Annotation of gforth/glocals.fs, revision 1.58

1.15      anton       1: \ A powerful locals implementation
                      2: 
1.57      anton       3: \ Copyright (C) 1995,1996,1997,1998,2000,2003,2004,2005 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
1.46      anton      19: \ Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111, USA.
1.15      anton      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
1.47      jwilke     90: require extend.fs \ for case
1.1       anton      91: 
1.14      anton      92: : compile-@local ( n -- ) \ gforth compile-fetch-local
1.3       anton      93:  case
1.7       pazsan     94:     0       of postpone @local0 endof
                     95:     1 cells of postpone @local1 endof
                     96:     2 cells of postpone @local2 endof
                     97:     3 cells of postpone @local3 endof
1.3       anton      98:    ( otherwise ) dup postpone @local# ,
                     99:  endcase ;
                    100: 
1.14      anton     101: : compile-f@local ( n -- ) \ gforth compile-f-fetch-local
1.3       anton     102:  case
1.7       pazsan    103:     0        of postpone f@local0 endof
                    104:     1 floats of postpone f@local1 endof
1.3       anton     105:    ( otherwise ) dup postpone f@local# ,
                    106:  endcase ;
                    107: 
1.27      pazsan    108: \ locals stuff needed for control structures
                    109: 
                    110: : compile-lp+! ( n -- ) \ gforth       compile-l-p-plus-store
                    111:     dup negate locals-size +!
                    112:     0 over = if
                    113:     else -1 cells  over = if postpone lp-
                    114:     else  1 floats over = if postpone lp+
                    115:     else  2 floats over = if postpone lp+2
                    116:     else postpone lp+!# dup ,
                    117:     then then then then drop ;
                    118: 
                    119: : adjust-locals-size ( n -- ) \ gforth
                    120:     \ sets locals-size to n and generates an appropriate lp+!
                    121:     locals-size @ swap - compile-lp+! ;
                    122: 
1.1       anton     123: \ the locals stack grows downwards (see primitives)
                    124: \ of the local variables of a group (in braces) the leftmost is on top,
                    125: \ i.e. by going onto the locals stack the order is reversed.
                    126: \ there are alignment gaps if necessary.
                    127: \ lp must have the strictest alignment (usually float) across calls;
                    128: \ for simplicity we align it strictly for every group.
                    129: 
1.5       anton     130: slowvoc @
                    131: slowvoc on \ we want a linked list for the vocabulary locals
1.1       anton     132: vocabulary locals \ this contains the local variables
1.37      pazsan    133: ' locals >body wordlist-id ' locals-list >body !
1.5       anton     134: slowvoc !
1.1       anton     135: 
                    136: create locals-buffer 1000 allot \ !! limited and unsafe
                    137:     \ here the names of the local variables are stored
                    138:     \ we would have problems storing them at the normal dp
                    139: 
                    140: variable locals-dp \ so here's the special dp for locals.
                    141: 
                    142: : alignlp-w ( n1 -- n2 )
                    143:     \ cell-align size and generate the corresponding code for aligning lp
1.3       anton     144:     aligned dup adjust-locals-size ;
1.1       anton     145: 
                    146: : alignlp-f ( n1 -- n2 )
1.3       anton     147:     faligned dup adjust-locals-size ;
1.1       anton     148: 
                    149: \ a local declaration group (the braces stuff) is compiled by calling
                    150: \ the appropriate compile-pushlocal for the locals, starting with the
                    151: \ righmost local; the names are already created earlier, the
                    152: \ compile-pushlocal just inserts the offsets from the frame base.
                    153: 
                    154: : compile-pushlocal-w ( a-addr -- ) ( run-time: w -- )
                    155: \ compiles a push of a local variable, and adjusts locals-size
                    156: \ stores the offset of the local variable to a-addr
                    157:     locals-size @ alignlp-w cell+ dup locals-size !
                    158:     swap !
                    159:     postpone >l ;
                    160: 
1.27      pazsan    161: \ locals list operations
                    162: 
                    163: : common-list ( list1 list2 -- list3 ) \ gforth-internal
                    164: \ list1 and list2 are lists, where the heads are at higher addresses than
                    165: \ the tail. list3 is the largest sublist of both lists.
                    166:  begin
                    167:    2dup u<>
                    168:  while
                    169:    2dup u>
                    170:    if
                    171:      swap
                    172:    then
                    173:    @
                    174:  repeat
                    175:  drop ;
                    176: 
                    177: : sub-list? ( list1 list2 -- f ) \ gforth-internal
                    178: \ true iff list1 is a sublist of list2
                    179:  begin
                    180:    2dup u<
                    181:  while
                    182:    @
                    183:  repeat
                    184:  = ;
                    185: 
                    186: : list-size ( list -- u ) \ gforth-internal
1.36      pazsan    187:     \ size of the locals frame represented by list
                    188:     0 ( list n )
                    189:     begin
                    190:        over 0<>
                    191:     while
                    192:        over
                    193:        ((name>)) >body @ max
                    194:        swap @ swap ( get next )
                    195:     repeat
                    196:     faligned nip ;
1.27      pazsan    197: 
                    198: : set-locals-size-list ( list -- )
1.37      pazsan    199:     dup locals-list !
1.36      pazsan    200:     list-size locals-size ! ;
1.27      pazsan    201: 
                    202: : check-begin ( list -- )
                    203: \ warn if list is not a sublist of locals-list
1.37      pazsan    204:  locals-list @ sub-list? 0= if
1.27      pazsan    205:    \ !! print current position
                    206:    ." compiler was overly optimistic about locals at a BEGIN" cr
                    207:    \ !! print assumption and reality
                    208:  then ;
                    209: 
1.1       anton     210: : compile-pushlocal-f ( a-addr -- ) ( run-time: f -- )
                    211:     locals-size @ alignlp-f float+ dup locals-size !
                    212:     swap !
                    213:     postpone f>l ;
                    214: 
                    215: : compile-pushlocal-d ( a-addr -- ) ( run-time: w1 w2 -- )
                    216:     locals-size @ alignlp-w cell+ cell+ dup locals-size !
                    217:     swap !
                    218:     postpone swap postpone >l postpone >l ;
                    219: 
                    220: : compile-pushlocal-c ( a-addr -- ) ( run-time: w -- )
1.3       anton     221:     -1 chars compile-lp+!
1.1       anton     222:     locals-size @ swap !
                    223:     postpone lp@ postpone c! ;
                    224: 
                    225: : create-local ( " name" -- a-addr )
1.9       anton     226:     \ defines the local "name"; the offset of the local shall be
                    227:     \ stored in a-addr
1.1       anton     228:     create
1.12      anton     229:        immediate restrict
1.1       anton     230:        here 0 , ( place for the offset ) ;
                    231: 
1.3       anton     232: : lp-offset ( n1 -- n2 )
                    233: \ converts the offset from the frame start to an offset from lp and
                    234: \ i.e., the address of the local is lp+locals_size-offset
                    235:   locals-size @ swap - ;
                    236: 
1.1       anton     237: : lp-offset, ( n -- )
                    238: \ converts the offset from the frame start to an offset from lp and
                    239: \ adds it as inline argument to a preceding locals primitive
1.3       anton     240:   lp-offset , ;
1.1       anton     241: 
                    242: vocabulary locals-types \ this contains all the type specifyers, -- and }
                    243: locals-types definitions
                    244: 
1.14      anton     245: : W: ( "name" -- a-addr xt ) \ gforth w-colon
                    246:     create-local
1.1       anton     247:        \ xt produces the appropriate locals pushing code when executed
                    248:        ['] compile-pushlocal-w
                    249:     does> ( Compilation: -- ) ( Run-time: -- w )
                    250:         \ compiles a local variable access
1.3       anton     251:        @ lp-offset compile-@local ;
1.1       anton     252: 
1.14      anton     253: : W^ ( "name" -- a-addr xt ) \ gforth w-caret
                    254:     create-local
1.1       anton     255:        ['] compile-pushlocal-w
                    256:     does> ( Compilation: -- ) ( Run-time: -- w )
                    257:        postpone laddr# @ lp-offset, ;
                    258: 
1.14      anton     259: : F: ( "name" -- a-addr xt ) \ gforth f-colon
                    260:     create-local
1.1       anton     261:        ['] compile-pushlocal-f
                    262:     does> ( Compilation: -- ) ( Run-time: -- w )
1.3       anton     263:        @ lp-offset compile-f@local ;
1.1       anton     264: 
1.14      anton     265: : F^ ( "name" -- a-addr xt ) \ gforth f-caret
                    266:     create-local
1.1       anton     267:        ['] compile-pushlocal-f
                    268:     does> ( Compilation: -- ) ( Run-time: -- w )
                    269:        postpone laddr# @ lp-offset, ;
                    270: 
1.14      anton     271: : D: ( "name" -- a-addr xt ) \ gforth d-colon
                    272:     create-local
1.1       anton     273:        ['] compile-pushlocal-d
                    274:     does> ( Compilation: -- ) ( Run-time: -- w )
                    275:        postpone laddr# @ lp-offset, postpone 2@ ;
                    276: 
1.14      anton     277: : D^ ( "name" -- a-addr xt ) \ gforth d-caret
                    278:     create-local
1.1       anton     279:        ['] compile-pushlocal-d
                    280:     does> ( Compilation: -- ) ( Run-time: -- w )
                    281:        postpone laddr# @ lp-offset, ;
                    282: 
1.14      anton     283: : C: ( "name" -- a-addr xt ) \ gforth c-colon
                    284:     create-local
1.1       anton     285:        ['] compile-pushlocal-c
                    286:     does> ( Compilation: -- ) ( Run-time: -- w )
                    287:        postpone laddr# @ lp-offset, postpone c@ ;
                    288: 
1.14      anton     289: : C^ ( "name" -- a-addr xt ) \ gforth c-caret
                    290:     create-local
1.1       anton     291:        ['] compile-pushlocal-c
                    292:     does> ( Compilation: -- ) ( Run-time: -- w )
                    293:        postpone laddr# @ lp-offset, ;
                    294: 
                    295: \ you may want to make comments in a locals definitions group:
1.44      anton     296: ' \ alias \ ( compilation 'ccc<newline>' -- ; run-time -- ) \ core-ext,block-ext backslash
1.42      anton     297: \G Comment till the end of the line if @code{BLK} contains 0 (i.e.,
                    298: \G while not loading a block), parse and discard the remainder of the
                    299: \G parse area. Otherwise, parse and discard all subsequent characters
                    300: \G in the parse area corresponding to the current line.
                    301: immediate
1.39      crook     302: 
                    303: ' ( alias ( ( compilation 'ccc<close-paren>' -- ; run-time -- ) \ core,file    paren
1.42      anton     304: \G Comment, usually till the next @code{)}: parse and discard all
                    305: \G subsequent characters in the parse area until ")" is
                    306: \G encountered. During interactive input, an end-of-line also acts as
                    307: \G a comment terminator. For file input, it does not; if the
                    308: \G end-of-file is encountered whilst parsing for the ")" delimiter,
                    309: \G Gforth will generate a warning.
1.39      crook     310: immediate
1.1       anton     311: 
                    312: forth definitions
1.54      anton     313: also locals-types
                    314:     
                    315: \ these "locals" are used for comparison in TO
1.1       anton     316: 
1.54      anton     317: c: some-clocal 2drop
                    318: d: some-dlocal 2drop
                    319: f: some-flocal 2drop
                    320: w: some-wlocal 2drop
                    321:     
1.1       anton     322: \ the following gymnastics are for declaring locals without type specifier.
                    323: \ we exploit a feature of our dictionary: every wordlist
                    324: \ has it's own methods for finding words etc.
                    325: \ So we create a vocabulary new-locals, that creates a 'w:' local named x
                    326: \ when it is asked if it contains x.
                    327: 
                    328: : new-locals-find ( caddr u w -- nfa )
                    329: \ this is the find method of the new-locals vocabulary
                    330: \ make a new local with name caddr u; w is ignored
                    331: \ the returned nfa denotes a word that produces what W: produces
                    332: \ !! do the whole thing without nextname
1.3       anton     333:     drop nextname
1.43      anton     334:     ['] W: >head-noprim ;
1.1       anton     335: 
                    336: previous
                    337: 
                    338: : new-locals-reveal ( -- )
                    339:   true abort" this should not happen: new-locals-reveal" ;
                    340: 
1.22      anton     341: create new-locals-map ( -- wordlist-map )
1.29      anton     342: ' new-locals-find A,
                    343: ' new-locals-reveal A,
                    344: ' drop A, \ rehash method
1.34      jwilke    345: ' drop A,
1.1       anton     346: 
1.41      jwilke    347: new-locals-map mappedwordlist Constant new-locals-wl
                    348: 
                    349: \ slowvoc @
                    350: \ slowvoc on
                    351: \ vocabulary new-locals
                    352: \ slowvoc !
                    353: \ new-locals-map ' new-locals >body wordlist-map A! \ !! use special access words
1.1       anton     354: 
                    355: variable old-dpp
                    356: 
                    357: \ and now, finally, the user interface words
1.53      anton     358: : { ( -- latestxt wid 0 ) \ gforth open-brace
1.1       anton     359:     dp old-dpp !
                    360:     locals-dp dpp !
1.53      anton     361:     latestxt get-current
1.41      jwilke    362:     get-order new-locals-wl swap 1+ set-order
1.32      anton     363:     also locals definitions locals-types
1.1       anton     364:     0 TO locals-wordlist
                    365:     0 postpone [ ; immediate
                    366: 
                    367: locals-types definitions
                    368: 
1.53      anton     369: : } ( latestxt wid 0 a-addr1 xt1 ... -- ) \ gforth close-brace
1.1       anton     370:     \ ends locals definitions
                    371:     ] old-dpp @ dpp !
                    372:     begin
                    373:        dup
                    374:     while
                    375:        execute
                    376:     repeat
                    377:     drop
                    378:     locals-size @ alignlp-f locals-size ! \ the strictest alignment
                    379:     previous previous
1.32      anton     380:     set-current lastcfa !
1.37      pazsan    381:     locals-list 0 wordlist-id - TO locals-wordlist ;
1.1       anton     382: 
1.14      anton     383: : -- ( addr wid 0 ... -- ) \ gforth dash-dash
1.1       anton     384:     }
1.9       anton     385:     [char] } parse 2drop ;
1.1       anton     386: 
                    387: forth definitions
                    388: 
                    389: \ A few thoughts on automatic scopes for locals and how they can be
                    390: \ implemented:
                    391: 
                    392: \ We have to combine locals with the control structures. My basic idea
                    393: \ was to start the life of a local at the declaration point. The life
                    394: \ would end at any control flow join (THEN, BEGIN etc.) where the local
                    395: \ is lot live on both input flows (note that the local can still live in
                    396: \ other, later parts of the control flow). This would make a local live
                    397: \ as long as you expected and sometimes longer (e.g. a local declared in
                    398: \ a BEGIN..UNTIL loop would still live after the UNTIL).
                    399: 
                    400: \ The following example illustrates the problems of this approach:
                    401: 
                    402: \ { z }
                    403: \ if
                    404: \   { x }
                    405: \ begin
                    406: \   { y }
                    407: \ [ 1 cs-roll ] then
                    408: \   ...
                    409: \ until
                    410: 
                    411: \ x lives only until the BEGIN, but the compiler does not know this
                    412: \ until it compiles the UNTIL (it can deduce it at the THEN, because at
                    413: \ that point x lives in no thread, but that does not help much). This is
                    414: \ solved by optimistically assuming at the BEGIN that x lives, but
                    415: \ warning at the UNTIL that it does not. The user is then responsible
                    416: \ for checking that x is only used where it lives.
                    417: 
                    418: \ The produced code might look like this (leaving out alignment code):
                    419: 
                    420: \ >l ( z )
                    421: \ ?branch <then>
                    422: \ >l ( x )
                    423: \ <begin>:
                    424: \ >l ( y )
                    425: \ lp+!# 8 ( RIP: x,y )
                    426: \ <then>:
                    427: \ ...
                    428: \ lp+!# -4 ( adjust lp to <begin> state )
                    429: \ ?branch <begin>
                    430: \ lp+!# 4 ( undo adjust )
                    431: 
                    432: \ The BEGIN problem also has another incarnation:
                    433: 
                    434: \ AHEAD
                    435: \ BEGIN
                    436: \   x
                    437: \ [ 1 CS-ROLL ] THEN
                    438: \   { x }
                    439: \   ...
                    440: \ UNTIL
                    441: 
                    442: \ should be legal: The BEGIN is not a control flow join in this case,
                    443: \ since it cannot be entered from the top; therefore the definition of x
                    444: \ dominates the use. But the compiler processes the use first, and since
                    445: \ it does not look ahead to notice the definition, it will complain
                    446: \ about it. Here's another variation of this problem:
                    447: 
                    448: \ IF
                    449: \   { x }
                    450: \ ELSE
                    451: \   ...
                    452: \ AHEAD
                    453: \ BEGIN
                    454: \   x
                    455: \ [ 2 CS-ROLL ] THEN
                    456: \   ...
                    457: \ UNTIL
                    458: 
                    459: \ In this case x is defined before the use, and the definition dominates
                    460: \ the use, but the compiler does not know this until it processes the
                    461: \ UNTIL. So what should the compiler assume does live at the BEGIN, if
                    462: \ the BEGIN is not a control flow join? The safest assumption would be
                    463: \ the intersection of all locals lists on the control flow
                    464: \ stack. However, our compiler assumes that the same variables are live
                    465: \ as on the top of the control flow stack. This covers the following case:
                    466: 
                    467: \ { x }
                    468: \ AHEAD
                    469: \ BEGIN
                    470: \   x
                    471: \ [ 1 CS-ROLL ] THEN
                    472: \   ...
                    473: \ UNTIL
                    474: 
                    475: \ If this assumption is too optimistic, the compiler will warn the user.
                    476: 
1.28      anton     477: \ Implementation:
1.1       anton     478: 
1.3       anton     479: \ explicit scoping
1.1       anton     480: 
1.14      anton     481: : scope ( compilation  -- scope ; run-time  -- ) \ gforth
1.36      pazsan    482:     cs-push-part scopestart ; immediate
                    483: 
                    484: : adjust-locals-list ( wid -- )
1.37      pazsan    485:     locals-list @ common-list
1.36      pazsan    486:     dup list-size adjust-locals-size
1.37      pazsan    487:     locals-list ! ;
1.3       anton     488: 
1.14      anton     489: : endscope ( compilation scope -- ; run-time  -- ) \ gforth
1.36      pazsan    490:     scope?
                    491:     drop  adjust-locals-list ; immediate
1.1       anton     492: 
1.3       anton     493: \ adapt the hooks
1.1       anton     494: 
1.3       anton     495: : locals-:-hook ( sys -- sys addr xt n )
                    496:     \ addr is the nfa of the defined word, xt its xt
1.1       anton     497:     DEFERS :-hook
1.53      anton     498:     latest latestxt
1.1       anton     499:     clear-leave-stack
                    500:     0 locals-size !
                    501:     locals-buffer locals-dp !
1.37      pazsan    502:     0 locals-list !
1.3       anton     503:     dead-code off
                    504:     defstart ;
1.1       anton     505: 
1.3       anton     506: : locals-;-hook ( sys addr xt sys -- sys )
                    507:     def?
1.1       anton     508:     0 TO locals-wordlist
1.3       anton     509:     0 adjust-locals-size ( not every def ends with an exit )
1.1       anton     510:     lastcfa ! last !
                    511:     DEFERS ;-hook ;
                    512: 
1.28      anton     513: \ THEN (another control flow from before joins the current one):
                    514: \ The new locals-list is the intersection of the current locals-list and
                    515: \ the orig-local-list. The new locals-size is the (alignment-adjusted)
                    516: \ size of the new locals-list. The following code is generated:
                    517: \ lp+!# (current-locals-size - orig-locals-size)
                    518: \ <then>:
                    519: \ lp+!# (orig-locals-size - new-locals-size)
                    520: 
                    521: \ Of course "lp+!# 0" is not generated. Still this is admittedly a bit
                    522: \ inefficient, e.g. if there is a locals declaration between IF and
                    523: \ ELSE. However, if ELSE generates an appropriate "lp+!#" before the
                    524: \ branch, there will be none after the target <then>.
                    525: 
1.30      anton     526: : (then-like) ( orig -- )
                    527:     dead-orig =
1.27      pazsan    528:     if
1.30      anton     529:        >resolve drop
1.27      pazsan    530:     else
                    531:         dead-code @
                    532:         if
1.30      anton     533:            >resolve set-locals-size-list dead-code off
1.27      pazsan    534:        else \ both live
1.30      anton     535:            over list-size adjust-locals-size
                    536:            >resolve
1.36      pazsan    537:            adjust-locals-list
1.27      pazsan    538:        then
                    539:     then ;
                    540: 
                    541: : (begin-like) ( -- )
                    542:     dead-code @ if
                    543:        \ set up an assumption of the locals visible here.  if the
                    544:        \ users want something to be visible, they have to declare
                    545:        \ that using ASSUME-LIVE
                    546:        backedge-locals @ set-locals-size-list
                    547:     then
                    548:     dead-code off ;
                    549: 
                    550: \ AGAIN (the current control flow joins another, earlier one):
                    551: \ If the dest-locals-list is not a subset of the current locals-list,
                    552: \ issue a warning (see below). The following code is generated:
                    553: \ lp+!# (current-local-size - dest-locals-size)
                    554: \ branch <begin>
                    555: 
                    556: : (again-like) ( dest -- addr )
                    557:     over list-size adjust-locals-size
                    558:     swap check-begin  POSTPONE unreachable ;
                    559: 
                    560: \ UNTIL (the current control flow may join an earlier one or continue):
                    561: \ Similar to AGAIN. The new locals-list and locals-size are the current
                    562: \ ones. The following code is generated:
                    563: \ ?branch-lp+!# <begin> (current-local-size - dest-locals-size)
                    564: 
                    565: : (until-like) ( list addr xt1 xt2 -- )
                    566:     \ list and addr are a fragment of a cs-item
                    567:     \ xt1 is the conditional branch without lp adjustment, xt2 is with
                    568:     >r >r
                    569:     locals-size @ 2 pick list-size - dup if ( list dest-addr adjustment )
                    570:        r> drop r> compile,
                    571:        swap <resolve ( list adjustment ) ,
                    572:     else ( list dest-addr adjustment )
                    573:        drop
                    574:        r> compile, <resolve
                    575:        r> drop
                    576:     then ( list )
                    577:     check-begin ;
                    578: 
                    579: : (exit-like) ( -- )
                    580:     0 adjust-locals-size ;
                    581: 
1.1       anton     582: ' locals-:-hook IS :-hook
                    583: ' locals-;-hook IS ;-hook
1.27      pazsan    584: 
                    585: ' (then-like)  IS then-like
                    586: ' (begin-like) IS begin-like
                    587: ' (again-like) IS again-like
                    588: ' (until-like) IS until-like
                    589: ' (exit-like)  IS exit-like
1.1       anton     590: 
                    591: \ The words in the locals dictionary space are not deleted until the end
                    592: \ of the current word. This is a bit too conservative, but very simple.
                    593: 
                    594: \ There are a few cases to consider: (see above)
                    595: 
                    596: \ after AGAIN, AHEAD, EXIT (the current control flow is dead):
                    597: \ We have to special-case the above cases against that. In this case the
                    598: \ things above are not control flow joins. Everything should be taken
                    599: \ over from the live flow. No lp+!# is generated.
                    600: 
                    601: \ About warning against uses of dead locals. There are several options:
                    602: 
                    603: \ 1) Do not complain (After all, this is Forth;-)
                    604: 
                    605: \ 2) Additional restrictions can be imposed so that the situation cannot
                    606: \ arise; the programmer would have to introduce explicit scoping
                    607: \ declarations in cases like the above one. I.e., complain if there are
                    608: \ locals that are live before the BEGIN but not before the corresponding
                    609: \ AGAIN (replace DO etc. for BEGIN and UNTIL etc. for AGAIN).
                    610: 
                    611: \ 3) The real thing: i.e. complain, iff a local lives at a BEGIN, is
                    612: \ used on a path starting at the BEGIN, and does not live at the
                    613: \ corresponding AGAIN. This is somewhat hard to implement. a) How does
                    614: \ the compiler know when it is working on a path starting at a BEGIN
                    615: \ (consider "{ x } if begin [ 1 cs-roll ] else x endif again")? b) How
                    616: \ is the usage info stored?
                    617: 
                    618: \ For now I'll resort to alternative 2. When it produces warnings they
                    619: \ will often be spurious, but warnings should be rare. And better
                    620: \ spurious warnings now and then than days of bug-searching.
                    621: 
                    622: \ Explicit scoping of locals is implemented by cs-pushing the current
                    623: \ locals-list and -size (and an unused cell, to make the size equal to
                    624: \ the other entries) at the start of the scope, and restoring them at
                    625: \ the end of the scope to the intersection, like THEN does.
                    626: 
                    627: 
                    628: \ And here's finally the ANS standard stuff
                    629: 
1.14      anton     630: : (local) ( addr u -- ) \ local paren-local-paren
1.3       anton     631:     \ a little space-inefficient, but well deserved ;-)
                    632:     \ In exchange, there are no restrictions whatsoever on using (local)
1.4       anton     633:     \ as long as you use it in a definition
1.3       anton     634:     dup
                    635:     if
                    636:        nextname POSTPONE { [ also locals-types ] W: } [ previous ]
                    637:     else
                    638:        2drop
                    639:     endif ;
1.1       anton     640: 
1.56      anton     641: : >definer ( xt -- definer ) \ gforth
1.48      anton     642:     \G @var{Definer} is a unique identifier for the way the @var{xt}
                    643:     \G was defined.  Words defined with different @code{does>}-codes
                    644:     \G have different definers.  The definer can be used for
                    645:     \G comparison and in @code{definer!}.
1.30      anton     646:     dup >does-code
                    647:     ?dup-if
                    648:        nip 1 or
1.4       anton     649:     else
                    650:        >code-address
                    651:     then ;
                    652: 
1.56      anton     653: : definer! ( definer xt -- ) \ gforth
1.48      anton     654:     \G The word represented by @var{xt} changes its behaviour to the
                    655:     \G behaviour associated with @var{definer}.
1.4       anton     656:     over 1 and if
1.13      anton     657:        swap [ 1 invert ] literal and does-code!
1.4       anton     658:     else
                    659:        code-address!
                    660:     then ;
                    661: 
1.23      pazsan    662: :noname
1.31      anton     663:     ' dup >definer [ ' locals-wordlist ] literal >definer =
1.23      pazsan    664:     if
                    665:        >body !
                    666:     else
                    667:        -&32 throw
                    668:     endif ;
                    669: :noname
1.28      anton     670:     comp' drop dup >definer
1.21      anton     671:     case
1.30      anton     672:        [ ' locals-wordlist ] literal >definer \ value
1.21      anton     673:        OF >body POSTPONE Aliteral POSTPONE ! ENDOF
1.35      anton     674:        \ !! dependent on c: etc. being does>-defining words
                    675:        \ this works, because >definer uses >does-code in this case,
                    676:        \ which produces a relocatable address
1.54      anton     677:        [ comp' some-clocal drop ] literal >definer
1.21      anton     678:        OF POSTPONE laddr# >body @ lp-offset, POSTPONE c! ENDOF
1.54      anton     679:        [ comp' some-wlocal drop ] literal >definer
1.21      anton     680:        OF POSTPONE laddr# >body @ lp-offset, POSTPONE ! ENDOF
1.54      anton     681:        [ comp' some-dlocal drop ] literal >definer
1.21      anton     682:        OF POSTPONE laddr# >body @ lp-offset, POSTPONE 2! ENDOF
1.54      anton     683:        [ comp' some-flocal drop ] literal >definer
1.21      anton     684:        OF POSTPONE laddr# >body @ lp-offset, POSTPONE f! ENDOF
                    685:        -&32 throw
1.23      pazsan    686:     endcase ;
1.24      anton     687: interpret/compile: TO ( c|w|d|r "name" -- ) \ core-ext,local
1.1       anton     688: 
1.58    ! anton     689: : locals| ( ... "name ..." -- ) \ local-ext locals-bar
1.14      anton     690:     \ don't use 'locals|'! use '{'! A portable and free '{'
1.21      anton     691:     \ implementation is compat/anslocals.fs
1.8       anton     692:     BEGIN
1.49      anton     693:        name 2dup s" |" str= 0=
1.8       anton     694:     WHILE
                    695:        (local)
                    696:     REPEAT
1.14      anton     697:     drop 0 (local) ; immediate restrict

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