File:  [gforth] / gforth / glocals.fs
Revision 1.65: download - view: text, annotated - select for diffs
Tue Feb 7 16:48:55 2012 UTC (9 years, 10 months ago) by anton
Branches: MAIN
CVS tags: HEAD
Bootstrapping bug fix:
  use old version of glocals unless USABLE-DICTIONARY-END is deferred

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

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