File:  [gforth] / gforth / glocals.fs
Revision 1.7: download - view: text, annotated - select for diffs
Mon Sep 12 19:00:30 1994 UTC (26 years, 2 months ago) by pazsan
Branches: MAIN
CVS tags: HEAD
Added forth variants for primitives
Added a generator for forth primitives
Cleaned up some minor errors
Changed names of local access (was cell size dependent)
Where is "getopt.h"???!? Added tiny workaround. Where is getopt_long?

    1: \ Local variables are quite important for writing readable programs, but
    2: \ IMO (anton) they are the worst part of the standard. There they are very
    3: \ restricted and have an ugly interface.
    4: 
    5: \ So, we implement the locals wordset, but do not recommend using
    6: \ locals-ext (which is a really bad user interface for locals).
    7: 
    8: \ We also have a nice and powerful user-interface for locals: locals are
    9: \ defined with
   10: 
   11: \ { local1 local2 ... }
   12: \ or
   13: \ { local1 local2 ... -- ... }
   14: \ (anything after the -- is just a comment)
   15: 
   16: \ Every local in this list consists of an optional type specification
   17: \ and a name. If there is only the name, it stands for a cell-sized
   18: \ value (i.e., you get the value of the local variable, not it's
   19: \ address). The following type specifiers stand before the name:
   20: 
   21: \ Specifier	Type	Access
   22: \ W:		Cell	value
   23: \ W^		Cell	address
   24: \ D:		Double	value
   25: \ D^		Double	address
   26: \ F:		Float	value
   27: \ F^		Float	address
   28: \ C:		Char	value
   29: \ C^		Char	address
   30: 
   31: \ The local variables are initialized with values from the appropriate
   32: \ stack. In contrast to the examples in the standard document our locals
   33: \ take the arguments in the expected way: The last local gets the top of
   34: \ stack, the second last gets the second stack item etc. An example:
   35: 
   36: \ : CX* { F: Ar  F: Ai  F: Br  F: Bi -- Cr Ci }
   37: \ \ complex multiplication
   38: \  Ar Br f* Ai Bi f* f-
   39: \  Ar Bi f* Ai Br f* f+ ;
   40: 
   41: \ There will also be a way to add user types, but it is not yet decided,
   42: \ how. Ideas are welcome.
   43: 
   44: \ Locals defined in this manner live until (!! see below). 
   45: \ Their names can be used during this time to get
   46: \ their value or address; The addresses produced in this way become
   47: \ invalid at the end of the lifetime.
   48: 
   49: \ Values can be changed with TO, but this is not recomended (TO is a
   50: \ kludge and words lose the single-assignment property, which makes them
   51: \ harder to analyse).
   52: 
   53: \ As for the internals, we use a special locals stack. This eliminates
   54: \ the problems and restrictions of reusing the return stack and allows
   55: \ to store floats as locals: the return stack is not guaranteed to be
   56: \ aligned correctly, but our locals stack must be float-aligned between
   57: \ words.
   58: 
   59: \ Other things about the internals are pretty unclear now.
   60: 
   61: \ Currently locals may only be
   62: \ defined at the outer level and TO is not supported.
   63: 
   64: include search-order.fs
   65: include float.fs
   66: 
   67: : compile-@local ( n -- )
   68:  case
   69:     0       of postpone @local0 endof
   70:     1 cells of postpone @local1 endof
   71:     2 cells of postpone @local2 endof
   72:     3 cells of postpone @local3 endof
   73:    ( otherwise ) dup postpone @local# ,
   74:  endcase ;
   75: 
   76: : compile-f@local ( n -- )
   77:  case
   78:     0        of postpone f@local0 endof
   79:     1 floats of postpone f@local1 endof
   80:    ( otherwise ) dup postpone f@local# ,
   81:  endcase ;
   82: 
   83: \ the locals stack grows downwards (see primitives)
   84: \ of the local variables of a group (in braces) the leftmost is on top,
   85: \ i.e. by going onto the locals stack the order is reversed.
   86: \ there are alignment gaps if necessary.
   87: \ lp must have the strictest alignment (usually float) across calls;
   88: \ for simplicity we align it strictly for every group.
   89: 
   90: slowvoc @
   91: slowvoc on \ we want a linked list for the vocabulary locals
   92: vocabulary locals \ this contains the local variables
   93: ' locals >body ' locals-list >body !
   94: slowvoc !
   95: 
   96: create locals-buffer 1000 allot \ !! limited and unsafe
   97:     \ here the names of the local variables are stored
   98:     \ we would have problems storing them at the normal dp
   99: 
  100: variable locals-dp \ so here's the special dp for locals.
  101: 
  102: : alignlp-w ( n1 -- n2 )
  103:     \ cell-align size and generate the corresponding code for aligning lp
  104:     aligned dup adjust-locals-size ;
  105: 
  106: : alignlp-f ( n1 -- n2 )
  107:     faligned dup adjust-locals-size ;
  108: 
  109: \ a local declaration group (the braces stuff) is compiled by calling
  110: \ the appropriate compile-pushlocal for the locals, starting with the
  111: \ righmost local; the names are already created earlier, the
  112: \ compile-pushlocal just inserts the offsets from the frame base.
  113: 
  114: : compile-pushlocal-w ( a-addr -- ) ( run-time: w -- )
  115: \ compiles a push of a local variable, and adjusts locals-size
  116: \ stores the offset of the local variable to a-addr
  117:     locals-size @ alignlp-w cell+ dup locals-size !
  118:     swap !
  119:     postpone >l ;
  120: 
  121: : compile-pushlocal-f ( a-addr -- ) ( run-time: f -- )
  122:     locals-size @ alignlp-f float+ dup locals-size !
  123:     swap !
  124:     postpone f>l ;
  125: 
  126: : compile-pushlocal-d ( a-addr -- ) ( run-time: w1 w2 -- )
  127:     locals-size @ alignlp-w cell+ cell+ dup locals-size !
  128:     swap !
  129:     postpone swap postpone >l postpone >l ;
  130: 
  131: : compile-pushlocal-c ( a-addr -- ) ( run-time: w -- )
  132:     -1 chars compile-lp+!
  133:     locals-size @ swap !
  134:     postpone lp@ postpone c! ;
  135: 
  136: : create-local ( " name" -- a-addr )
  137: 	\ defines the local "name"; the offset of the local shall be stored in a-addr
  138:     create
  139: 	immediate
  140: 	here 0 , ( place for the offset ) ;
  141: 
  142: : lp-offset ( n1 -- n2 )
  143: \ converts the offset from the frame start to an offset from lp and
  144: \ i.e., the address of the local is lp+locals_size-offset
  145:   locals-size @ swap - ;
  146: 
  147: : lp-offset, ( n -- )
  148: \ converts the offset from the frame start to an offset from lp and
  149: \ adds it as inline argument to a preceding locals primitive
  150:   lp-offset , ;
  151: 
  152: vocabulary locals-types \ this contains all the type specifyers, -- and }
  153: locals-types definitions
  154: 
  155: : W:
  156:     create-local ( "name" -- a-addr xt )
  157: 	\ xt produces the appropriate locals pushing code when executed
  158: 	['] compile-pushlocal-w
  159:     does> ( Compilation: -- ) ( Run-time: -- w )
  160:         \ compiles a local variable access
  161: 	@ lp-offset compile-@local ;
  162: 
  163: : W^
  164:     create-local ( "name" -- a-addr xt )
  165: 	['] compile-pushlocal-w
  166:     does> ( Compilation: -- ) ( Run-time: -- w )
  167: 	postpone laddr# @ lp-offset, ;
  168: 
  169: : F:
  170:     create-local ( "name" -- a-addr xt )
  171: 	['] compile-pushlocal-f
  172:     does> ( Compilation: -- ) ( Run-time: -- w )
  173: 	@ lp-offset compile-f@local ;
  174: 
  175: : F^
  176:     create-local ( "name" -- a-addr xt )
  177: 	['] compile-pushlocal-f
  178:     does> ( Compilation: -- ) ( Run-time: -- w )
  179: 	postpone laddr# @ lp-offset, ;
  180: 
  181: : D:
  182:     create-local ( "name" -- a-addr xt )
  183: 	['] compile-pushlocal-d
  184:     does> ( Compilation: -- ) ( Run-time: -- w )
  185: 	postpone laddr# @ lp-offset, postpone 2@ ;
  186: 
  187: : D^
  188:     create-local ( "name" -- a-addr xt )
  189: 	['] compile-pushlocal-d
  190:     does> ( Compilation: -- ) ( Run-time: -- w )
  191: 	postpone laddr# @ lp-offset, ;
  192: 
  193: : C:
  194:     create-local ( "name" -- a-addr xt )
  195: 	['] compile-pushlocal-c
  196:     does> ( Compilation: -- ) ( Run-time: -- w )
  197: 	postpone laddr# @ lp-offset, postpone c@ ;
  198: 
  199: : C^
  200:     create-local ( "name" -- a-addr xt )
  201: 	['] compile-pushlocal-c
  202:     does> ( Compilation: -- ) ( Run-time: -- w )
  203: 	postpone laddr# @ lp-offset, ;
  204: 
  205: \ you may want to make comments in a locals definitions group:
  206: ' \ alias \ immediate
  207: ' ( alias ( immediate
  208: 
  209: forth definitions
  210: 
  211: \ the following gymnastics are for declaring locals without type specifier.
  212: \ we exploit a feature of our dictionary: every wordlist
  213: \ has it's own methods for finding words etc.
  214: \ So we create a vocabulary new-locals, that creates a 'w:' local named x
  215: \ when it is asked if it contains x.
  216: 
  217: also locals-types
  218: 
  219: : new-locals-find ( caddr u w -- nfa )
  220: \ this is the find method of the new-locals vocabulary
  221: \ make a new local with name caddr u; w is ignored
  222: \ the returned nfa denotes a word that produces what W: produces
  223: \ !! do the whole thing without nextname
  224:     drop nextname
  225:     ['] W: >name ;
  226: 
  227: previous
  228: 
  229: : new-locals-reveal ( -- )
  230:   true abort" this should not happen: new-locals-reveal" ;
  231: 
  232: create new-locals-map ' new-locals-find A, ' new-locals-reveal A,
  233: 
  234: vocabulary new-locals
  235: new-locals-map ' new-locals >body cell+ A! \ !! use special access words
  236: 
  237: variable old-dpp
  238: 
  239: \ and now, finally, the user interface words
  240: : { ( -- addr wid 0 )
  241:     dp old-dpp !
  242:     locals-dp dpp !
  243:     also new-locals
  244:     also get-current locals definitions  locals-types
  245:     0 TO locals-wordlist
  246:     0 postpone [ ; immediate
  247: 
  248: locals-types definitions
  249: 
  250: : } ( addr wid 0 a-addr1 xt1 ... -- )
  251:     \ ends locals definitions
  252:     ] old-dpp @ dpp !
  253:     begin
  254: 	dup
  255:     while
  256: 	execute
  257:     repeat
  258:     drop
  259:     locals-size @ alignlp-f locals-size ! \ the strictest alignment
  260:     set-current
  261:     previous previous
  262:     locals-list TO locals-wordlist ;
  263: 
  264: : -- ( addr wid 0 ... -- )
  265:     }
  266:     [char] } word drop ;
  267: 
  268: forth definitions
  269: 
  270: \ A few thoughts on automatic scopes for locals and how they can be
  271: \ implemented:
  272: 
  273: \ We have to combine locals with the control structures. My basic idea
  274: \ was to start the life of a local at the declaration point. The life
  275: \ would end at any control flow join (THEN, BEGIN etc.) where the local
  276: \ is lot live on both input flows (note that the local can still live in
  277: \ other, later parts of the control flow). This would make a local live
  278: \ as long as you expected and sometimes longer (e.g. a local declared in
  279: \ a BEGIN..UNTIL loop would still live after the UNTIL).
  280: 
  281: \ The following example illustrates the problems of this approach:
  282: 
  283: \ { z }
  284: \ if
  285: \   { x }
  286: \ begin
  287: \   { y }
  288: \ [ 1 cs-roll ] then
  289: \   ...
  290: \ until
  291: 
  292: \ x lives only until the BEGIN, but the compiler does not know this
  293: \ until it compiles the UNTIL (it can deduce it at the THEN, because at
  294: \ that point x lives in no thread, but that does not help much). This is
  295: \ solved by optimistically assuming at the BEGIN that x lives, but
  296: \ warning at the UNTIL that it does not. The user is then responsible
  297: \ for checking that x is only used where it lives.
  298: 
  299: \ The produced code might look like this (leaving out alignment code):
  300: 
  301: \ >l ( z )
  302: \ ?branch <then>
  303: \ >l ( x )
  304: \ <begin>:
  305: \ >l ( y )
  306: \ lp+!# 8 ( RIP: x,y )
  307: \ <then>:
  308: \ ...
  309: \ lp+!# -4 ( adjust lp to <begin> state )
  310: \ ?branch <begin>
  311: \ lp+!# 4 ( undo adjust )
  312: 
  313: \ The BEGIN problem also has another incarnation:
  314: 
  315: \ AHEAD
  316: \ BEGIN
  317: \   x
  318: \ [ 1 CS-ROLL ] THEN
  319: \   { x }
  320: \   ...
  321: \ UNTIL
  322: 
  323: \ should be legal: The BEGIN is not a control flow join in this case,
  324: \ since it cannot be entered from the top; therefore the definition of x
  325: \ dominates the use. But the compiler processes the use first, and since
  326: \ it does not look ahead to notice the definition, it will complain
  327: \ about it. Here's another variation of this problem:
  328: 
  329: \ IF
  330: \   { x }
  331: \ ELSE
  332: \   ...
  333: \ AHEAD
  334: \ BEGIN
  335: \   x
  336: \ [ 2 CS-ROLL ] THEN
  337: \   ...
  338: \ UNTIL
  339: 
  340: \ In this case x is defined before the use, and the definition dominates
  341: \ the use, but the compiler does not know this until it processes the
  342: \ UNTIL. So what should the compiler assume does live at the BEGIN, if
  343: \ the BEGIN is not a control flow join? The safest assumption would be
  344: \ the intersection of all locals lists on the control flow
  345: \ stack. However, our compiler assumes that the same variables are live
  346: \ as on the top of the control flow stack. This covers the following case:
  347: 
  348: \ { x }
  349: \ AHEAD
  350: \ BEGIN
  351: \   x
  352: \ [ 1 CS-ROLL ] THEN
  353: \   ...
  354: \ UNTIL
  355: 
  356: \ If this assumption is too optimistic, the compiler will warn the user.
  357: 
  358: \ Implementation: migrated to kernal.fs
  359: 
  360: \ THEN (another control flow from before joins the current one):
  361: \ The new locals-list is the intersection of the current locals-list and
  362: \ the orig-local-list. The new locals-size is the (alignment-adjusted)
  363: \ size of the new locals-list. The following code is generated:
  364: \ lp+!# (current-locals-size - orig-locals-size)
  365: \ <then>:
  366: \ lp+!# (orig-locals-size - new-locals-size)
  367: 
  368: \ Of course "lp+!# 0" is not generated. Still this is admittedly a bit
  369: \ inefficient, e.g. if there is a locals declaration between IF and
  370: \ ELSE. However, if ELSE generates an appropriate "lp+!#" before the
  371: \ branch, there will be none after the target <then>.
  372: 
  373: \ explicit scoping
  374: 
  375: : scope ( -- scope )
  376:  cs-push-part scopestart ; immediate
  377: 
  378: : endscope ( scope -- )
  379:  scope?
  380:  drop
  381:  locals-list @ common-list
  382:  dup list-size adjust-locals-size
  383:  locals-list ! ; immediate
  384: 
  385: \ adapt the hooks
  386: 
  387: : locals-:-hook ( sys -- sys addr xt n )
  388:     \ addr is the nfa of the defined word, xt its xt
  389:     DEFERS :-hook
  390:     last @ lastcfa @
  391:     clear-leave-stack
  392:     0 locals-size !
  393:     locals-buffer locals-dp !
  394:     0 locals-list !
  395:     dead-code off
  396:     defstart ;
  397: 
  398: : locals-;-hook ( sys addr xt sys -- sys )
  399:     def?
  400:     0 TO locals-wordlist
  401:     0 adjust-locals-size ( not every def ends with an exit )
  402:     lastcfa ! last !
  403:     DEFERS ;-hook ;
  404: 
  405: ' locals-:-hook IS :-hook
  406: ' locals-;-hook IS ;-hook
  407: 
  408: \ The words in the locals dictionary space are not deleted until the end
  409: \ of the current word. This is a bit too conservative, but very simple.
  410: 
  411: \ There are a few cases to consider: (see above)
  412: 
  413: \ after AGAIN, AHEAD, EXIT (the current control flow is dead):
  414: \ We have to special-case the above cases against that. In this case the
  415: \ things above are not control flow joins. Everything should be taken
  416: \ over from the live flow. No lp+!# is generated.
  417: 
  418: \ !! The lp gymnastics for UNTIL are also a real problem: locals cannot be
  419: \ used in signal handlers (or anything else that may be called while
  420: \ locals live beyond the lp) without changing the locals stack.
  421: 
  422: \ About warning against uses of dead locals. There are several options:
  423: 
  424: \ 1) Do not complain (After all, this is Forth;-)
  425: 
  426: \ 2) Additional restrictions can be imposed so that the situation cannot
  427: \ arise; the programmer would have to introduce explicit scoping
  428: \ declarations in cases like the above one. I.e., complain if there are
  429: \ locals that are live before the BEGIN but not before the corresponding
  430: \ AGAIN (replace DO etc. for BEGIN and UNTIL etc. for AGAIN).
  431: 
  432: \ 3) The real thing: i.e. complain, iff a local lives at a BEGIN, is
  433: \ used on a path starting at the BEGIN, and does not live at the
  434: \ corresponding AGAIN. This is somewhat hard to implement. a) How does
  435: \ the compiler know when it is working on a path starting at a BEGIN
  436: \ (consider "{ x } if begin [ 1 cs-roll ] else x endif again")? b) How
  437: \ is the usage info stored?
  438: 
  439: \ For now I'll resort to alternative 2. When it produces warnings they
  440: \ will often be spurious, but warnings should be rare. And better
  441: \ spurious warnings now and then than days of bug-searching.
  442: 
  443: \ Explicit scoping of locals is implemented by cs-pushing the current
  444: \ locals-list and -size (and an unused cell, to make the size equal to
  445: \ the other entries) at the start of the scope, and restoring them at
  446: \ the end of the scope to the intersection, like THEN does.
  447: 
  448: 
  449: \ And here's finally the ANS standard stuff
  450: 
  451: : (local) ( addr u -- )
  452:     \ a little space-inefficient, but well deserved ;-)
  453:     \ In exchange, there are no restrictions whatsoever on using (local)
  454:     \ as long as you use it in a definition
  455:     dup
  456:     if
  457: 	nextname POSTPONE { [ also locals-types ] W: } [ previous ]
  458:     else
  459: 	2drop
  460:     endif ;
  461: 
  462: : >definer ( xt -- definer )
  463:     \ this gives a unique identifier for the way the xt was defined
  464:     \ words defined with different does>-codes have different definers
  465:     \ the definer can be used for comparison and in definer!
  466:     dup >code-address [ ' bits >code-address ] Literal =
  467:     \ !! this definition will not work on some implementations for `bits'
  468:     if  \ if >code-address delivers the same value for all does>-def'd words
  469: 	>does-code 1 or \ bit 0 marks special treatment for does codes
  470:     else
  471: 	>code-address
  472:     then ;
  473: 
  474: : definer! ( definer xt -- )
  475:     \ gives the word represented by xt the behaviour associated with definer
  476:     over 1 and if
  477: 	does-code!
  478:     else
  479: 	code-address!
  480:     then ;
  481: 
  482: \ !! untested
  483: : TO ( c|w|d|r "name" -- )
  484: \ !! state smart
  485:  0 0 0. 0.0e0 { c: clocal w: wlocal d: dlocal f: flocal }
  486:  ' dup >definer
  487:  state @ 
  488:  if
  489:    case
  490:      [ ' locals-wordlist >definer ] literal \ value
  491:      OF >body POSTPONE Aliteral POSTPONE ! ENDOF
  492:      [ ' clocal >definer ] literal
  493:      OF POSTPONE laddr# >body @ lp-offset, POSTPONE c! ENDOF
  494:      [ ' wlocal >definer ] literal
  495:      OF POSTPONE laddr# >body @ lp-offset, POSTPONE ! ENDOF
  496:      [ ' dlocal >definer ] literal
  497:      OF POSTPONE laddr# >body @ lp-offset, POSTPONE d! ENDOF
  498:      [ ' flocal >definer ] literal
  499:      OF POSTPONE laddr# >body @ lp-offset, POSTPONE f! ENDOF
  500:      abort" can only store TO value or local value"
  501:    endcase
  502:  else
  503:    [ ' locals-wordlist >definer ] literal =
  504:    if
  505:      >body !
  506:    else
  507:      abort" can only store TO value"
  508:    endif
  509:  endif ; immediate
  510: 
  511: : locals|
  512:   BEGIN  name 2dup s" |" compare 0=  WHILE
  513:          (local)  REPEAT  drop 0 (local) ;  immediate restrict

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