Annotation of gforth/glocals.fs, revision 1.66

1.15      anton       1: \ A powerful locals implementation
                      2: 
1.63      anton       3: \ Copyright (C) 1995,1996,1997,1998,2000,2003,2004,2005,2007,2011 Free Software Foundation, Inc.
1.15      anton       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
1.60      anton       9: \ as published by the Free Software Foundation, either version 3
1.15      anton      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
1.60      anton      18: \ along with this program. If not, see http://www.gnu.org/licenses/.
1.15      anton      19: 
                     20: 
1.16      anton      21: \ More documentation can be found in the manual and in
                     22: \ http://www.complang.tuwien.ac.at/papers/ertl94l.ps.gz
                     23: 
1.1       anton      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: 
1.33      anton      87: require search.fs
1.14      anton      88: require float.fs
1.47      jwilke     89: require extend.fs \ for case
1.1       anton      90: 
1.14      anton      91: : compile-@local ( n -- ) \ gforth compile-fetch-local
1.3       anton      92:  case
1.7       pazsan     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
1.3       anton      97:    ( otherwise ) dup postpone @local# ,
                     98:  endcase ;
                     99: 
1.14      anton     100: : compile-f@local ( n -- ) \ gforth compile-f-fetch-local
1.3       anton     101:  case
1.7       pazsan    102:     0        of postpone f@local0 endof
                    103:     1 floats of postpone f@local1 endof
1.3       anton     104:    ( otherwise ) dup postpone f@local# ,
                    105:  endcase ;
                    106: 
1.27      pazsan    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: 
1.1       anton     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: 
1.5       anton     129: slowvoc @
                    130: slowvoc on \ we want a linked list for the vocabulary locals
1.1       anton     131: vocabulary locals \ this contains the local variables
1.37      pazsan    132: ' locals >body wordlist-id ' locals-list >body !
1.5       anton     133: slowvoc !
1.1       anton     134: 
1.62      anton     135: variable locals-mem-list \ linked list of all locals name memory in
                    136: 0 locals-mem-list !      \ the current (outer-level) definition
1.1       anton     137: 
1.62      anton     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
1.1       anton     151: 
                    152: : alignlp-w ( n1 -- n2 )
                    153:     \ cell-align size and generate the corresponding code for aligning lp
1.3       anton     154:     aligned dup adjust-locals-size ;
1.1       anton     155: 
                    156: : alignlp-f ( n1 -- n2 )
1.3       anton     157:     faligned dup adjust-locals-size ;
1.1       anton     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: 
1.27      pazsan    171: \ locals list operations
                    172: 
1.66    ! anton     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?
1.27      pazsan    229: 
                    230: : list-size ( list -- u ) \ gforth-internal
1.36      pazsan    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 ;
1.27      pazsan    241: 
                    242: : set-locals-size-list ( list -- )
1.37      pazsan    243:     dup locals-list !
1.36      pazsan    244:     list-size locals-size ! ;
1.27      pazsan    245: 
                    246: : check-begin ( list -- )
                    247: \ warn if list is not a sublist of locals-list
1.37      pazsan    248:  locals-list @ sub-list? 0= if
1.27      pazsan    249:    \ !! print current position
1.64      pazsan    250:      >stderr ." compiler was overly optimistic about locals at a BEGIN" cr
1.27      pazsan    251:    \ !! print assumption and reality
                    252:  then ;
                    253: 
1.1       anton     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 -- )
1.3       anton     265:     -1 chars compile-lp+!
1.1       anton     266:     locals-size @ swap !
                    267:     postpone lp@ postpone c! ;
                    268: 
1.62      anton     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: 
1.1       anton     300: : create-local ( " name" -- a-addr )
1.9       anton     301:     \ defines the local "name"; the offset of the local shall be
                    302:     \ stored in a-addr
1.62      anton     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.
1.1       anton     308: 
1.3       anton     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: 
1.1       anton     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
1.3       anton     317:   lp-offset , ;
1.1       anton     318: 
                    319: vocabulary locals-types \ this contains all the type specifyers, -- and }
                    320: locals-types definitions
                    321: 
1.14      anton     322: : W: ( "name" -- a-addr xt ) \ gforth w-colon
                    323:     create-local
1.1       anton     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
1.3       anton     328:        @ lp-offset compile-@local ;
1.1       anton     329: 
1.14      anton     330: : W^ ( "name" -- a-addr xt ) \ gforth w-caret
                    331:     create-local
1.1       anton     332:        ['] compile-pushlocal-w
                    333:     does> ( Compilation: -- ) ( Run-time: -- w )
                    334:        postpone laddr# @ lp-offset, ;
                    335: 
1.14      anton     336: : F: ( "name" -- a-addr xt ) \ gforth f-colon
                    337:     create-local
1.1       anton     338:        ['] compile-pushlocal-f
                    339:     does> ( Compilation: -- ) ( Run-time: -- w )
1.3       anton     340:        @ lp-offset compile-f@local ;
1.1       anton     341: 
1.14      anton     342: : F^ ( "name" -- a-addr xt ) \ gforth f-caret
                    343:     create-local
1.1       anton     344:        ['] compile-pushlocal-f
                    345:     does> ( Compilation: -- ) ( Run-time: -- w )
                    346:        postpone laddr# @ lp-offset, ;
                    347: 
1.14      anton     348: : D: ( "name" -- a-addr xt ) \ gforth d-colon
                    349:     create-local
1.1       anton     350:        ['] compile-pushlocal-d
                    351:     does> ( Compilation: -- ) ( Run-time: -- w )
                    352:        postpone laddr# @ lp-offset, postpone 2@ ;
                    353: 
1.14      anton     354: : D^ ( "name" -- a-addr xt ) \ gforth d-caret
                    355:     create-local
1.1       anton     356:        ['] compile-pushlocal-d
                    357:     does> ( Compilation: -- ) ( Run-time: -- w )
                    358:        postpone laddr# @ lp-offset, ;
                    359: 
1.14      anton     360: : C: ( "name" -- a-addr xt ) \ gforth c-colon
                    361:     create-local
1.1       anton     362:        ['] compile-pushlocal-c
                    363:     does> ( Compilation: -- ) ( Run-time: -- w )
                    364:        postpone laddr# @ lp-offset, postpone c@ ;
                    365: 
1.14      anton     366: : C^ ( "name" -- a-addr xt ) \ gforth c-caret
                    367:     create-local
1.1       anton     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:
1.44      anton     373: ' \ alias \ ( compilation 'ccc<newline>' -- ; run-time -- ) \ core-ext,block-ext backslash
1.42      anton     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
1.39      crook     379: 
                    380: ' ( alias ( ( compilation 'ccc<close-paren>' -- ; run-time -- ) \ core,file    paren
1.42      anton     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.
1.39      crook     387: immediate
1.1       anton     388: 
                    389: forth definitions
1.54      anton     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
1.62      anton     397: 
                    398: ' dict-execute1 is dict-execute \ now the real thing
1.54      anton     399:     
1.1       anton     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
1.3       anton     411:     drop nextname
1.43      anton     412:     ['] W: >head-noprim ;
1.1       anton     413: 
                    414: previous
                    415: 
                    416: : new-locals-reveal ( -- )
                    417:   true abort" this should not happen: new-locals-reveal" ;
                    418: 
1.22      anton     419: create new-locals-map ( -- wordlist-map )
1.29      anton     420: ' new-locals-find A,
                    421: ' new-locals-reveal A,
                    422: ' drop A, \ rehash method
1.34      jwilke    423: ' drop A,
1.1       anton     424: 
1.41      jwilke    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
1.1       anton     432: 
                    433: \ and now, finally, the user interface words
1.53      anton     434: : { ( -- latestxt wid 0 ) \ gforth open-brace
                    435:     latestxt get-current
1.41      jwilke    436:     get-order new-locals-wl swap 1+ set-order
1.32      anton     437:     also locals definitions locals-types
1.1       anton     438:     0 TO locals-wordlist
                    439:     0 postpone [ ; immediate
                    440: 
                    441: locals-types definitions
                    442: 
1.53      anton     443: : } ( latestxt wid 0 a-addr1 xt1 ... -- ) \ gforth close-brace
1.1       anton     444:     \ ends locals definitions
1.61      anton     445:     ]
1.1       anton     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
1.32      anton     454:     set-current lastcfa !
1.37      pazsan    455:     locals-list 0 wordlist-id - TO locals-wordlist ;
1.1       anton     456: 
1.14      anton     457: : -- ( addr wid 0 ... -- ) \ gforth dash-dash
1.1       anton     458:     }
1.9       anton     459:     [char] } parse 2drop ;
1.1       anton     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: 
1.28      anton     551: \ Implementation:
1.1       anton     552: 
1.3       anton     553: \ explicit scoping
1.1       anton     554: 
1.14      anton     555: : scope ( compilation  -- scope ; run-time  -- ) \ gforth
1.36      pazsan    556:     cs-push-part scopestart ; immediate
                    557: 
                    558: : adjust-locals-list ( wid -- )
1.37      pazsan    559:     locals-list @ common-list
1.36      pazsan    560:     dup list-size adjust-locals-size
1.37      pazsan    561:     locals-list ! ;
1.3       anton     562: 
1.14      anton     563: : endscope ( compilation scope -- ; run-time  -- ) \ gforth
1.36      pazsan    564:     scope?
                    565:     drop  adjust-locals-list ; immediate
1.1       anton     566: 
1.3       anton     567: \ adapt the hooks
1.1       anton     568: 
1.3       anton     569: : locals-:-hook ( sys -- sys addr xt n )
                    570:     \ addr is the nfa of the defined word, xt its xt
1.1       anton     571:     DEFERS :-hook
1.53      anton     572:     latest latestxt
1.1       anton     573:     clear-leave-stack
                    574:     0 locals-size !
1.62      anton     575:     locals-mem-list @ free-list
                    576:     0 locals-mem-list !
1.37      pazsan    577:     0 locals-list !
1.3       anton     578:     dead-code off
                    579:     defstart ;
1.1       anton     580: 
1.3       anton     581: : locals-;-hook ( sys addr xt sys -- sys )
                    582:     def?
1.1       anton     583:     0 TO locals-wordlist
1.3       anton     584:     0 adjust-locals-size ( not every def ends with an exit )
1.1       anton     585:     lastcfa ! last !
                    586:     DEFERS ;-hook ;
                    587: 
1.28      anton     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: 
1.30      anton     601: : (then-like) ( orig -- )
                    602:     dead-orig =
1.27      pazsan    603:     if
1.30      anton     604:        >resolve drop
1.27      pazsan    605:     else
                    606:         dead-code @
                    607:         if
1.30      anton     608:            >resolve set-locals-size-list dead-code off
1.27      pazsan    609:        else \ both live
1.30      anton     610:            over list-size adjust-locals-size
                    611:            >resolve
1.36      pazsan    612:            adjust-locals-list
1.27      pazsan    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: 
1.1       anton     657: ' locals-:-hook IS :-hook
                    658: ' locals-;-hook IS ;-hook
1.27      pazsan    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
1.1       anton     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: 
1.14      anton     705: : (local) ( addr u -- ) \ local paren-local-paren
1.3       anton     706:     \ a little space-inefficient, but well deserved ;-)
                    707:     \ In exchange, there are no restrictions whatsoever on using (local)
1.4       anton     708:     \ as long as you use it in a definition
1.3       anton     709:     dup
                    710:     if
                    711:        nextname POSTPONE { [ also locals-types ] W: } [ previous ]
                    712:     else
                    713:        2drop
                    714:     endif ;
1.1       anton     715: 
1.56      anton     716: : >definer ( xt -- definer ) \ gforth
1.48      anton     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!}.
1.30      anton     721:     dup >does-code
                    722:     ?dup-if
                    723:        nip 1 or
1.4       anton     724:     else
                    725:        >code-address
                    726:     then ;
                    727: 
1.56      anton     728: : definer! ( definer xt -- ) \ gforth
1.48      anton     729:     \G The word represented by @var{xt} changes its behaviour to the
                    730:     \G behaviour associated with @var{definer}.
1.4       anton     731:     over 1 and if
1.13      anton     732:        swap [ 1 invert ] literal and does-code!
1.4       anton     733:     else
                    734:        code-address!
                    735:     then ;
                    736: 
1.23      pazsan    737: :noname
1.31      anton     738:     ' dup >definer [ ' locals-wordlist ] literal >definer =
1.23      pazsan    739:     if
                    740:        >body !
                    741:     else
                    742:        -&32 throw
                    743:     endif ;
                    744: :noname
1.28      anton     745:     comp' drop dup >definer
1.21      anton     746:     case
1.30      anton     747:        [ ' locals-wordlist ] literal >definer \ value
1.21      anton     748:        OF >body POSTPONE Aliteral POSTPONE ! ENDOF
1.35      anton     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
1.54      anton     752:        [ comp' some-clocal drop ] literal >definer
1.21      anton     753:        OF POSTPONE laddr# >body @ lp-offset, POSTPONE c! ENDOF
1.54      anton     754:        [ comp' some-wlocal drop ] literal >definer
1.21      anton     755:        OF POSTPONE laddr# >body @ lp-offset, POSTPONE ! ENDOF
1.54      anton     756:        [ comp' some-dlocal drop ] literal >definer
1.21      anton     757:        OF POSTPONE laddr# >body @ lp-offset, POSTPONE 2! ENDOF
1.54      anton     758:        [ comp' some-flocal drop ] literal >definer
1.21      anton     759:        OF POSTPONE laddr# >body @ lp-offset, POSTPONE f! ENDOF
                    760:        -&32 throw
1.23      pazsan    761:     endcase ;
1.24      anton     762: interpret/compile: TO ( c|w|d|r "name" -- ) \ core-ext,local
1.1       anton     763: 
1.58      anton     764: : locals| ( ... "name ..." -- ) \ local-ext locals-bar
1.14      anton     765:     \ don't use 'locals|'! use '{'! A portable and free '{'
1.21      anton     766:     \ implementation is compat/anslocals.fs
1.8       anton     767:     BEGIN
1.49      anton     768:        name 2dup s" |" str= 0=
1.8       anton     769:     WHILE
                    770:        (local)
                    771:     REPEAT
1.14      anton     772:     drop 0 (local) ; immediate restrict

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