1: \ A powerful locals implementation
2:
3: \ Copyright (C) 1995,1996,1997,1998,2000,2003,2004,2005,2007,2011 Free Software Foundation, Inc.
4:
5: \ This file is part of Gforth.
6:
7: \ Gforth is free software; you can redistribute it and/or
8: \ modify it under the terms of the GNU General Public License
9: \ as published by the Free Software Foundation, either version 3
10: \ of the License, or (at your option) any later version.
11:
12: \ This program is distributed in the hope that it will be useful,
13: \ but WITHOUT ANY WARRANTY; without even the implied warranty of
14: \ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15: \ GNU General Public License for more details.
16:
17: \ You should have received a copy of the GNU General Public License
18: \ along with this program. If not, see http://www.gnu.org/licenses/.
19:
20:
21: \ More documentation can be found in the manual and in
22: \ http://www.complang.tuwien.ac.at/papers/ertl94l.ps.gz
23:
24: \ Local variables are quite important for writing readable programs, but
25: \ IMO (anton) they are the worst part of the standard. There they are very
26: \ restricted and have an ugly interface.
27:
28: \ So, we implement the locals wordset, but do not recommend using
29: \ locals-ext (which is a really bad user interface for locals).
30:
31: \ We also have a nice and powerful user-interface for locals: locals are
32: \ defined with
33:
34: \ { local1 local2 ... }
35: \ or
36: \ { local1 local2 ... -- ... }
37: \ (anything after the -- is just a comment)
38:
39: \ Every local in this list consists of an optional type specification
40: \ and a name. If there is only the name, it stands for a cell-sized
41: \ value (i.e., you get the value of the local variable, not it's
42: \ address). The following type specifiers stand before the name:
43:
44: \ Specifier Type Access
45: \ W: Cell value
46: \ W^ Cell address
47: \ D: Double value
48: \ D^ Double address
49: \ F: Float value
50: \ F^ Float address
51: \ C: Char value
52: \ C^ Char address
53:
54: \ The local variables are initialized with values from the appropriate
55: \ stack. In contrast to the examples in the standard document our locals
56: \ take the arguments in the expected way: The last local gets the top of
57: \ stack, the second last gets the second stack item etc. An example:
58:
59: \ : CX* { F: Ar F: Ai F: Br F: Bi -- Cr Ci }
60: \ \ complex multiplication
61: \ Ar Br f* Ai Bi f* f-
62: \ Ar Bi f* Ai Br f* f+ ;
63:
64: \ There will also be a way to add user types, but it is not yet decided,
65: \ how. Ideas are welcome.
66:
67: \ Locals defined in this manner live until (!! see below).
68: \ Their names can be used during this time to get
69: \ their value or address; The addresses produced in this way become
70: \ invalid at the end of the lifetime.
71:
72: \ Values can be changed with TO, but this is not recomended (TO is a
73: \ kludge and words lose the single-assignment property, which makes them
74: \ harder to analyse).
75:
76: \ As for the internals, we use a special locals stack. This eliminates
77: \ the problems and restrictions of reusing the return stack and allows
78: \ to store floats as locals: the return stack is not guaranteed to be
79: \ aligned correctly, but our locals stack must be float-aligned between
80: \ words.
81:
82: \ Other things about the internals are pretty unclear now.
83:
84: \ Currently locals may only be
85: \ defined at the outer level and TO is not supported.
86:
87: require search.fs
88: require float.fs
89: require extend.fs \ for case
90:
91: : compile-@local ( n -- ) \ gforth compile-fetch-local
92: case
93: 0 of postpone @local0 endof
94: 1 cells of postpone @local1 endof
95: 2 cells of postpone @local2 endof
96: 3 cells of postpone @local3 endof
97: ( otherwise ) dup postpone @local# ,
98: endcase ;
99:
100: : compile-f@local ( n -- ) \ gforth compile-f-fetch-local
101: case
102: 0 of postpone f@local0 endof
103: 1 floats of postpone f@local1 endof
104: ( otherwise ) dup postpone f@local# ,
105: endcase ;
106:
107: \ locals stuff needed for control structures
108:
109: : compile-lp+! ( n -- ) \ gforth compile-l-p-plus-store
110: dup negate locals-size +!
111: 0 over = if
112: else -1 cells over = if postpone lp-
113: else 1 floats over = if postpone lp+
114: else 2 floats over = if postpone lp+2
115: else postpone lp+!# dup ,
116: then then then then drop ;
117:
118: : adjust-locals-size ( n -- ) \ gforth
119: \ sets locals-size to n and generates an appropriate lp+!
120: locals-size @ swap - compile-lp+! ;
121:
122: \ the locals stack grows downwards (see primitives)
123: \ of the local variables of a group (in braces) the leftmost is on top,
124: \ i.e. by going onto the locals stack the order is reversed.
125: \ there are alignment gaps if necessary.
126: \ lp must have the strictest alignment (usually float) across calls;
127: \ for simplicity we align it strictly for every group.
128:
129: slowvoc @
130: slowvoc on \ we want a linked list for the vocabulary locals
131: vocabulary locals \ this contains the local variables
132: ' locals >body wordlist-id ' locals-list >body !
133: slowvoc !
134:
135: variable locals-mem-list \ linked list of all locals name memory in
136: 0 locals-mem-list ! \ the current (outer-level) definition
137:
138: : free-list ( addr -- )
139: \ free all members of a linked list (link field is first)
140: begin
141: dup while
142: dup @ swap free throw
143: repeat
144: drop ;
145:
146: : prepend-list ( addr1 addr2 -- )
147: \ addr1 is the address of a list element, addr2 is the address of
148: \ the cell containing the address of the first list element
149: 2dup @ swap ! \ store link to next element
150: ! ; \ store pointer to new first element
151:
152: : alignlp-w ( n1 -- n2 )
153: \ cell-align size and generate the corresponding code for aligning lp
154: aligned dup adjust-locals-size ;
155:
156: : alignlp-f ( n1 -- n2 )
157: faligned dup adjust-locals-size ;
158:
159: \ a local declaration group (the braces stuff) is compiled by calling
160: \ the appropriate compile-pushlocal for the locals, starting with the
161: \ righmost local; the names are already created earlier, the
162: \ compile-pushlocal just inserts the offsets from the frame base.
163:
164: : compile-pushlocal-w ( a-addr -- ) ( run-time: w -- )
165: \ compiles a push of a local variable, and adjusts locals-size
166: \ stores the offset of the local variable to a-addr
167: locals-size @ alignlp-w cell+ dup locals-size !
168: swap !
169: postpone >l ;
170:
171: \ locals list operations
172:
173: : list-length ( list -- u )
174: 0 swap begin ( u1 list1 )
175: dup while
176: @ swap 1+ swap
177: repeat
178: drop ;
179:
180: : /list ( list1 u -- list2 )
181: \ list2 is list1 with the first u elements removed
182: 0 ?do
183: @
184: loop ;
185:
186: : common-list ( list1 list2 -- list3 )
187: \ list3 is the largest common tail of both lists.
188: over list-length over list-length - dup 0< if
189: negate >r swap r>
190: then ( long short u )
191: rot swap /list begin ( list3 list4 )
192: 2dup u<> while
193: @ swap @
194: repeat
195: drop ;
196:
197: : sub-list? ( list1 list2 -- f )
198: \ true iff list1 is a sublist of list2
199: over list-length over list-length swap - 0 max /list = ;
200:
201: \ : ocommon-list ( list1 list2 -- list3 ) \ gforth-internal
202: \ \ list1 and list2 are lists, where the heads are at higher addresses than
203: \ \ the tail. list3 is the largest sublist of both lists.
204: \ begin
205: \ 2dup u<>
206: \ while
207: \ 2dup u>
208: \ if
209: \ swap
210: \ then
211: \ @
212: \ repeat
213: \ drop ;
214:
215: \ : osub-list? ( list1 list2 -- f ) \ gforth-internal
216: \ \ true iff list1 is a sublist of list2
217: \ begin
218: \ 2dup u<
219: \ while
220: \ @
221: \ repeat
222: \ = ;
223:
224: \ defer common-list
225: \ defer sub-list?
226:
227: \ ' ocommon-list is common-list
228: \ ' osub-list? is sub-list?
229:
230: : list-size ( list -- u ) \ gforth-internal
231: \ size of the locals frame represented by list
232: 0 ( list n )
233: begin
234: over 0<>
235: while
236: over
237: ((name>)) >body @ max
238: swap @ swap ( get next )
239: repeat
240: faligned nip ;
241:
242: : set-locals-size-list ( list -- )
243: dup locals-list !
244: list-size locals-size ! ;
245:
246: : check-begin ( list -- )
247: \ warn if list is not a sublist of locals-list
248: locals-list @ sub-list? 0= if
249: \ !! print current position
250: >stderr ." compiler was overly optimistic about locals at a BEGIN" cr
251: \ !! print assumption and reality
252: then ;
253:
254: : compile-pushlocal-f ( a-addr -- ) ( run-time: f -- )
255: locals-size @ alignlp-f float+ dup locals-size !
256: swap !
257: postpone f>l ;
258:
259: : compile-pushlocal-d ( a-addr -- ) ( run-time: w1 w2 -- )
260: locals-size @ alignlp-w cell+ cell+ dup locals-size !
261: swap !
262: postpone swap postpone >l postpone >l ;
263:
264: : compile-pushlocal-c ( a-addr -- ) ( run-time: w -- )
265: -1 chars compile-lp+!
266: locals-size @ swap !
267: postpone lp@ postpone c! ;
268:
269: 7 cells 32 + constant locals-name-size \ 32-char name + fields + wiggle room
270:
271: : create-local1 ( "name" -- a-addr )
272: create
273: immediate restrict
274: here 0 , ( place for the offset ) ;
275:
276: variable dict-execute-dp \ the special dp for DICT-EXECUTE
277:
278: 0 value dict-execute-ude \ USABLE-DICTIONARY-END during DICT-EXECUTE
279:
280: : dict-execute1 ( ... addr1 addr2 xt -- ... )
281: \ execute xt with HERE set to addr1 and USABLE-DICTIONARY-END set to addr2
282: dict-execute-dp @ dp 2>r
283: dict-execute-ude ['] usable-dictionary-end defer@ 2>r
284: swap to dict-execute-ude
285: ['] dict-execute-ude is usable-dictionary-end
286: swap to dict-execute-dp
287: dict-execute-dp dpp !
288: catch
289: 2r> is usable-dictionary-end to dict-execute-ude
290: 2r> dpp ! dict-execute-dp !
291: throw ;
292:
293: defer dict-execute ( ... addr1 addr2 xt -- ... )
294:
295: :noname ( ... addr1 addr2 xt -- ... )
296: \ first have a dummy routine, for SOME-CLOCAL etc. below
297: nip nip execute ;
298: is dict-execute
299:
300: : create-local ( " name" -- a-addr )
301: \ defines the local "name"; the offset of the local shall be
302: \ stored in a-addr
303: locals-name-size allocate throw
304: dup locals-mem-list prepend-list
305: locals-name-size cell /string over + ['] create-local1 dict-execute ;
306:
307: variable locals-dp \ so here's the special dp for locals.
308:
309: : lp-offset ( n1 -- n2 )
310: \ converts the offset from the frame start to an offset from lp and
311: \ i.e., the address of the local is lp+locals_size-offset
312: locals-size @ swap - ;
313:
314: : lp-offset, ( n -- )
315: \ converts the offset from the frame start to an offset from lp and
316: \ adds it as inline argument to a preceding locals primitive
317: lp-offset , ;
318:
319: vocabulary locals-types \ this contains all the type specifyers, -- and }
320: locals-types definitions
321:
322: : W: ( "name" -- a-addr xt ) \ gforth w-colon
323: create-local
324: \ xt produces the appropriate locals pushing code when executed
325: ['] compile-pushlocal-w
326: does> ( Compilation: -- ) ( Run-time: -- w )
327: \ compiles a local variable access
328: @ lp-offset compile-@local ;
329:
330: : W^ ( "name" -- a-addr xt ) \ gforth w-caret
331: create-local
332: ['] compile-pushlocal-w
333: does> ( Compilation: -- ) ( Run-time: -- w )
334: postpone laddr# @ lp-offset, ;
335:
336: : F: ( "name" -- a-addr xt ) \ gforth f-colon
337: create-local
338: ['] compile-pushlocal-f
339: does> ( Compilation: -- ) ( Run-time: -- w )
340: @ lp-offset compile-f@local ;
341:
342: : F^ ( "name" -- a-addr xt ) \ gforth f-caret
343: create-local
344: ['] compile-pushlocal-f
345: does> ( Compilation: -- ) ( Run-time: -- w )
346: postpone laddr# @ lp-offset, ;
347:
348: : D: ( "name" -- a-addr xt ) \ gforth d-colon
349: create-local
350: ['] compile-pushlocal-d
351: does> ( Compilation: -- ) ( Run-time: -- w )
352: postpone laddr# @ lp-offset, postpone 2@ ;
353:
354: : D^ ( "name" -- a-addr xt ) \ gforth d-caret
355: create-local
356: ['] compile-pushlocal-d
357: does> ( Compilation: -- ) ( Run-time: -- w )
358: postpone laddr# @ lp-offset, ;
359:
360: : C: ( "name" -- a-addr xt ) \ gforth c-colon
361: create-local
362: ['] compile-pushlocal-c
363: does> ( Compilation: -- ) ( Run-time: -- w )
364: postpone laddr# @ lp-offset, postpone c@ ;
365:
366: : C^ ( "name" -- a-addr xt ) \ gforth c-caret
367: create-local
368: ['] compile-pushlocal-c
369: does> ( Compilation: -- ) ( Run-time: -- w )
370: postpone laddr# @ lp-offset, ;
371:
372: \ you may want to make comments in a locals definitions group:
373: ' \ alias \ ( compilation 'ccc<newline>' -- ; run-time -- ) \ core-ext,block-ext backslash
374: \G Comment till the end of the line if @code{BLK} contains 0 (i.e.,
375: \G while not loading a block), parse and discard the remainder of the
376: \G parse area. Otherwise, parse and discard all subsequent characters
377: \G in the parse area corresponding to the current line.
378: immediate
379:
380: ' ( alias ( ( compilation 'ccc<close-paren>' -- ; run-time -- ) \ core,file paren
381: \G Comment, usually till the next @code{)}: parse and discard all
382: \G subsequent characters in the parse area until ")" is
383: \G encountered. During interactive input, an end-of-line also acts as
384: \G a comment terminator. For file input, it does not; if the
385: \G end-of-file is encountered whilst parsing for the ")" delimiter,
386: \G Gforth will generate a warning.
387: immediate
388:
389: forth definitions
390: also locals-types
391:
392: \ these "locals" are used for comparison in TO
393: c: some-clocal 2drop
394: d: some-dlocal 2drop
395: f: some-flocal 2drop
396: w: some-wlocal 2drop
397:
398: ' dict-execute1 is dict-execute \ now the real thing
399:
400: \ the following gymnastics are for declaring locals without type specifier.
401: \ we exploit a feature of our dictionary: every wordlist
402: \ has it's own methods for finding words etc.
403: \ So we create a vocabulary new-locals, that creates a 'w:' local named x
404: \ when it is asked if it contains x.
405:
406: : new-locals-find ( caddr u w -- nfa )
407: \ this is the find method of the new-locals vocabulary
408: \ make a new local with name caddr u; w is ignored
409: \ the returned nfa denotes a word that produces what W: produces
410: \ !! do the whole thing without nextname
411: drop nextname
412: ['] W: >head-noprim ;
413:
414: previous
415:
416: : new-locals-reveal ( -- )
417: true abort" this should not happen: new-locals-reveal" ;
418:
419: create new-locals-map ( -- wordlist-map )
420: ' new-locals-find A,
421: ' new-locals-reveal A,
422: ' drop A, \ rehash method
423: ' drop A,
424:
425: new-locals-map mappedwordlist Constant new-locals-wl
426:
427: \ slowvoc @
428: \ slowvoc on
429: \ vocabulary new-locals
430: \ slowvoc !
431: \ new-locals-map ' new-locals >body wordlist-map A! \ !! use special access words
432:
433: \ and now, finally, the user interface words
434: : { ( -- latestxt wid 0 ) \ gforth open-brace
435: latestxt get-current
436: get-order new-locals-wl swap 1+ set-order
437: also locals definitions locals-types
438: 0 TO locals-wordlist
439: 0 postpone [ ; immediate
440:
441: locals-types definitions
442:
443: : } ( latestxt wid 0 a-addr1 xt1 ... -- ) \ gforth close-brace
444: \ ends locals definitions
445: ]
446: begin
447: dup
448: while
449: execute
450: repeat
451: drop
452: locals-size @ alignlp-f locals-size ! \ the strictest alignment
453: previous previous
454: set-current lastcfa !
455: locals-list 0 wordlist-id - TO locals-wordlist ;
456:
457: : -- ( addr wid 0 ... -- ) \ gforth dash-dash
458: }
459: [char] } parse 2drop ;
460:
461: forth definitions
462:
463: \ A few thoughts on automatic scopes for locals and how they can be
464: \ implemented:
465:
466: \ We have to combine locals with the control structures. My basic idea
467: \ was to start the life of a local at the declaration point. The life
468: \ would end at any control flow join (THEN, BEGIN etc.) where the local
469: \ is lot live on both input flows (note that the local can still live in
470: \ other, later parts of the control flow). This would make a local live
471: \ as long as you expected and sometimes longer (e.g. a local declared in
472: \ a BEGIN..UNTIL loop would still live after the UNTIL).
473:
474: \ The following example illustrates the problems of this approach:
475:
476: \ { z }
477: \ if
478: \ { x }
479: \ begin
480: \ { y }
481: \ [ 1 cs-roll ] then
482: \ ...
483: \ until
484:
485: \ x lives only until the BEGIN, but the compiler does not know this
486: \ until it compiles the UNTIL (it can deduce it at the THEN, because at
487: \ that point x lives in no thread, but that does not help much). This is
488: \ solved by optimistically assuming at the BEGIN that x lives, but
489: \ warning at the UNTIL that it does not. The user is then responsible
490: \ for checking that x is only used where it lives.
491:
492: \ The produced code might look like this (leaving out alignment code):
493:
494: \ >l ( z )
495: \ ?branch <then>
496: \ >l ( x )
497: \ <begin>:
498: \ >l ( y )
499: \ lp+!# 8 ( RIP: x,y )
500: \ <then>:
501: \ ...
502: \ lp+!# -4 ( adjust lp to <begin> state )
503: \ ?branch <begin>
504: \ lp+!# 4 ( undo adjust )
505:
506: \ The BEGIN problem also has another incarnation:
507:
508: \ AHEAD
509: \ BEGIN
510: \ x
511: \ [ 1 CS-ROLL ] THEN
512: \ { x }
513: \ ...
514: \ UNTIL
515:
516: \ should be legal: The BEGIN is not a control flow join in this case,
517: \ since it cannot be entered from the top; therefore the definition of x
518: \ dominates the use. But the compiler processes the use first, and since
519: \ it does not look ahead to notice the definition, it will complain
520: \ about it. Here's another variation of this problem:
521:
522: \ IF
523: \ { x }
524: \ ELSE
525: \ ...
526: \ AHEAD
527: \ BEGIN
528: \ x
529: \ [ 2 CS-ROLL ] THEN
530: \ ...
531: \ UNTIL
532:
533: \ In this case x is defined before the use, and the definition dominates
534: \ the use, but the compiler does not know this until it processes the
535: \ UNTIL. So what should the compiler assume does live at the BEGIN, if
536: \ the BEGIN is not a control flow join? The safest assumption would be
537: \ the intersection of all locals lists on the control flow
538: \ stack. However, our compiler assumes that the same variables are live
539: \ as on the top of the control flow stack. This covers the following case:
540:
541: \ { x }
542: \ AHEAD
543: \ BEGIN
544: \ x
545: \ [ 1 CS-ROLL ] THEN
546: \ ...
547: \ UNTIL
548:
549: \ If this assumption is too optimistic, the compiler will warn the user.
550:
551: \ Implementation:
552:
553: \ explicit scoping
554:
555: : scope ( compilation -- scope ; run-time -- ) \ gforth
556: cs-push-part scopestart ; immediate
557:
558: : adjust-locals-list ( wid -- )
559: locals-list @ common-list
560: dup list-size adjust-locals-size
561: locals-list ! ;
562:
563: : endscope ( compilation scope -- ; run-time -- ) \ gforth
564: scope?
565: drop adjust-locals-list ; immediate
566:
567: \ adapt the hooks
568:
569: : locals-:-hook ( sys -- sys addr xt n )
570: \ addr is the nfa of the defined word, xt its xt
571: DEFERS :-hook
572: latest latestxt
573: clear-leave-stack
574: 0 locals-size !
575: locals-mem-list @ free-list
576: 0 locals-mem-list !
577: 0 locals-list !
578: dead-code off
579: defstart ;
580:
581: : locals-;-hook ( sys addr xt sys -- sys )
582: def?
583: 0 TO locals-wordlist
584: 0 adjust-locals-size ( not every def ends with an exit )
585: lastcfa ! last !
586: DEFERS ;-hook ;
587:
588: \ THEN (another control flow from before joins the current one):
589: \ The new locals-list is the intersection of the current locals-list and
590: \ the orig-local-list. The new locals-size is the (alignment-adjusted)
591: \ size of the new locals-list. The following code is generated:
592: \ lp+!# (current-locals-size - orig-locals-size)
593: \ <then>:
594: \ lp+!# (orig-locals-size - new-locals-size)
595:
596: \ Of course "lp+!# 0" is not generated. Still this is admittedly a bit
597: \ inefficient, e.g. if there is a locals declaration between IF and
598: \ ELSE. However, if ELSE generates an appropriate "lp+!#" before the
599: \ branch, there will be none after the target <then>.
600:
601: : (then-like) ( orig -- )
602: dead-orig =
603: if
604: >resolve drop
605: else
606: dead-code @
607: if
608: >resolve set-locals-size-list dead-code off
609: else \ both live
610: over list-size adjust-locals-size
611: >resolve
612: adjust-locals-list
613: then
614: then ;
615:
616: : (begin-like) ( -- )
617: dead-code @ if
618: \ set up an assumption of the locals visible here. if the
619: \ users want something to be visible, they have to declare
620: \ that using ASSUME-LIVE
621: backedge-locals @ set-locals-size-list
622: then
623: dead-code off ;
624:
625: \ AGAIN (the current control flow joins another, earlier one):
626: \ If the dest-locals-list is not a subset of the current locals-list,
627: \ issue a warning (see below). The following code is generated:
628: \ lp+!# (current-local-size - dest-locals-size)
629: \ branch <begin>
630:
631: : (again-like) ( dest -- addr )
632: over list-size adjust-locals-size
633: swap check-begin POSTPONE unreachable ;
634:
635: \ UNTIL (the current control flow may join an earlier one or continue):
636: \ Similar to AGAIN. The new locals-list and locals-size are the current
637: \ ones. The following code is generated:
638: \ ?branch-lp+!# <begin> (current-local-size - dest-locals-size)
639:
640: : (until-like) ( list addr xt1 xt2 -- )
641: \ list and addr are a fragment of a cs-item
642: \ xt1 is the conditional branch without lp adjustment, xt2 is with
643: >r >r
644: locals-size @ 2 pick list-size - dup if ( list dest-addr adjustment )
645: r> drop r> compile,
646: swap <resolve ( list adjustment ) ,
647: else ( list dest-addr adjustment )
648: drop
649: r> compile, <resolve
650: r> drop
651: then ( list )
652: check-begin ;
653:
654: : (exit-like) ( -- )
655: 0 adjust-locals-size ;
656:
657: ' locals-:-hook IS :-hook
658: ' locals-;-hook IS ;-hook
659:
660: ' (then-like) IS then-like
661: ' (begin-like) IS begin-like
662: ' (again-like) IS again-like
663: ' (until-like) IS until-like
664: ' (exit-like) IS exit-like
665:
666: \ The words in the locals dictionary space are not deleted until the end
667: \ of the current word. This is a bit too conservative, but very simple.
668:
669: \ There are a few cases to consider: (see above)
670:
671: \ after AGAIN, AHEAD, EXIT (the current control flow is dead):
672: \ We have to special-case the above cases against that. In this case the
673: \ things above are not control flow joins. Everything should be taken
674: \ over from the live flow. No lp+!# is generated.
675:
676: \ About warning against uses of dead locals. There are several options:
677:
678: \ 1) Do not complain (After all, this is Forth;-)
679:
680: \ 2) Additional restrictions can be imposed so that the situation cannot
681: \ arise; the programmer would have to introduce explicit scoping
682: \ declarations in cases like the above one. I.e., complain if there are
683: \ locals that are live before the BEGIN but not before the corresponding
684: \ AGAIN (replace DO etc. for BEGIN and UNTIL etc. for AGAIN).
685:
686: \ 3) The real thing: i.e. complain, iff a local lives at a BEGIN, is
687: \ used on a path starting at the BEGIN, and does not live at the
688: \ corresponding AGAIN. This is somewhat hard to implement. a) How does
689: \ the compiler know when it is working on a path starting at a BEGIN
690: \ (consider "{ x } if begin [ 1 cs-roll ] else x endif again")? b) How
691: \ is the usage info stored?
692:
693: \ For now I'll resort to alternative 2. When it produces warnings they
694: \ will often be spurious, but warnings should be rare. And better
695: \ spurious warnings now and then than days of bug-searching.
696:
697: \ Explicit scoping of locals is implemented by cs-pushing the current
698: \ locals-list and -size (and an unused cell, to make the size equal to
699: \ the other entries) at the start of the scope, and restoring them at
700: \ the end of the scope to the intersection, like THEN does.
701:
702:
703: \ And here's finally the ANS standard stuff
704:
705: : (local) ( addr u -- ) \ local paren-local-paren
706: \ a little space-inefficient, but well deserved ;-)
707: \ In exchange, there are no restrictions whatsoever on using (local)
708: \ as long as you use it in a definition
709: dup
710: if
711: nextname POSTPONE { [ also locals-types ] W: } [ previous ]
712: else
713: 2drop
714: endif ;
715:
716: : >definer ( xt -- definer ) \ gforth
717: \G @var{Definer} is a unique identifier for the way the @var{xt}
718: \G was defined. Words defined with different @code{does>}-codes
719: \G have different definers. The definer can be used for
720: \G comparison and in @code{definer!}.
721: dup >does-code
722: ?dup-if
723: nip 1 or
724: else
725: >code-address
726: then ;
727:
728: : definer! ( definer xt -- ) \ gforth
729: \G The word represented by @var{xt} changes its behaviour to the
730: \G behaviour associated with @var{definer}.
731: over 1 and if
732: swap [ 1 invert ] literal and does-code!
733: else
734: code-address!
735: then ;
736:
737: :noname
738: ' dup >definer [ ' locals-wordlist ] literal >definer =
739: if
740: >body !
741: else
742: -&32 throw
743: endif ;
744: :noname
745: comp' drop dup >definer
746: case
747: [ ' locals-wordlist ] literal >definer \ value
748: OF >body POSTPONE Aliteral POSTPONE ! ENDOF
749: \ !! dependent on c: etc. being does>-defining words
750: \ this works, because >definer uses >does-code in this case,
751: \ which produces a relocatable address
752: [ comp' some-clocal drop ] literal >definer
753: OF POSTPONE laddr# >body @ lp-offset, POSTPONE c! ENDOF
754: [ comp' some-wlocal drop ] literal >definer
755: OF POSTPONE laddr# >body @ lp-offset, POSTPONE ! ENDOF
756: [ comp' some-dlocal drop ] literal >definer
757: OF POSTPONE laddr# >body @ lp-offset, POSTPONE 2! ENDOF
758: [ comp' some-flocal drop ] literal >definer
759: OF POSTPONE laddr# >body @ lp-offset, POSTPONE f! ENDOF
760: -&32 throw
761: endcase ;
762: interpret/compile: TO ( c|w|d|r "name" -- ) \ core-ext,local
763:
764: : locals| ( ... "name ..." -- ) \ local-ext locals-bar
765: \ don't use 'locals|'! use '{'! A portable and free '{'
766: \ implementation is compat/anslocals.fs
767: BEGIN
768: name 2dup s" |" str= 0=
769: WHILE
770: (local)
771: REPEAT
772: drop 0 (local) ; immediate restrict
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