multiple-value-list ,(second clause))))
970                                                ; Slow way--bind gensym to the
971                                                ; macro expansion, and we will
972                                                ; funcall it in the body
973          (push (list acc-var gs)
974                acc-info)
975          (push `(funcall (cadr ,gs))
976                finish-forms)
977          (setq
978           top-bindings
979           (nconc
980            top-bindings
981            (list (list gs (cond (leftover-body
982                                  `(progn ,@(prog1 leftover-body
983                                                   (setq leftover-body nil))
984                                          ,expansion))
985                                 (t expansion))))))))))
986   (setq body (walk-gathering-body body gathering-env acc-info))
987   (cond ((eq body :abort)
988                                                ; Couldn't finish expansion
989          nil)
990         (t `(let* ,top-bindings
991                   ,@(and top-decls `((declare ,@top-decls)))
992                   ,body
993                   ,(cond ((null (cdr finish-forms))
994                                                ; just a single value
995                           (car finish-forms))
996                          (t `(values ,@(reverse finish-forms)))))))))
997
998 (defun rename-and-capture-variables (form alist env)
999
1000        ;; Walks FORM, renaming occurrences of the key variables in ALIST with
1001        ;; their corresponding values, and capturing any other free variables.
1002        ;; Returns a list of the new form and the list of other closed-over
1003        ;; vars. ENV is FORM's environment, so we can make sure we are talking
1004        ;; about the same variables.
1005        (let (closed)
1006             (list (walk-form
1007                    form env
1008                    #'(lambda (form context subenv)
1009                             (declare (ignore context))
1010                             (let (pair)
1011                                  (cond ((or (not (symbolp form))
1012                                             (not (variable-same-p form subenv
1013                                                         env)))
1014                                                ; non-variable or one that has
1015                                                ; been rebound
1016                                         form)
1017                                        ((setq pair (assoc form alist))
1018                                                ; One to rename
1019                                         (cdr pair))
1020                                        (t      ; var is free
1021                                           (pushnew form closed)
1022                                           form)))))
1023                   closed)))
1024
1025 (defun
1026  walk-gathering-body
1027  (body gathering-env acc-info)
1028
1029  ;; Walk the body of (GATHERING (...) . BODY) in environment GATHERING-ENV.
1030  ;; ACC-INFO is a list of information about each of the gathering "bindings"
1031  ;; in the form, in the form (var gatheringfn freevars env)
1032  (let
1033   ((*active-gatherers* (nconc (mapcar #'car acc-info)
1034                               *active-gatherers*)))
1035
1036   ;; *ACTIVE-GATHERERS* tells us what vars are currently legal as GATHER
1037   ;; targets. This is so that when we encounter a GATHER not belonging to us
1038   ;; we can know whether to warn about it.
1039   (walk-form
1040    (cons 'progn body)
1041    gathering-env
1042    #'(lambda
1043       (form context env)
1044       (declare (ignore context))
1045       (let (info site)
1046            (cond ((consp form)
1047                   (cond
1048                    ((not (eq (car form)
1049                              'gather))
1050                                                ; We only care about GATHER
1051                     (when (and (eq (car form)
1052                                    'function)
1053                                (eq (cadr form)
1054                                    'gather))
1055                                                ; Passed as functional--can't
1056                                                ; macroexpand
1057                         (maybe-warn :user
1058                    "Can't optimize GATHERING because of reference to #'GATHER."
1059                                )
1060                         (return-from walk-gathering-body :abort))
1061                     form)
1062                    ((setq info (assoc (setq site (if (null (cddr form))
1063
1064                                                      '
1065                                                      *anonymous-gathering-site*
1066                                                      (third form)))
1067                                       acc-info))
1068                                                ; One of ours--expand (GATHER
1069                                                ; value var). INFO = (var
1070                                                ; gatheringfn freevars env)
1071                     (unless (null (cdddr form))
1072                            (warn "Extra arguments (> 2) in ~S discarded." form)
1073                            )
1074                     (let ((fn (second info)))
1075                          (cond ((symbolp fn)
1076                                                ; Unoptimized case--just call
1077                                                ; the gatherer. FN is the
1078                                                ; gensym that we bound to the
1079                                                ; list of two values returned
1080                                                ; from the gatherer.
1081                                 `(funcall (car ,fn)
1082                                         ,(second form)))
1083                                (t             ; FN = (lambda (value) ...)
1084                                   (dolist (s (third info))
1085                                       (unless (or (variable-same-p s env
1086                                                          gathering-env)
1087                                                   (and (variable-special-p
1088                                                         s env)
1089                                                        (variable-special-p
1090                                                         s gathering-env)))
1091
1092                           ;; Some var used free in the LAMBDA form has been
1093                           ;; rebound between here and the parent GATHERING
1094                           ;; form, so can't substitute the lambda. Ok if it's
1095                           ;; a special reference both here and in the LAMBDA,
1096                           ;; because then it's not closed over.
1097                                           (maybe-warn :user "Can't optimize GATHERING because the expansion closes over the variable ~S, which is rebound around a GATHER for it."
1098                                                  s)
1099                                           (return-from walk-gathering-body
1100                                                  :abort)))
1101
1102                           ;; Return ((lambda (value) ...) actual-value). In
1103                           ;; many cases we could simplify this further by
1104                           ;; substitution, but we'd have to be careful (for
1105                           ;; example, we would need to alpha-convert any LET
1106                           ;; we found inside). Any decent compiler will do it
1107                           ;; for us.
1108                                   (list fn (second form))))))
1109                    ((and (setq info (member site *active-gatherers*))
1110                          (or (eq site '*anonymous-gathering-site*)
1111                              (variable-same-p site env (fourth info))))
1112                                                ; Some other GATHERING will
1113                                                ; take care of this form, so
1114                                                ; pass it up for now.
1115                                                ; Environment check is to make
1116                                                ; sure nobody shadowed it
1117                                                ; between here and there
1118                     form)
1119                    (t                     ; Nobody's going to handle it
1120                       (if (eq site '*anonymous-gathering-site*)
1121                                                ; More likely that she forgot
1122                                                ; to mention the site than
1123                                                ; forget to write an anonymous
1124                                                ; gathering.
1125                           (warn "There is no gathering site specified in ~S."
1126                                 form)
1127                           (warn
1128              "The site ~S in ~S is not defined in an enclosing GATHERING form."
1129                                 site form))
1130                                                ; Turn it into something else
1131                                                ; so we don't warn twice in the
1132                                                ; nested case
1133                       `(%orphaned-gather ,@(cdr form)))))
1134                  ((and (symbolp form)
1135                        (setq info (assoc form acc-info))
1136                        (variable-same-p form env gathering-env))
1137                                                ; A variable reference to a
1138                                                ; gather binding from
1139                                                ; environment TEM
1140                   (maybe-warn :user "Can't optimize GATHERING because site variable ~S is used outside of a GATHER form."
1141                          form)
1142                   (return-from walk-gathering-body :abort))
1143                  (t form)))))))
1144
1145 ;; sample gatherers
1146 ;;
1147 ;; FIXME: If these are only samples, can we delete them?
1148
1149 (defmacro
1150  collecting
1151  (&key initial-value)
1152  `(let* ((head ,initial-value)
1153          (tail ,(and initial-value `(last head))))
1154         (values #'(lambda (value)
1155                          (if (null head)
1156                              (setq head (setq tail (list value)))
1157                              (setq tail (cdr (rplacd tail (list value))))))
1158                #'(lambda nil head))))
1159
1160 (defmacro joining (&key initial-value)
1161        `(let ((result ,initial-value))
1162              (values #'(lambda (value)
1163                               (setq result (nconc result value)))
1164                     #'(lambda nil result))))
1165
1166 (defmacro
1167  maximizing
1168  (&key initial-value)
1169  `(let ((result ,initial-value))
1170        (values
1171         #'(lambda (value)
1172                  (when ,(cond ((and (constantp initial-value)
1173                                     (not (null (eval initial-value))))
1174                                                ; Initial value is given and we
1175                                                ; know it's not NIL, so leave
1176                                                ; out the null check
1177                                '(> value result))
1178                               (t '(or (null result)
1179                                       (> value result))))
1180                        (setq result value)))
1181         #'(lambda nil result))))
1182
1183 (defmacro
1184  minimizing
1185  (&key initial-value)
1186  `(let ((result ,initial-value))
1187        (values
1188         #'(lambda (value)
1189                  (when ,(cond ((and (constantp initial-value)
1190                                     (not (null (eval initial-value))))
1191                                                ; Initial value is given and we
1192                                                ; know it's not NIL, so leave
1193                                                ; out the null check
1194                                '(< value result))
1195                               (t '(or (null result)
1196                                       (< value result))))
1197                        (setq result value)))
1198         #'(lambda nil result))))
1199
1200 (defmacro summing (&key (initial-value 0))
1201        `(let ((sum ,initial-value))
1202              (values #'(lambda (value)
1203                               (setq sum (+ sum value)))
1204                     #'(lambda nil sum))))
1205
1206 ;;; It's easier to read expanded code if PROG1 gets left alone.
1207 (define-walker-template prog1 (nil return sb-walker::repeat (eval)))