Annotation of gforth/glocals.fs, revision 1.60

1.15      anton       1: \ A powerful locals implementation
                      2: 
1.59      anton       3: \ Copyright (C) 1995,1996,1997,1998,2000,2003,2004,2005,2007 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: 
                    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:
1.44      anton     295: ' \ alias \ ( compilation 'ccc<newline>' -- ; run-time -- ) \ core-ext,block-ext backslash
1.42      anton     296: \G Comment till the end of the line if @code{BLK} contains 0 (i.e.,
                    297: \G while not loading a block), parse and discard the remainder of the
                    298: \G parse area. Otherwise, parse and discard all subsequent characters
                    299: \G in the parse area corresponding to the current line.
                    300: immediate
1.39      crook     301: 
                    302: ' ( alias ( ( compilation 'ccc<close-paren>' -- ; run-time -- ) \ core,file    paren
1.42      anton     303: \G Comment, usually till the next @code{)}: parse and discard all
                    304: \G subsequent characters in the parse area until ")" is
                    305: \G encountered. During interactive input, an end-of-line also acts as
                    306: \G a comment terminator. For file input, it does not; if the
                    307: \G end-of-file is encountered whilst parsing for the ")" delimiter,
                    308: \G Gforth will generate a warning.
1.39      crook     309: immediate
1.1       anton     310: 
                    311: forth definitions
1.54      anton     312: also locals-types
                    313:     
                    314: \ these "locals" are used for comparison in TO
1.1       anton     315: 
1.54      anton     316: c: some-clocal 2drop
                    317: d: some-dlocal 2drop
                    318: f: some-flocal 2drop
                    319: w: some-wlocal 2drop
                    320:     
1.1       anton     321: \ the following gymnastics are for declaring locals without type specifier.
                    322: \ we exploit a feature of our dictionary: every wordlist
                    323: \ has it's own methods for finding words etc.
                    324: \ So we create a vocabulary new-locals, that creates a 'w:' local named x
                    325: \ when it is asked if it contains x.
                    326: 
                    327: : new-locals-find ( caddr u w -- nfa )
                    328: \ this is the find method of the new-locals vocabulary
                    329: \ make a new local with name caddr u; w is ignored
                    330: \ the returned nfa denotes a word that produces what W: produces
                    331: \ !! do the whole thing without nextname
1.3       anton     332:     drop nextname
1.43      anton     333:     ['] W: >head-noprim ;
1.1       anton     334: 
                    335: previous
                    336: 
                    337: : new-locals-reveal ( -- )
                    338:   true abort" this should not happen: new-locals-reveal" ;
                    339: 
1.22      anton     340: create new-locals-map ( -- wordlist-map )
1.29      anton     341: ' new-locals-find A,
                    342: ' new-locals-reveal A,
                    343: ' drop A, \ rehash method
1.34      jwilke    344: ' drop A,
1.1       anton     345: 
1.41      jwilke    346: new-locals-map mappedwordlist Constant new-locals-wl
                    347: 
                    348: \ slowvoc @
                    349: \ slowvoc on
                    350: \ vocabulary new-locals
                    351: \ slowvoc !
                    352: \ new-locals-map ' new-locals >body wordlist-map A! \ !! use special access words
1.1       anton     353: 
                    354: variable old-dpp
                    355: 
                    356: \ and now, finally, the user interface words
1.53      anton     357: : { ( -- latestxt wid 0 ) \ gforth open-brace
1.1       anton     358:     dp old-dpp !
                    359:     locals-dp dpp !
1.53      anton     360:     latestxt get-current
1.41      jwilke    361:     get-order new-locals-wl swap 1+ set-order
1.32      anton     362:     also locals definitions locals-types
1.1       anton     363:     0 TO locals-wordlist
                    364:     0 postpone [ ; immediate
                    365: 
                    366: locals-types definitions
                    367: 
1.53      anton     368: : } ( latestxt wid 0 a-addr1 xt1 ... -- ) \ gforth close-brace
1.1       anton     369:     \ ends locals definitions
                    370:     ] old-dpp @ dpp !
                    371:     begin
                    372:        dup
                    373:     while
                    374:        execute
                    375:     repeat
                    376:     drop
                    377:     locals-size @ alignlp-f locals-size ! \ the strictest alignment
                    378:     previous previous
1.32      anton     379:     set-current lastcfa !
1.37      pazsan    380:     locals-list 0 wordlist-id - TO locals-wordlist ;
1.1       anton     381: 
1.14      anton     382: : -- ( addr wid 0 ... -- ) \ gforth dash-dash
1.1       anton     383:     }
1.9       anton     384:     [char] } parse 2drop ;
1.1       anton     385: 
                    386: forth definitions
                    387: 
                    388: \ A few thoughts on automatic scopes for locals and how they can be
                    389: \ implemented:
                    390: 
                    391: \ We have to combine locals with the control structures. My basic idea
                    392: \ was to start the life of a local at the declaration point. The life
                    393: \ would end at any control flow join (THEN, BEGIN etc.) where the local
                    394: \ is lot live on both input flows (note that the local can still live in
                    395: \ other, later parts of the control flow). This would make a local live
                    396: \ as long as you expected and sometimes longer (e.g. a local declared in
                    397: \ a BEGIN..UNTIL loop would still live after the UNTIL).
                    398: 
                    399: \ The following example illustrates the problems of this approach:
                    400: 
                    401: \ { z }
                    402: \ if
                    403: \   { x }
                    404: \ begin
                    405: \   { y }
                    406: \ [ 1 cs-roll ] then
                    407: \   ...
                    408: \ until
                    409: 
                    410: \ x lives only until the BEGIN, but the compiler does not know this
                    411: \ until it compiles the UNTIL (it can deduce it at the THEN, because at
                    412: \ that point x lives in no thread, but that does not help much). This is
                    413: \ solved by optimistically assuming at the BEGIN that x lives, but
                    414: \ warning at the UNTIL that it does not. The user is then responsible
                    415: \ for checking that x is only used where it lives.
                    416: 
                    417: \ The produced code might look like this (leaving out alignment code):
                    418: 
                    419: \ >l ( z )
                    420: \ ?branch <then>
                    421: \ >l ( x )
                    422: \ <begin>:
                    423: \ >l ( y )
                    424: \ lp+!# 8 ( RIP: x,y )
                    425: \ <then>:
                    426: \ ...
                    427: \ lp+!# -4 ( adjust lp to <begin> state )
                    428: \ ?branch <begin>
                    429: \ lp+!# 4 ( undo adjust )
                    430: 
                    431: \ The BEGIN problem also has another incarnation:
                    432: 
                    433: \ AHEAD
                    434: \ BEGIN
                    435: \   x
                    436: \ [ 1 CS-ROLL ] THEN
                    437: \   { x }
                    438: \   ...
                    439: \ UNTIL
                    440: 
                    441: \ should be legal: The BEGIN is not a control flow join in this case,
                    442: \ since it cannot be entered from the top; therefore the definition of x
                    443: \ dominates the use. But the compiler processes the use first, and since
                    444: \ it does not look ahead to notice the definition, it will complain
                    445: \ about it. Here's another variation of this problem:
                    446: 
                    447: \ IF
                    448: \   { x }
                    449: \ ELSE
                    450: \   ...
                    451: \ AHEAD
                    452: \ BEGIN
                    453: \   x
                    454: \ [ 2 CS-ROLL ] THEN
                    455: \   ...
                    456: \ UNTIL
                    457: 
                    458: \ In this case x is defined before the use, and the definition dominates
                    459: \ the use, but the compiler does not know this until it processes the
                    460: \ UNTIL. So what should the compiler assume does live at the BEGIN, if
                    461: \ the BEGIN is not a control flow join? The safest assumption would be
                    462: \ the intersection of all locals lists on the control flow
                    463: \ stack. However, our compiler assumes that the same variables are live
                    464: \ as on the top of the control flow stack. This covers the following case:
                    465: 
                    466: \ { x }
                    467: \ AHEAD
                    468: \ BEGIN
                    469: \   x
                    470: \ [ 1 CS-ROLL ] THEN
                    471: \   ...
                    472: \ UNTIL
                    473: 
                    474: \ If this assumption is too optimistic, the compiler will warn the user.
                    475: 
1.28      anton     476: \ Implementation:
1.1       anton     477: 
1.3       anton     478: \ explicit scoping
1.1       anton     479: 
1.14      anton     480: : scope ( compilation  -- scope ; run-time  -- ) \ gforth
1.36      pazsan    481:     cs-push-part scopestart ; immediate
                    482: 
                    483: : adjust-locals-list ( wid -- )
1.37      pazsan    484:     locals-list @ common-list
1.36      pazsan    485:     dup list-size adjust-locals-size
1.37      pazsan    486:     locals-list ! ;
1.3       anton     487: 
1.14      anton     488: : endscope ( compilation scope -- ; run-time  -- ) \ gforth
1.36      pazsan    489:     scope?
                    490:     drop  adjust-locals-list ; immediate
1.1       anton     491: 
1.3       anton     492: \ adapt the hooks
1.1       anton     493: 
1.3       anton     494: : locals-:-hook ( sys -- sys addr xt n )
                    495:     \ addr is the nfa of the defined word, xt its xt
1.1       anton     496:     DEFERS :-hook
1.53      anton     497:     latest latestxt
1.1       anton     498:     clear-leave-stack
                    499:     0 locals-size !
                    500:     locals-buffer locals-dp !
1.37      pazsan    501:     0 locals-list !
1.3       anton     502:     dead-code off
                    503:     defstart ;
1.1       anton     504: 
1.3       anton     505: : locals-;-hook ( sys addr xt sys -- sys )
                    506:     def?
1.1       anton     507:     0 TO locals-wordlist
1.3       anton     508:     0 adjust-locals-size ( not every def ends with an exit )
1.1       anton     509:     lastcfa ! last !
                    510:     DEFERS ;-hook ;
                    511: 
1.28      anton     512: \ THEN (another control flow from before joins the current one):
                    513: \ The new locals-list is the intersection of the current locals-list and
                    514: \ the orig-local-list. The new locals-size is the (alignment-adjusted)
                    515: \ size of the new locals-list. The following code is generated:
                    516: \ lp+!# (current-locals-size - orig-locals-size)
                    517: \ <then>:
                    518: \ lp+!# (orig-locals-size - new-locals-size)
                    519: 
                    520: \ Of course "lp+!# 0" is not generated. Still this is admittedly a bit
                    521: \ inefficient, e.g. if there is a locals declaration between IF and
                    522: \ ELSE. However, if ELSE generates an appropriate "lp+!#" before the
                    523: \ branch, there will be none after the target <then>.
                    524: 
1.30      anton     525: : (then-like) ( orig -- )
                    526:     dead-orig =
1.27      pazsan    527:     if
1.30      anton     528:        >resolve drop
1.27      pazsan    529:     else
                    530:         dead-code @
                    531:         if
1.30      anton     532:            >resolve set-locals-size-list dead-code off
1.27      pazsan    533:        else \ both live
1.30      anton     534:            over list-size adjust-locals-size
                    535:            >resolve
1.36      pazsan    536:            adjust-locals-list
1.27      pazsan    537:        then
                    538:     then ;
                    539: 
                    540: : (begin-like) ( -- )
                    541:     dead-code @ if
                    542:        \ set up an assumption of the locals visible here.  if the
                    543:        \ users want something to be visible, they have to declare
                    544:        \ that using ASSUME-LIVE
                    545:        backedge-locals @ set-locals-size-list
                    546:     then
                    547:     dead-code off ;
                    548: 
                    549: \ AGAIN (the current control flow joins another, earlier one):
                    550: \ If the dest-locals-list is not a subset of the current locals-list,
                    551: \ issue a warning (see below). The following code is generated:
                    552: \ lp+!# (current-local-size - dest-locals-size)
                    553: \ branch <begin>
                    554: 
                    555: : (again-like) ( dest -- addr )
                    556:     over list-size adjust-locals-size
                    557:     swap check-begin  POSTPONE unreachable ;
                    558: 
                    559: \ UNTIL (the current control flow may join an earlier one or continue):
                    560: \ Similar to AGAIN. The new locals-list and locals-size are the current
                    561: \ ones. The following code is generated:
                    562: \ ?branch-lp+!# <begin> (current-local-size - dest-locals-size)
                    563: 
                    564: : (until-like) ( list addr xt1 xt2 -- )
                    565:     \ list and addr are a fragment of a cs-item
                    566:     \ xt1 is the conditional branch without lp adjustment, xt2 is with
                    567:     >r >r
                    568:     locals-size @ 2 pick list-size - dup if ( list dest-addr adjustment )
                    569:        r> drop r> compile,
                    570:        swap <resolve ( list adjustment ) ,
                    571:     else ( list dest-addr adjustment )
                    572:        drop
                    573:        r> compile, <resolve
                    574:        r> drop
                    575:     then ( list )
                    576:     check-begin ;
                    577: 
                    578: : (exit-like) ( -- )
                    579:     0 adjust-locals-size ;
                    580: 
1.1       anton     581: ' locals-:-hook IS :-hook
                    582: ' locals-;-hook IS ;-hook
1.27      pazsan    583: 
                    584: ' (then-like)  IS then-like
                    585: ' (begin-like) IS begin-like
                    586: ' (again-like) IS again-like
                    587: ' (until-like) IS until-like
                    588: ' (exit-like)  IS exit-like
1.1       anton     589: 
                    590: \ The words in the locals dictionary space are not deleted until the end
                    591: \ of the current word. This is a bit too conservative, but very simple.
                    592: 
                    593: \ There are a few cases to consider: (see above)
                    594: 
                    595: \ after AGAIN, AHEAD, EXIT (the current control flow is dead):
                    596: \ We have to special-case the above cases against that. In this case the
                    597: \ things above are not control flow joins. Everything should be taken
                    598: \ over from the live flow. No lp+!# is generated.
                    599: 
                    600: \ About warning against uses of dead locals. There are several options:
                    601: 
                    602: \ 1) Do not complain (After all, this is Forth;-)
                    603: 
                    604: \ 2) Additional restrictions can be imposed so that the situation cannot
                    605: \ arise; the programmer would have to introduce explicit scoping
                    606: \ declarations in cases like the above one. I.e., complain if there are
                    607: \ locals that are live before the BEGIN but not before the corresponding
                    608: \ AGAIN (replace DO etc. for BEGIN and UNTIL etc. for AGAIN).
                    609: 
                    610: \ 3) The real thing: i.e. complain, iff a local lives at a BEGIN, is
                    611: \ used on a path starting at the BEGIN, and does not live at the
                    612: \ corresponding AGAIN. This is somewhat hard to implement. a) How does
                    613: \ the compiler know when it is working on a path starting at a BEGIN
                    614: \ (consider "{ x } if begin [ 1 cs-roll ] else x endif again")? b) How
                    615: \ is the usage info stored?
                    616: 
                    617: \ For now I'll resort to alternative 2. When it produces warnings they
                    618: \ will often be spurious, but warnings should be rare. And better
                    619: \ spurious warnings now and then than days of bug-searching.
                    620: 
                    621: \ Explicit scoping of locals is implemented by cs-pushing the current
                    622: \ locals-list and -size (and an unused cell, to make the size equal to
                    623: \ the other entries) at the start of the scope, and restoring them at
                    624: \ the end of the scope to the intersection, like THEN does.
                    625: 
                    626: 
                    627: \ And here's finally the ANS standard stuff
                    628: 
1.14      anton     629: : (local) ( addr u -- ) \ local paren-local-paren
1.3       anton     630:     \ a little space-inefficient, but well deserved ;-)
                    631:     \ In exchange, there are no restrictions whatsoever on using (local)
1.4       anton     632:     \ as long as you use it in a definition
1.3       anton     633:     dup
                    634:     if
                    635:        nextname POSTPONE { [ also locals-types ] W: } [ previous ]
                    636:     else
                    637:        2drop
                    638:     endif ;
1.1       anton     639: 
1.56      anton     640: : >definer ( xt -- definer ) \ gforth
1.48      anton     641:     \G @var{Definer} is a unique identifier for the way the @var{xt}
                    642:     \G was defined.  Words defined with different @code{does>}-codes
                    643:     \G have different definers.  The definer can be used for
                    644:     \G comparison and in @code{definer!}.
1.30      anton     645:     dup >does-code
                    646:     ?dup-if
                    647:        nip 1 or
1.4       anton     648:     else
                    649:        >code-address
                    650:     then ;
                    651: 
1.56      anton     652: : definer! ( definer xt -- ) \ gforth
1.48      anton     653:     \G The word represented by @var{xt} changes its behaviour to the
                    654:     \G behaviour associated with @var{definer}.
1.4       anton     655:     over 1 and if
1.13      anton     656:        swap [ 1 invert ] literal and does-code!
1.4       anton     657:     else
                    658:        code-address!
                    659:     then ;
                    660: 
1.23      pazsan    661: :noname
1.31      anton     662:     ' dup >definer [ ' locals-wordlist ] literal >definer =
1.23      pazsan    663:     if
                    664:        >body !
                    665:     else
                    666:        -&32 throw
                    667:     endif ;
                    668: :noname
1.28      anton     669:     comp' drop dup >definer
1.21      anton     670:     case
1.30      anton     671:        [ ' locals-wordlist ] literal >definer \ value
1.21      anton     672:        OF >body POSTPONE Aliteral POSTPONE ! ENDOF
1.35      anton     673:        \ !! dependent on c: etc. being does>-defining words
                    674:        \ this works, because >definer uses >does-code in this case,
                    675:        \ which produces a relocatable address
1.54      anton     676:        [ comp' some-clocal drop ] literal >definer
1.21      anton     677:        OF POSTPONE laddr# >body @ lp-offset, POSTPONE c! ENDOF
1.54      anton     678:        [ comp' some-wlocal drop ] literal >definer
1.21      anton     679:        OF POSTPONE laddr# >body @ lp-offset, POSTPONE ! ENDOF
1.54      anton     680:        [ comp' some-dlocal drop ] literal >definer
1.21      anton     681:        OF POSTPONE laddr# >body @ lp-offset, POSTPONE 2! ENDOF
1.54      anton     682:        [ comp' some-flocal drop ] literal >definer
1.21      anton     683:        OF POSTPONE laddr# >body @ lp-offset, POSTPONE f! ENDOF
                    684:        -&32 throw
1.23      pazsan    685:     endcase ;
1.24      anton     686: interpret/compile: TO ( c|w|d|r "name" -- ) \ core-ext,local
1.1       anton     687: 
1.58      anton     688: : locals| ( ... "name ..." -- ) \ local-ext locals-bar
1.14      anton     689:     \ don't use 'locals|'! use '{'! A portable and free '{'
1.21      anton     690:     \ implementation is compat/anslocals.fs
1.8       anton     691:     BEGIN
1.49      anton     692:        name 2dup s" |" str= 0=
1.8       anton     693:     WHILE
                    694:        (local)
                    695:     REPEAT
1.14      anton     696:     drop 0 (local) ; immediate restrict

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