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    1: \ A powerful locals implementation
    2: 
    3: \ Copyright (C) 1995 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 2
   10: \ of the License, or (at your option) any later version.
   11: 
   12: \ This program is distributed in the hope that it will be useful,
   13: \ but WITHOUT ANY WARRANTY; without even the implied warranty of
   14: \ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   15: \ GNU General Public License for more details.
   16: 
   17: \ You should have received a copy of the GNU General Public License
   18: \ along with this program; if not, write to the Free Software
   19: \ Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
   20: 
   21: 
   22: \ More documentation can be found in the manual and in
   23: \ http://www.complang.tuwien.ac.at/papers/ertl94l.ps.gz
   24: 
   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: 
   88: require search-order.fs
   89: require float.fs
   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: \ the locals stack grows downwards (see primitives)
  108: \ of the local variables of a group (in braces) the leftmost is on top,
  109: \ i.e. by going onto the locals stack the order is reversed.
  110: \ there are alignment gaps if necessary.
  111: \ lp must have the strictest alignment (usually float) across calls;
  112: \ for simplicity we align it strictly for every group.
  113: 
  114: slowvoc @
  115: slowvoc on \ we want a linked list for the vocabulary locals
  116: vocabulary locals \ this contains the local variables
  117: ' locals >body ' locals-list >body !
  118: slowvoc !
  119: 
  120: create locals-buffer 1000 allot \ !! limited and unsafe
  121:     \ here the names of the local variables are stored
  122:     \ we would have problems storing them at the normal dp
  123: 
  124: variable locals-dp \ so here's the special dp for locals.
  125: 
  126: : alignlp-w ( n1 -- n2 )
  127:     \ cell-align size and generate the corresponding code for aligning lp
  128:     aligned dup adjust-locals-size ;
  129: 
  130: : alignlp-f ( n1 -- n2 )
  131:     faligned dup adjust-locals-size ;
  132: 
  133: \ a local declaration group (the braces stuff) is compiled by calling
  134: \ the appropriate compile-pushlocal for the locals, starting with the
  135: \ righmost local; the names are already created earlier, the
  136: \ compile-pushlocal just inserts the offsets from the frame base.
  137: 
  138: : compile-pushlocal-w ( a-addr -- ) ( run-time: w -- )
  139: \ compiles a push of a local variable, and adjusts locals-size
  140: \ stores the offset of the local variable to a-addr
  141:     locals-size @ alignlp-w cell+ dup locals-size !
  142:     swap !
  143:     postpone >l ;
  144: 
  145: : compile-pushlocal-f ( a-addr -- ) ( run-time: f -- )
  146:     locals-size @ alignlp-f float+ dup locals-size !
  147:     swap !
  148:     postpone f>l ;
  149: 
  150: : compile-pushlocal-d ( a-addr -- ) ( run-time: w1 w2 -- )
  151:     locals-size @ alignlp-w cell+ cell+ dup locals-size !
  152:     swap !
  153:     postpone swap postpone >l postpone >l ;
  154: 
  155: : compile-pushlocal-c ( a-addr -- ) ( run-time: w -- )
  156:     -1 chars compile-lp+!
  157:     locals-size @ swap !
  158:     postpone lp@ postpone c! ;
  159: 
  160: : create-local ( " name" -- a-addr )
  161:     \ defines the local "name"; the offset of the local shall be
  162:     \ stored in a-addr
  163:     create
  164: 	immediate restrict
  165: 	here 0 , ( place for the offset ) ;
  166: 
  167: : lp-offset ( n1 -- n2 )
  168: \ converts the offset from the frame start to an offset from lp and
  169: \ i.e., the address of the local is lp+locals_size-offset
  170:   locals-size @ swap - ;
  171: 
  172: : lp-offset, ( n -- )
  173: \ converts the offset from the frame start to an offset from lp and
  174: \ adds it as inline argument to a preceding locals primitive
  175:   lp-offset , ;
  176: 
  177: vocabulary locals-types \ this contains all the type specifyers, -- and }
  178: locals-types definitions
  179: 
  180: : W: ( "name" -- a-addr xt ) \ gforth w-colon
  181:     create-local
  182: 	\ xt produces the appropriate locals pushing code when executed
  183: 	['] compile-pushlocal-w
  184:     does> ( Compilation: -- ) ( Run-time: -- w )
  185:         \ compiles a local variable access
  186: 	@ lp-offset compile-@local ;
  187: 
  188: : W^ ( "name" -- a-addr xt ) \ gforth w-caret
  189:     create-local
  190: 	['] compile-pushlocal-w
  191:     does> ( Compilation: -- ) ( Run-time: -- w )
  192: 	postpone laddr# @ lp-offset, ;
  193: 
  194: : F: ( "name" -- a-addr xt ) \ gforth f-colon
  195:     create-local
  196: 	['] compile-pushlocal-f
  197:     does> ( Compilation: -- ) ( Run-time: -- w )
  198: 	@ lp-offset compile-f@local ;
  199: 
  200: : F^ ( "name" -- a-addr xt ) \ gforth f-caret
  201:     create-local
  202: 	['] compile-pushlocal-f
  203:     does> ( Compilation: -- ) ( Run-time: -- w )
  204: 	postpone laddr# @ lp-offset, ;
  205: 
  206: : D: ( "name" -- a-addr xt ) \ gforth d-colon
  207:     create-local
  208: 	['] compile-pushlocal-d
  209:     does> ( Compilation: -- ) ( Run-time: -- w )
  210: 	postpone laddr# @ lp-offset, postpone 2@ ;
  211: 
  212: : D^ ( "name" -- a-addr xt ) \ gforth d-caret
  213:     create-local
  214: 	['] compile-pushlocal-d
  215:     does> ( Compilation: -- ) ( Run-time: -- w )
  216: 	postpone laddr# @ lp-offset, ;
  217: 
  218: : C: ( "name" -- a-addr xt ) \ gforth c-colon
  219:     create-local
  220: 	['] compile-pushlocal-c
  221:     does> ( Compilation: -- ) ( Run-time: -- w )
  222: 	postpone laddr# @ lp-offset, postpone c@ ;
  223: 
  224: : C^ ( "name" -- a-addr xt ) \ gforth c-caret
  225:     create-local
  226: 	['] compile-pushlocal-c
  227:     does> ( Compilation: -- ) ( Run-time: -- w )
  228: 	postpone laddr# @ lp-offset, ;
  229: 
  230: \ you may want to make comments in a locals definitions group:
  231: ' \ alias \ immediate
  232: ' ( alias ( immediate
  233: 
  234: forth definitions
  235: 
  236: \ the following gymnastics are for declaring locals without type specifier.
  237: \ we exploit a feature of our dictionary: every wordlist
  238: \ has it's own methods for finding words etc.
  239: \ So we create a vocabulary new-locals, that creates a 'w:' local named x
  240: \ when it is asked if it contains x.
  241: 
  242: also locals-types
  243: 
  244: : new-locals-find ( caddr u w -- nfa )
  245: \ this is the find method of the new-locals vocabulary
  246: \ make a new local with name caddr u; w is ignored
  247: \ the returned nfa denotes a word that produces what W: produces
  248: \ !! do the whole thing without nextname
  249:     drop nextname
  250:     ['] W: >name ;
  251: 
  252: previous
  253: 
  254: : new-locals-reveal ( -- )
  255:   true abort" this should not happen: new-locals-reveal" ;
  256: 
  257: create new-locals-map ' new-locals-find A, ' new-locals-reveal A,
  258: 
  259: vocabulary new-locals
  260: new-locals-map ' new-locals >body cell+ A! \ !! use special access words
  261: 
  262: variable old-dpp
  263: 
  264: \ and now, finally, the user interface words
  265: : { ( -- addr wid 0 ) \ gforth open-brace
  266:     dp old-dpp !
  267:     locals-dp dpp !
  268:     also new-locals
  269:     also get-current locals definitions  locals-types
  270:     0 TO locals-wordlist
  271:     0 postpone [ ; immediate
  272: 
  273: locals-types definitions
  274: 
  275: : } ( addr wid 0 a-addr1 xt1 ... -- ) \ gforth close-brace
  276:     \ ends locals definitions
  277:     ] old-dpp @ dpp !
  278:     begin
  279: 	dup
  280:     while
  281: 	execute
  282:     repeat
  283:     drop
  284:     locals-size @ alignlp-f locals-size ! \ the strictest alignment
  285:     set-current
  286:     previous previous
  287:     locals-list TO locals-wordlist ;
  288: 
  289: : -- ( addr wid 0 ... -- ) \ gforth dash-dash
  290:     }
  291:     [char] } parse 2drop ;
  292: 
  293: forth definitions
  294: 
  295: \ A few thoughts on automatic scopes for locals and how they can be
  296: \ implemented:
  297: 
  298: \ We have to combine locals with the control structures. My basic idea
  299: \ was to start the life of a local at the declaration point. The life
  300: \ would end at any control flow join (THEN, BEGIN etc.) where the local
  301: \ is lot live on both input flows (note that the local can still live in
  302: \ other, later parts of the control flow). This would make a local live
  303: \ as long as you expected and sometimes longer (e.g. a local declared in
  304: \ a BEGIN..UNTIL loop would still live after the UNTIL).
  305: 
  306: \ The following example illustrates the problems of this approach:
  307: 
  308: \ { z }
  309: \ if
  310: \   { x }
  311: \ begin
  312: \   { y }
  313: \ [ 1 cs-roll ] then
  314: \   ...
  315: \ until
  316: 
  317: \ x lives only until the BEGIN, but the compiler does not know this
  318: \ until it compiles the UNTIL (it can deduce it at the THEN, because at
  319: \ that point x lives in no thread, but that does not help much). This is
  320: \ solved by optimistically assuming at the BEGIN that x lives, but
  321: \ warning at the UNTIL that it does not. The user is then responsible
  322: \ for checking that x is only used where it lives.
  323: 
  324: \ The produced code might look like this (leaving out alignment code):
  325: 
  326: \ >l ( z )
  327: \ ?branch <then>
  328: \ >l ( x )
  329: \ <begin>:
  330: \ >l ( y )
  331: \ lp+!# 8 ( RIP: x,y )
  332: \ <then>:
  333: \ ...
  334: \ lp+!# -4 ( adjust lp to <begin> state )
  335: \ ?branch <begin>
  336: \ lp+!# 4 ( undo adjust )
  337: 
  338: \ The BEGIN problem also has another incarnation:
  339: 
  340: \ AHEAD
  341: \ BEGIN
  342: \   x
  343: \ [ 1 CS-ROLL ] THEN
  344: \   { x }
  345: \   ...
  346: \ UNTIL
  347: 
  348: \ should be legal: The BEGIN is not a control flow join in this case,
  349: \ since it cannot be entered from the top; therefore the definition of x
  350: \ dominates the use. But the compiler processes the use first, and since
  351: \ it does not look ahead to notice the definition, it will complain
  352: \ about it. Here's another variation of this problem:
  353: 
  354: \ IF
  355: \   { x }
  356: \ ELSE
  357: \   ...
  358: \ AHEAD
  359: \ BEGIN
  360: \   x
  361: \ [ 2 CS-ROLL ] THEN
  362: \   ...
  363: \ UNTIL
  364: 
  365: \ In this case x is defined before the use, and the definition dominates
  366: \ the use, but the compiler does not know this until it processes the
  367: \ UNTIL. So what should the compiler assume does live at the BEGIN, if
  368: \ the BEGIN is not a control flow join? The safest assumption would be
  369: \ the intersection of all locals lists on the control flow
  370: \ stack. However, our compiler assumes that the same variables are live
  371: \ as on the top of the control flow stack. This covers the following case:
  372: 
  373: \ { x }
  374: \ AHEAD
  375: \ BEGIN
  376: \   x
  377: \ [ 1 CS-ROLL ] THEN
  378: \   ...
  379: \ UNTIL
  380: 
  381: \ If this assumption is too optimistic, the compiler will warn the user.
  382: 
  383: \ Implementation: migrated to kernal.fs
  384: 
  385: \ THEN (another control flow from before joins the current one):
  386: \ The new locals-list is the intersection of the current locals-list and
  387: \ the orig-local-list. The new locals-size is the (alignment-adjusted)
  388: \ size of the new locals-list. The following code is generated:
  389: \ lp+!# (current-locals-size - orig-locals-size)
  390: \ <then>:
  391: \ lp+!# (orig-locals-size - new-locals-size)
  392: 
  393: \ Of course "lp+!# 0" is not generated. Still this is admittedly a bit
  394: \ inefficient, e.g. if there is a locals declaration between IF and
  395: \ ELSE. However, if ELSE generates an appropriate "lp+!#" before the
  396: \ branch, there will be none after the target <then>.
  397: 
  398: \ explicit scoping
  399: 
  400: : scope ( compilation  -- scope ; run-time  -- ) \ gforth
  401:  cs-push-part scopestart ; immediate
  402: 
  403: : endscope ( compilation scope -- ; run-time  -- ) \ gforth
  404:  scope?
  405:  drop
  406:  locals-list @ common-list
  407:  dup list-size adjust-locals-size
  408:  locals-list ! ; immediate
  409: 
  410: \ adapt the hooks
  411: 
  412: : locals-:-hook ( sys -- sys addr xt n )
  413:     \ addr is the nfa of the defined word, xt its xt
  414:     DEFERS :-hook
  415:     last @ lastcfa @
  416:     clear-leave-stack
  417:     0 locals-size !
  418:     locals-buffer locals-dp !
  419:     0 locals-list !
  420:     dead-code off
  421:     defstart ;
  422: 
  423: : locals-;-hook ( sys addr xt sys -- sys )
  424:     def?
  425:     0 TO locals-wordlist
  426:     0 adjust-locals-size ( not every def ends with an exit )
  427:     lastcfa ! last !
  428:     DEFERS ;-hook ;
  429: 
  430: ' locals-:-hook IS :-hook
  431: ' locals-;-hook IS ;-hook
  432: 
  433: \ The words in the locals dictionary space are not deleted until the end
  434: \ of the current word. This is a bit too conservative, but very simple.
  435: 
  436: \ There are a few cases to consider: (see above)
  437: 
  438: \ after AGAIN, AHEAD, EXIT (the current control flow is dead):
  439: \ We have to special-case the above cases against that. In this case the
  440: \ things above are not control flow joins. Everything should be taken
  441: \ over from the live flow. No lp+!# is generated.
  442: 
  443: \ !! The lp gymnastics for UNTIL are also a real problem: locals cannot be
  444: \ used in signal handlers (or anything else that may be called while
  445: \ locals live beyond the lp) without changing the locals stack.
  446: 
  447: \ About warning against uses of dead locals. There are several options:
  448: 
  449: \ 1) Do not complain (After all, this is Forth;-)
  450: 
  451: \ 2) Additional restrictions can be imposed so that the situation cannot
  452: \ arise; the programmer would have to introduce explicit scoping
  453: \ declarations in cases like the above one. I.e., complain if there are
  454: \ locals that are live before the BEGIN but not before the corresponding
  455: \ AGAIN (replace DO etc. for BEGIN and UNTIL etc. for AGAIN).
  456: 
  457: \ 3) The real thing: i.e. complain, iff a local lives at a BEGIN, is
  458: \ used on a path starting at the BEGIN, and does not live at the
  459: \ corresponding AGAIN. This is somewhat hard to implement. a) How does
  460: \ the compiler know when it is working on a path starting at a BEGIN
  461: \ (consider "{ x } if begin [ 1 cs-roll ] else x endif again")? b) How
  462: \ is the usage info stored?
  463: 
  464: \ For now I'll resort to alternative 2. When it produces warnings they
  465: \ will often be spurious, but warnings should be rare. And better
  466: \ spurious warnings now and then than days of bug-searching.
  467: 
  468: \ Explicit scoping of locals is implemented by cs-pushing the current
  469: \ locals-list and -size (and an unused cell, to make the size equal to
  470: \ the other entries) at the start of the scope, and restoring them at
  471: \ the end of the scope to the intersection, like THEN does.
  472: 
  473: 
  474: \ And here's finally the ANS standard stuff
  475: 
  476: : (local) ( addr u -- ) \ local paren-local-paren
  477:     \ a little space-inefficient, but well deserved ;-)
  478:     \ In exchange, there are no restrictions whatsoever on using (local)
  479:     \ as long as you use it in a definition
  480:     dup
  481:     if
  482: 	nextname POSTPONE { [ also locals-types ] W: } [ previous ]
  483:     else
  484: 	2drop
  485:     endif ;
  486: 
  487: : >definer ( xt -- definer )
  488:     \ this gives a unique identifier for the way the xt was defined
  489:     \ words defined with different does>-codes have different definers
  490:     \ the definer can be used for comparison and in definer!
  491:     dup >code-address [ ' spaces >code-address ] Literal =
  492:     \ !! this definition will not work on some implementations for `bits'
  493:     if  \ if >code-address delivers the same value for all does>-def'd words
  494: 	>does-code 1 or \ bit 0 marks special treatment for does codes
  495:     else
  496: 	>code-address
  497:     then ;
  498: 
  499: : definer! ( definer xt -- )
  500:     \ gives the word represented by xt the behaviour associated with definer
  501:     over 1 and if
  502: 	swap [ 1 invert ] literal and does-code!
  503:     else
  504: 	code-address!
  505:     then ;
  506: 
  507: : TO ( c|w|d|r "name" -- ) \ core-ext,local
  508: \ !! state smart
  509:  0 0 0. 0.0e0 { c: clocal w: wlocal d: dlocal f: flocal }
  510:  ' dup >definer
  511:  state @ 
  512:  if
  513:    case
  514:      [ ' locals-wordlist >definer ] literal \ value
  515:      OF >body POSTPONE Aliteral POSTPONE ! ENDOF
  516:      [ ' clocal >definer ] literal
  517:      OF POSTPONE laddr# >body @ lp-offset, POSTPONE c! ENDOF
  518:      [ ' wlocal >definer ] literal
  519:      OF POSTPONE laddr# >body @ lp-offset, POSTPONE ! ENDOF
  520:      [ ' dlocal >definer ] literal
  521:      OF POSTPONE laddr# >body @ lp-offset, POSTPONE 2! ENDOF
  522:      [ ' flocal >definer ] literal
  523:      OF POSTPONE laddr# >body @ lp-offset, POSTPONE f! ENDOF
  524:      -&32 throw
  525:    endcase
  526:  else
  527:    [ ' locals-wordlist >definer ] literal =
  528:    if
  529:      >body !
  530:    else
  531:      -&32 throw
  532:    endif
  533:  endif ; immediate
  534: 
  535: : locals|
  536:     \ don't use 'locals|'! use '{'! A portable and free '{'
  537:     \ implementation is anslocals.fs
  538:     BEGIN
  539: 	name 2dup s" |" compare 0<>
  540:     WHILE
  541: 	(local)
  542:     REPEAT
  543:     drop 0 (local) ; immediate restrict