Annotation of gforth/glocals.fs, revision 1.40

1.15      anton       1: \ A powerful locals implementation
                      2: 
1.38      anton       3: \ Copyright (C) 1995,1996,1997,1998 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
                      9: \ as published by the Free Software Foundation; either version 2
                     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, write to the Free Software
                     19: \ Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
                     20: 
                     21: 
1.16      anton      22: \ More documentation can be found in the manual and in
                     23: \ http://www.complang.tuwien.ac.at/papers/ertl94l.ps.gz
                     24: 
1.1       anton      25: \ Local variables are quite important for writing readable programs, but
                     26: \ IMO (anton) they are the worst part of the standard. There they are very
                     27: \ restricted and have an ugly interface.
                     28: 
                     29: \ So, we implement the locals wordset, but do not recommend using
                     30: \ locals-ext (which is a really bad user interface for locals).
                     31: 
                     32: \ We also have a nice and powerful user-interface for locals: locals are
                     33: \ defined with
                     34: 
                     35: \ { local1 local2 ... }
                     36: \ or
                     37: \ { local1 local2 ... -- ... }
                     38: \ (anything after the -- is just a comment)
                     39: 
                     40: \ Every local in this list consists of an optional type specification
                     41: \ and a name. If there is only the name, it stands for a cell-sized
                     42: \ value (i.e., you get the value of the local variable, not it's
                     43: \ address). The following type specifiers stand before the name:
                     44: 
                     45: \ Specifier    Type    Access
                     46: \ W:           Cell    value
                     47: \ W^           Cell    address
                     48: \ D:           Double  value
                     49: \ D^           Double  address
                     50: \ F:           Float   value
                     51: \ F^           Float   address
                     52: \ C:           Char    value
                     53: \ C^           Char    address
                     54: 
                     55: \ The local variables are initialized with values from the appropriate
                     56: \ stack. In contrast to the examples in the standard document our locals
                     57: \ take the arguments in the expected way: The last local gets the top of
                     58: \ stack, the second last gets the second stack item etc. An example:
                     59: 
                     60: \ : CX* { F: Ar  F: Ai  F: Br  F: Bi -- Cr Ci }
                     61: \ \ complex multiplication
                     62: \  Ar Br f* Ai Bi f* f-
                     63: \  Ar Bi f* Ai Br f* f+ ;
                     64: 
                     65: \ There will also be a way to add user types, but it is not yet decided,
                     66: \ how. Ideas are welcome.
                     67: 
                     68: \ Locals defined in this manner live until (!! see below). 
                     69: \ Their names can be used during this time to get
                     70: \ their value or address; The addresses produced in this way become
                     71: \ invalid at the end of the lifetime.
                     72: 
                     73: \ Values can be changed with TO, but this is not recomended (TO is a
                     74: \ kludge and words lose the single-assignment property, which makes them
                     75: \ harder to analyse).
                     76: 
                     77: \ As for the internals, we use a special locals stack. This eliminates
                     78: \ the problems and restrictions of reusing the return stack and allows
                     79: \ to store floats as locals: the return stack is not guaranteed to be
                     80: \ aligned correctly, but our locals stack must be float-aligned between
                     81: \ words.
                     82: 
                     83: \ Other things about the internals are pretty unclear now.
                     84: 
                     85: \ Currently locals may only be
                     86: \ defined at the outer level and TO is not supported.
                     87: 
1.33      anton      88: require search.fs
1.14      anton      89: require float.fs
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: 
                    135: create locals-buffer 1000 allot \ !! limited and unsafe
                    136:     \ here the names of the local variables are stored
                    137:     \ we would have problems storing them at the normal dp
                    138: 
                    139: variable locals-dp \ so here's the special dp for locals.
                    140: 
                    141: : alignlp-w ( n1 -- n2 )
                    142:     \ cell-align size and generate the corresponding code for aligning lp
1.3       anton     143:     aligned dup adjust-locals-size ;
1.1       anton     144: 
                    145: : alignlp-f ( n1 -- n2 )
1.3       anton     146:     faligned dup adjust-locals-size ;
1.1       anton     147: 
                    148: \ a local declaration group (the braces stuff) is compiled by calling
                    149: \ the appropriate compile-pushlocal for the locals, starting with the
                    150: \ righmost local; the names are already created earlier, the
                    151: \ compile-pushlocal just inserts the offsets from the frame base.
                    152: 
                    153: : compile-pushlocal-w ( a-addr -- ) ( run-time: w -- )
                    154: \ compiles a push of a local variable, and adjusts locals-size
                    155: \ stores the offset of the local variable to a-addr
                    156:     locals-size @ alignlp-w cell+ dup locals-size !
                    157:     swap !
                    158:     postpone >l ;
                    159: 
1.27      pazsan    160: \ locals list operations
                    161: 
                    162: : common-list ( list1 list2 -- list3 ) \ gforth-internal
                    163: \ list1 and list2 are lists, where the heads are at higher addresses than
                    164: \ the tail. list3 is the largest sublist of both lists.
                    165:  begin
                    166:    2dup u<>
                    167:  while
                    168:    2dup u>
                    169:    if
                    170:      swap
                    171:    then
                    172:    @
                    173:  repeat
                    174:  drop ;
                    175: 
                    176: : sub-list? ( list1 list2 -- f ) \ gforth-internal
                    177: \ true iff list1 is a sublist of list2
                    178:  begin
                    179:    2dup u<
                    180:  while
                    181:    @
                    182:  repeat
                    183:  = ;
                    184: 
                    185: : list-size ( list -- u ) \ gforth-internal
1.36      pazsan    186:     \ size of the locals frame represented by list
                    187:     0 ( list n )
                    188:     begin
                    189:        over 0<>
                    190:     while
                    191:        over
                    192:        ((name>)) >body @ max
                    193:        swap @ swap ( get next )
                    194:     repeat
                    195:     faligned nip ;
1.27      pazsan    196: 
                    197: : set-locals-size-list ( list -- )
1.37      pazsan    198:     dup locals-list !
1.36      pazsan    199:     list-size locals-size ! ;
1.27      pazsan    200: 
                    201: : check-begin ( list -- )
                    202: \ warn if list is not a sublist of locals-list
1.37      pazsan    203:  locals-list @ sub-list? 0= if
1.27      pazsan    204:    \ !! print current position
                    205:    ." compiler was overly optimistic about locals at a BEGIN" cr
                    206:    \ !! print assumption and reality
                    207:  then ;
                    208: 
1.1       anton     209: : compile-pushlocal-f ( a-addr -- ) ( run-time: f -- )
                    210:     locals-size @ alignlp-f float+ dup locals-size !
                    211:     swap !
                    212:     postpone f>l ;
                    213: 
                    214: : compile-pushlocal-d ( a-addr -- ) ( run-time: w1 w2 -- )
                    215:     locals-size @ alignlp-w cell+ cell+ dup locals-size !
                    216:     swap !
                    217:     postpone swap postpone >l postpone >l ;
                    218: 
                    219: : compile-pushlocal-c ( a-addr -- ) ( run-time: w -- )
1.3       anton     220:     -1 chars compile-lp+!
1.1       anton     221:     locals-size @ swap !
                    222:     postpone lp@ postpone c! ;
                    223: 
                    224: : create-local ( " name" -- a-addr )
1.9       anton     225:     \ defines the local "name"; the offset of the local shall be
                    226:     \ stored in a-addr
1.1       anton     227:     create
1.12      anton     228:        immediate restrict
1.1       anton     229:        here 0 , ( place for the offset ) ;
                    230: 
1.3       anton     231: : lp-offset ( n1 -- n2 )
                    232: \ converts the offset from the frame start to an offset from lp and
                    233: \ i.e., the address of the local is lp+locals_size-offset
                    234:   locals-size @ swap - ;
                    235: 
1.1       anton     236: : lp-offset, ( n -- )
                    237: \ converts the offset from the frame start to an offset from lp and
                    238: \ adds it as inline argument to a preceding locals primitive
1.3       anton     239:   lp-offset , ;
1.1       anton     240: 
                    241: vocabulary locals-types \ this contains all the type specifyers, -- and }
                    242: locals-types definitions
                    243: 
1.14      anton     244: : W: ( "name" -- a-addr xt ) \ gforth w-colon
                    245:     create-local
1.1       anton     246:        \ xt produces the appropriate locals pushing code when executed
                    247:        ['] compile-pushlocal-w
                    248:     does> ( Compilation: -- ) ( Run-time: -- w )
                    249:         \ compiles a local variable access
1.3       anton     250:        @ lp-offset compile-@local ;
1.1       anton     251: 
1.14      anton     252: : W^ ( "name" -- a-addr xt ) \ gforth w-caret
                    253:     create-local
1.1       anton     254:        ['] compile-pushlocal-w
                    255:     does> ( Compilation: -- ) ( Run-time: -- w )
                    256:        postpone laddr# @ lp-offset, ;
                    257: 
1.14      anton     258: : F: ( "name" -- a-addr xt ) \ gforth f-colon
                    259:     create-local
1.1       anton     260:        ['] compile-pushlocal-f
                    261:     does> ( Compilation: -- ) ( Run-time: -- w )
1.3       anton     262:        @ lp-offset compile-f@local ;
1.1       anton     263: 
1.14      anton     264: : F^ ( "name" -- a-addr xt ) \ gforth f-caret
                    265:     create-local
1.1       anton     266:        ['] compile-pushlocal-f
                    267:     does> ( Compilation: -- ) ( Run-time: -- w )
                    268:        postpone laddr# @ lp-offset, ;
                    269: 
1.14      anton     270: : D: ( "name" -- a-addr xt ) \ gforth d-colon
                    271:     create-local
1.1       anton     272:        ['] compile-pushlocal-d
                    273:     does> ( Compilation: -- ) ( Run-time: -- w )
                    274:        postpone laddr# @ lp-offset, postpone 2@ ;
                    275: 
1.14      anton     276: : D^ ( "name" -- a-addr xt ) \ gforth d-caret
                    277:     create-local
1.1       anton     278:        ['] compile-pushlocal-d
                    279:     does> ( Compilation: -- ) ( Run-time: -- w )
                    280:        postpone laddr# @ lp-offset, ;
                    281: 
1.14      anton     282: : C: ( "name" -- a-addr xt ) \ gforth c-colon
                    283:     create-local
1.1       anton     284:        ['] compile-pushlocal-c
                    285:     does> ( Compilation: -- ) ( Run-time: -- w )
                    286:        postpone laddr# @ lp-offset, postpone c@ ;
                    287: 
1.14      anton     288: : C^ ( "name" -- a-addr xt ) \ gforth c-caret
                    289:     create-local
1.1       anton     290:        ['] compile-pushlocal-c
                    291:     does> ( Compilation: -- ) ( Run-time: -- w )
                    292:        postpone laddr# @ lp-offset, ;
                    293: 
                    294: \ you may want to make comments in a locals definitions group:
1.39      crook     295: ' \ alias \ ( -- ) \ core-ext,block-ext backslash
                    296: \G Line comment: if @code{BLK} contains 0, parse and discard the remainder
                    297: \G of the parse area. Otherwise, parse and discard all subsequent characters in the
                    298: \G parse area corresponding to the current line.
                    299: immediate 
                    300: 
                    301: ' ( alias ( ( compilation 'ccc<close-paren>' -- ; run-time -- ) \ core,file    paren
                    302: \G Comment: parse and discard all subsequent characters in the parse
1.40    ! crook     303: \G area until "@code{)}" is encountered. During interactive input, an end-of-line
1.39      crook     304: \G also acts as a comment terminator. For file input, it does not; if the
1.40    ! crook     305: \G end-of-file is encountered whilst parsing for the "@code{)}" delimiter, Gforth
1.39      crook     306: \G will generate a warning.
                    307: immediate
1.1       anton     308: 
                    309: forth definitions
                    310: 
                    311: \ the following gymnastics are for declaring locals without type specifier.
                    312: \ we exploit a feature of our dictionary: every wordlist
                    313: \ has it's own methods for finding words etc.
                    314: \ So we create a vocabulary new-locals, that creates a 'w:' local named x
                    315: \ when it is asked if it contains x.
                    316: 
                    317: also locals-types
                    318: 
                    319: : new-locals-find ( caddr u w -- nfa )
                    320: \ this is the find method of the new-locals vocabulary
                    321: \ make a new local with name caddr u; w is ignored
                    322: \ the returned nfa denotes a word that produces what W: produces
                    323: \ !! do the whole thing without nextname
1.3       anton     324:     drop nextname
                    325:     ['] W: >name ;
1.1       anton     326: 
                    327: previous
                    328: 
                    329: : new-locals-reveal ( -- )
                    330:   true abort" this should not happen: new-locals-reveal" ;
                    331: 
1.22      anton     332: create new-locals-map ( -- wordlist-map )
1.29      anton     333: ' new-locals-find A,
                    334: ' new-locals-reveal A,
                    335: ' drop A, \ rehash method
1.34      jwilke    336: ' drop A,
1.1       anton     337: 
1.27      pazsan    338: slowvoc @
                    339: slowvoc on
1.1       anton     340: vocabulary new-locals
1.27      pazsan    341: slowvoc !
1.36      pazsan    342: new-locals-map ' new-locals >body wordlist-map A! \ !! use special access words
1.1       anton     343: 
                    344: variable old-dpp
                    345: 
                    346: \ and now, finally, the user interface words
1.32      anton     347: : { ( -- lastxt wid 0 ) \ gforth open-brace
1.1       anton     348:     dp old-dpp !
                    349:     locals-dp dpp !
1.32      anton     350:     lastxt get-current
1.1       anton     351:     also new-locals
1.32      anton     352:     also locals definitions locals-types
1.1       anton     353:     0 TO locals-wordlist
                    354:     0 postpone [ ; immediate
                    355: 
                    356: locals-types definitions
                    357: 
1.32      anton     358: : } ( lastxt wid 0 a-addr1 xt1 ... -- ) \ gforth close-brace
1.1       anton     359:     \ ends locals definitions
                    360:     ] old-dpp @ dpp !
                    361:     begin
                    362:        dup
                    363:     while
                    364:        execute
                    365:     repeat
                    366:     drop
                    367:     locals-size @ alignlp-f locals-size ! \ the strictest alignment
                    368:     previous previous
1.32      anton     369:     set-current lastcfa !
1.37      pazsan    370:     locals-list 0 wordlist-id - TO locals-wordlist ;
1.1       anton     371: 
1.14      anton     372: : -- ( addr wid 0 ... -- ) \ gforth dash-dash
1.1       anton     373:     }
1.9       anton     374:     [char] } parse 2drop ;
1.1       anton     375: 
                    376: forth definitions
                    377: 
                    378: \ A few thoughts on automatic scopes for locals and how they can be
                    379: \ implemented:
                    380: 
                    381: \ We have to combine locals with the control structures. My basic idea
                    382: \ was to start the life of a local at the declaration point. The life
                    383: \ would end at any control flow join (THEN, BEGIN etc.) where the local
                    384: \ is lot live on both input flows (note that the local can still live in
                    385: \ other, later parts of the control flow). This would make a local live
                    386: \ as long as you expected and sometimes longer (e.g. a local declared in
                    387: \ a BEGIN..UNTIL loop would still live after the UNTIL).
                    388: 
                    389: \ The following example illustrates the problems of this approach:
                    390: 
                    391: \ { z }
                    392: \ if
                    393: \   { x }
                    394: \ begin
                    395: \   { y }
                    396: \ [ 1 cs-roll ] then
                    397: \   ...
                    398: \ until
                    399: 
                    400: \ x lives only until the BEGIN, but the compiler does not know this
                    401: \ until it compiles the UNTIL (it can deduce it at the THEN, because at
                    402: \ that point x lives in no thread, but that does not help much). This is
                    403: \ solved by optimistically assuming at the BEGIN that x lives, but
                    404: \ warning at the UNTIL that it does not. The user is then responsible
                    405: \ for checking that x is only used where it lives.
                    406: 
                    407: \ The produced code might look like this (leaving out alignment code):
                    408: 
                    409: \ >l ( z )
                    410: \ ?branch <then>
                    411: \ >l ( x )
                    412: \ <begin>:
                    413: \ >l ( y )
                    414: \ lp+!# 8 ( RIP: x,y )
                    415: \ <then>:
                    416: \ ...
                    417: \ lp+!# -4 ( adjust lp to <begin> state )
                    418: \ ?branch <begin>
                    419: \ lp+!# 4 ( undo adjust )
                    420: 
                    421: \ The BEGIN problem also has another incarnation:
                    422: 
                    423: \ AHEAD
                    424: \ BEGIN
                    425: \   x
                    426: \ [ 1 CS-ROLL ] THEN
                    427: \   { x }
                    428: \   ...
                    429: \ UNTIL
                    430: 
                    431: \ should be legal: The BEGIN is not a control flow join in this case,
                    432: \ since it cannot be entered from the top; therefore the definition of x
                    433: \ dominates the use. But the compiler processes the use first, and since
                    434: \ it does not look ahead to notice the definition, it will complain
                    435: \ about it. Here's another variation of this problem:
                    436: 
                    437: \ IF
                    438: \   { x }
                    439: \ ELSE
                    440: \   ...
                    441: \ AHEAD
                    442: \ BEGIN
                    443: \   x
                    444: \ [ 2 CS-ROLL ] THEN
                    445: \   ...
                    446: \ UNTIL
                    447: 
                    448: \ In this case x is defined before the use, and the definition dominates
                    449: \ the use, but the compiler does not know this until it processes the
                    450: \ UNTIL. So what should the compiler assume does live at the BEGIN, if
                    451: \ the BEGIN is not a control flow join? The safest assumption would be
                    452: \ the intersection of all locals lists on the control flow
                    453: \ stack. However, our compiler assumes that the same variables are live
                    454: \ as on the top of the control flow stack. This covers the following case:
                    455: 
                    456: \ { x }
                    457: \ AHEAD
                    458: \ BEGIN
                    459: \   x
                    460: \ [ 1 CS-ROLL ] THEN
                    461: \   ...
                    462: \ UNTIL
                    463: 
                    464: \ If this assumption is too optimistic, the compiler will warn the user.
                    465: 
1.28      anton     466: \ Implementation:
1.1       anton     467: 
1.3       anton     468: \ explicit scoping
1.1       anton     469: 
1.14      anton     470: : scope ( compilation  -- scope ; run-time  -- ) \ gforth
1.36      pazsan    471:     cs-push-part scopestart ; immediate
                    472: 
                    473: : adjust-locals-list ( wid -- )
1.37      pazsan    474:     locals-list @ common-list
1.36      pazsan    475:     dup list-size adjust-locals-size
1.37      pazsan    476:     locals-list ! ;
1.3       anton     477: 
1.14      anton     478: : endscope ( compilation scope -- ; run-time  -- ) \ gforth
1.36      pazsan    479:     scope?
                    480:     drop  adjust-locals-list ; immediate
1.1       anton     481: 
1.3       anton     482: \ adapt the hooks
1.1       anton     483: 
1.3       anton     484: : locals-:-hook ( sys -- sys addr xt n )
                    485:     \ addr is the nfa of the defined word, xt its xt
1.1       anton     486:     DEFERS :-hook
                    487:     last @ lastcfa @
                    488:     clear-leave-stack
                    489:     0 locals-size !
                    490:     locals-buffer locals-dp !
1.37      pazsan    491:     0 locals-list !
1.3       anton     492:     dead-code off
                    493:     defstart ;
1.1       anton     494: 
1.3       anton     495: : locals-;-hook ( sys addr xt sys -- sys )
                    496:     def?
1.1       anton     497:     0 TO locals-wordlist
1.3       anton     498:     0 adjust-locals-size ( not every def ends with an exit )
1.1       anton     499:     lastcfa ! last !
                    500:     DEFERS ;-hook ;
                    501: 
1.28      anton     502: \ THEN (another control flow from before joins the current one):
                    503: \ The new locals-list is the intersection of the current locals-list and
                    504: \ the orig-local-list. The new locals-size is the (alignment-adjusted)
                    505: \ size of the new locals-list. The following code is generated:
                    506: \ lp+!# (current-locals-size - orig-locals-size)
                    507: \ <then>:
                    508: \ lp+!# (orig-locals-size - new-locals-size)
                    509: 
                    510: \ Of course "lp+!# 0" is not generated. Still this is admittedly a bit
                    511: \ inefficient, e.g. if there is a locals declaration between IF and
                    512: \ ELSE. However, if ELSE generates an appropriate "lp+!#" before the
                    513: \ branch, there will be none after the target <then>.
                    514: 
1.30      anton     515: : (then-like) ( orig -- )
                    516:     dead-orig =
1.27      pazsan    517:     if
1.30      anton     518:        >resolve drop
1.27      pazsan    519:     else
                    520:         dead-code @
                    521:         if
1.30      anton     522:            >resolve set-locals-size-list dead-code off
1.27      pazsan    523:        else \ both live
1.30      anton     524:            over list-size adjust-locals-size
                    525:            >resolve
1.36      pazsan    526:            adjust-locals-list
1.27      pazsan    527:        then
                    528:     then ;
                    529: 
                    530: : (begin-like) ( -- )
                    531:     dead-code @ if
                    532:        \ set up an assumption of the locals visible here.  if the
                    533:        \ users want something to be visible, they have to declare
                    534:        \ that using ASSUME-LIVE
                    535:        backedge-locals @ set-locals-size-list
                    536:     then
                    537:     dead-code off ;
                    538: 
                    539: \ AGAIN (the current control flow joins another, earlier one):
                    540: \ If the dest-locals-list is not a subset of the current locals-list,
                    541: \ issue a warning (see below). The following code is generated:
                    542: \ lp+!# (current-local-size - dest-locals-size)
                    543: \ branch <begin>
                    544: 
                    545: : (again-like) ( dest -- addr )
                    546:     over list-size adjust-locals-size
                    547:     swap check-begin  POSTPONE unreachable ;
                    548: 
                    549: \ UNTIL (the current control flow may join an earlier one or continue):
                    550: \ Similar to AGAIN. The new locals-list and locals-size are the current
                    551: \ ones. The following code is generated:
                    552: \ ?branch-lp+!# <begin> (current-local-size - dest-locals-size)
                    553: 
                    554: : (until-like) ( list addr xt1 xt2 -- )
                    555:     \ list and addr are a fragment of a cs-item
                    556:     \ xt1 is the conditional branch without lp adjustment, xt2 is with
                    557:     >r >r
                    558:     locals-size @ 2 pick list-size - dup if ( list dest-addr adjustment )
                    559:        r> drop r> compile,
                    560:        swap <resolve ( list adjustment ) ,
                    561:     else ( list dest-addr adjustment )
                    562:        drop
                    563:        r> compile, <resolve
                    564:        r> drop
                    565:     then ( list )
                    566:     check-begin ;
                    567: 
                    568: : (exit-like) ( -- )
                    569:     0 adjust-locals-size ;
                    570: 
1.1       anton     571: ' locals-:-hook IS :-hook
                    572: ' locals-;-hook IS ;-hook
1.27      pazsan    573: 
                    574: ' (then-like)  IS then-like
                    575: ' (begin-like) IS begin-like
                    576: ' (again-like) IS again-like
                    577: ' (until-like) IS until-like
                    578: ' (exit-like)  IS exit-like
1.1       anton     579: 
                    580: \ The words in the locals dictionary space are not deleted until the end
                    581: \ of the current word. This is a bit too conservative, but very simple.
                    582: 
                    583: \ There are a few cases to consider: (see above)
                    584: 
                    585: \ after AGAIN, AHEAD, EXIT (the current control flow is dead):
                    586: \ We have to special-case the above cases against that. In this case the
                    587: \ things above are not control flow joins. Everything should be taken
                    588: \ over from the live flow. No lp+!# is generated.
                    589: 
                    590: \ About warning against uses of dead locals. There are several options:
                    591: 
                    592: \ 1) Do not complain (After all, this is Forth;-)
                    593: 
                    594: \ 2) Additional restrictions can be imposed so that the situation cannot
                    595: \ arise; the programmer would have to introduce explicit scoping
                    596: \ declarations in cases like the above one. I.e., complain if there are
                    597: \ locals that are live before the BEGIN but not before the corresponding
                    598: \ AGAIN (replace DO etc. for BEGIN and UNTIL etc. for AGAIN).
                    599: 
                    600: \ 3) The real thing: i.e. complain, iff a local lives at a BEGIN, is
                    601: \ used on a path starting at the BEGIN, and does not live at the
                    602: \ corresponding AGAIN. This is somewhat hard to implement. a) How does
                    603: \ the compiler know when it is working on a path starting at a BEGIN
                    604: \ (consider "{ x } if begin [ 1 cs-roll ] else x endif again")? b) How
                    605: \ is the usage info stored?
                    606: 
                    607: \ For now I'll resort to alternative 2. When it produces warnings they
                    608: \ will often be spurious, but warnings should be rare. And better
                    609: \ spurious warnings now and then than days of bug-searching.
                    610: 
                    611: \ Explicit scoping of locals is implemented by cs-pushing the current
                    612: \ locals-list and -size (and an unused cell, to make the size equal to
                    613: \ the other entries) at the start of the scope, and restoring them at
                    614: \ the end of the scope to the intersection, like THEN does.
                    615: 
                    616: 
                    617: \ And here's finally the ANS standard stuff
                    618: 
1.14      anton     619: : (local) ( addr u -- ) \ local paren-local-paren
1.3       anton     620:     \ a little space-inefficient, but well deserved ;-)
                    621:     \ In exchange, there are no restrictions whatsoever on using (local)
1.4       anton     622:     \ as long as you use it in a definition
1.3       anton     623:     dup
                    624:     if
                    625:        nextname POSTPONE { [ also locals-types ] W: } [ previous ]
                    626:     else
                    627:        2drop
                    628:     endif ;
1.1       anton     629: 
1.4       anton     630: : >definer ( xt -- definer )
                    631:     \ this gives a unique identifier for the way the xt was defined
                    632:     \ words defined with different does>-codes have different definers
                    633:     \ the definer can be used for comparison and in definer!
1.30      anton     634:     dup >does-code
                    635:     ?dup-if
                    636:        nip 1 or
1.4       anton     637:     else
                    638:        >code-address
                    639:     then ;
                    640: 
                    641: : definer! ( definer xt -- )
                    642:     \ gives the word represented by xt the behaviour associated with definer
                    643:     over 1 and if
1.13      anton     644:        swap [ 1 invert ] literal and does-code!
1.4       anton     645:     else
                    646:        code-address!
                    647:     then ;
                    648: 
1.23      pazsan    649: :noname
1.31      anton     650:     ' dup >definer [ ' locals-wordlist ] literal >definer =
1.23      pazsan    651:     if
                    652:        >body !
                    653:     else
                    654:        -&32 throw
                    655:     endif ;
                    656: :noname
1.21      anton     657:     0 0 0. 0.0e0 { c: clocal w: wlocal d: dlocal f: flocal }
1.28      anton     658:     comp' drop dup >definer
1.21      anton     659:     case
1.30      anton     660:        [ ' locals-wordlist ] literal >definer \ value
1.21      anton     661:        OF >body POSTPONE Aliteral POSTPONE ! ENDOF
1.35      anton     662:        \ !! dependent on c: etc. being does>-defining words
                    663:        \ this works, because >definer uses >does-code in this case,
                    664:        \ which produces a relocatable address
                    665:        [ comp' clocal drop >definer ] literal
1.21      anton     666:        OF POSTPONE laddr# >body @ lp-offset, POSTPONE c! ENDOF
1.35      anton     667:        [ comp' wlocal drop >definer ] literal
1.21      anton     668:        OF POSTPONE laddr# >body @ lp-offset, POSTPONE ! ENDOF
1.35      anton     669:        [ comp' dlocal drop >definer ] literal
1.21      anton     670:        OF POSTPONE laddr# >body @ lp-offset, POSTPONE 2! ENDOF
1.35      anton     671:        [ comp' flocal drop >definer ] literal
1.21      anton     672:        OF POSTPONE laddr# >body @ lp-offset, POSTPONE f! ENDOF
                    673:        -&32 throw
1.23      pazsan    674:     endcase ;
1.24      anton     675: interpret/compile: TO ( c|w|d|r "name" -- ) \ core-ext,local
1.1       anton     676: 
1.6       pazsan    677: : locals|
1.14      anton     678:     \ don't use 'locals|'! use '{'! A portable and free '{'
1.21      anton     679:     \ implementation is compat/anslocals.fs
1.8       anton     680:     BEGIN
                    681:        name 2dup s" |" compare 0<>
                    682:     WHILE
                    683:        (local)
                    684:     REPEAT
1.14      anton     685:     drop 0 (local) ; immediate restrict

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