File:  [gforth] / gforth / Attic / conditionals.fs
Revision 1.4: download - view: text, annotated - select for diffs
Wed Mar 19 18:27:12 1997 UTC (25 years, 3 months ago) by anton
Branches: MAIN
CVS tags: v0-3-0, HEAD
fixed some documentation bugs
updated dates on copyright messages
updated NEWS
some fixes in Makefile.in

    1: \ Structural Conditionals                              12dec92py
    2: 
    3: \ Copyright (C) 1995-1997 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: here 0 , \ just a dummy, the real value of locals-list is patched into it in glocals.fs
   22: AConstant locals-list \ acts like a variable that contains
   23: 		      \ a linear list of locals names
   24: 
   25: 
   26: variable dead-code \ true if normal code at "here" would be dead
   27: variable backedge-locals
   28:     \ contains the locals list that BEGIN will assume to be live on
   29:     \ the back edge if the BEGIN is unreachable from above. Set by
   30:     \ ASSUME-LIVE, reset by UNREACHABLE.
   31: 
   32: : UNREACHABLE ( -- ) \ gforth
   33:     \ declares the current point of execution as unreachable
   34:     dead-code on
   35:     0 backedge-locals ! ; immediate
   36: 
   37: : ASSUME-LIVE ( orig -- orig ) \ gforth
   38:     \ used immediatly before a BEGIN that is not reachable from
   39:     \ above.  causes the BEGIN to assume that the same locals are live
   40:     \ as at the orig point
   41:     dup orig?
   42:     2 pick backedge-locals ! ; immediate
   43:     
   44: \ Control Flow Stack
   45: \ orig, etc. have the following structure:
   46: \ type ( defstart, live-orig, dead-orig, dest, do-dest, scopestart) ( TOS )
   47: \ address (of the branch or the instruction to be branched to) (second)
   48: \ locals-list (valid at address) (third)
   49: 
   50: \ types
   51: 0 constant defstart
   52: 1 constant live-orig
   53: 2 constant dead-orig
   54: 3 constant dest \ the loopback branch is always assumed live
   55: 4 constant do-dest
   56: 5 constant scopestart
   57: 
   58: : def? ( n -- )
   59:     defstart <> abort" unstructured " ;
   60: 
   61: : orig? ( n -- )
   62:  dup live-orig <> swap dead-orig <> and abort" expected orig " ;
   63: 
   64: : dest? ( n -- )
   65:  dest <> abort" expected dest " ;
   66: 
   67: : do-dest? ( n -- )
   68:  do-dest <> abort" expected do-dest " ;
   69: 
   70: : scope? ( n -- )
   71:  scopestart <> abort" expected scope " ;
   72: 
   73: : non-orig? ( n -- )
   74:  dest scopestart 1+ within 0= abort" expected dest, do-dest or scope" ;
   75: 
   76: : cs-item? ( n -- )
   77:  live-orig scopestart 1+ within 0= abort" expected control flow stack item" ;
   78: 
   79: 3 constant cs-item-size
   80: 
   81: : CS-PICK ( ... u -- ... destu ) \ tools-ext
   82:  1+ cs-item-size * 1- >r
   83:  r@ pick  r@ pick  r@ pick
   84:  rdrop
   85:  dup non-orig? ;
   86: 
   87: : CS-ROLL ( destu/origu .. dest0/orig0 u -- .. dest0/orig0 destu/origu ) \ tools-ext
   88:  1+ cs-item-size * 1- >r
   89:  r@ roll r@ roll r@ roll
   90:  rdrop
   91:  dup cs-item? ; 
   92: 
   93: : cs-push-part ( -- list addr )
   94:  locals-list @ here ;
   95: 
   96: : cs-push-orig ( -- orig )
   97:  cs-push-part dead-code @
   98:  if
   99:    dead-orig
  100:  else
  101:    live-orig
  102:  then ;   
  103: 
  104: \ Structural Conditionals                              12dec92py
  105: 
  106: : ?struc      ( flag -- )       abort" unstructured " ;
  107: : sys?        ( sys -- )        dup 0= ?struc ;
  108: : >mark ( -- orig )
  109:  cs-push-orig 0 , ;
  110: : >resolve    ( addr -- )        here over - swap ! ;
  111: : <resolve    ( addr -- )        here - , ;
  112: 
  113: : BUT
  114:     1 cs-roll ;                      immediate restrict
  115: : YET
  116:     0 cs-pick ;                       immediate restrict
  117: 
  118: \ Structural Conditionals                              12dec92py
  119: 
  120: : AHEAD ( compilation -- orig ; run-time -- ) \ tools-ext
  121:     POSTPONE branch  >mark  POSTPONE unreachable ; immediate restrict
  122: 
  123: : IF ( compilation -- orig ; run-time f -- ) \ core
  124:  POSTPONE ?branch >mark ; immediate restrict
  125: 
  126: : ?DUP-IF ( compilation -- orig ; run-time n -- n| ) \ gforth	question-dupe-if
  127: \G This is the preferred alternative to the idiom "?DUP IF", since it can be
  128: \G better handled by tools like stack checkers. Besides, it's faster.
  129:     POSTPONE ?dup-?branch >mark ;       immediate restrict
  130: 
  131: : ?DUP-0=-IF ( compilation -- orig ; run-time n -- n| ) \ gforth	question-dupe-zero-equals-if
  132:     POSTPONE ?dup-0=-?branch >mark ;       immediate restrict
  133: 
  134: Defer then-like ( orig -- )
  135: : cs>addr ( orig/dest -- )  drop >resolve drop ;
  136: ' cs>addr IS then-like
  137: 
  138: : THEN ( compilation orig -- ; run-time -- ) \ core
  139:     dup orig?  then-like ; immediate restrict
  140: 
  141: ' THEN alias ENDIF ( compilation orig -- ; run-time -- ) \ gforth
  142: immediate restrict
  143: \ Same as "THEN". This is what you use if your program will be seen by
  144: \ people who have not been brought up with Forth (or who have been
  145: \ brought up with fig-Forth).
  146: 
  147: : ELSE ( compilation orig1 -- orig2 ; run-time f -- ) \ core
  148:     POSTPONE ahead
  149:     1 cs-roll
  150:     POSTPONE then ; immediate restrict
  151: 
  152: Defer begin-like ( -- )
  153: ' noop IS begin-like
  154: 
  155: : BEGIN ( compilation -- dest ; run-time -- ) \ core
  156:     begin-like cs-push-part dest ; immediate restrict
  157: 
  158: Defer again-like ( dest -- addr )
  159: ' nip IS again-like
  160: 
  161: : AGAIN ( compilation dest -- ; run-time -- ) \ core-ext
  162:     dest? again-like  POSTPONE branch  <resolve ; immediate restrict
  163: 
  164: Defer until-like
  165: : until, ( list addr xt1 xt2 -- )  drop compile, <resolve drop ;
  166: ' until, IS until-like
  167: 
  168: : UNTIL ( compilation dest -- ; run-time f -- ) \ core
  169:     dest? ['] ?branch ['] ?branch-lp+!# until-like ; immediate restrict
  170: 
  171: : WHILE ( compilation dest -- orig dest ; run-time f -- ) \ core
  172:     POSTPONE if
  173:     1 cs-roll ; immediate restrict
  174: 
  175: : REPEAT ( compilation orig dest -- ; run-time -- ) \ core
  176:     POSTPONE again
  177:     POSTPONE then ; immediate restrict
  178: 
  179: \ counted loops
  180: 
  181: \ leave poses a little problem here
  182: \ we have to store more than just the address of the branch, so the
  183: \ traditional linked list approach is no longer viable.
  184: \ This is solved by storing the information about the leavings in a
  185: \ special stack.
  186: 
  187: \ !! remove the fixed size limit. 'Tis not hard.
  188: 20 constant leave-stack-size
  189: create leave-stack  60 cells allot
  190: Avariable leave-sp  leave-stack 3 cells + leave-sp !
  191: 
  192: : clear-leave-stack ( -- )
  193:     leave-stack leave-sp ! ;
  194: 
  195: \ : leave-empty? ( -- f )
  196: \  leave-sp @ leave-stack = ;
  197: 
  198: : >leave ( orig -- )
  199:     \ push on leave-stack
  200:     leave-sp @
  201:     dup [ leave-stack 60 cells + ] Aliteral
  202:     >= abort" leave-stack full"
  203:     tuck ! cell+
  204:     tuck ! cell+
  205:     tuck ! cell+
  206:     leave-sp ! ;
  207: 
  208: : leave> ( -- orig )
  209:     \ pop from leave-stack
  210:     leave-sp @
  211:     dup leave-stack <= IF
  212:        drop 0 0 0  EXIT  THEN
  213:     cell - dup @ swap
  214:     cell - dup @ swap
  215:     cell - dup @ swap
  216:     leave-sp ! ;
  217: 
  218: : DONE ( compilation orig -- ; run-time -- ) \ gforth
  219:     \ !! the original done had ( addr -- )
  220:     drop >r drop
  221:     begin
  222: 	leave>
  223: 	over r@ u>=
  224:     while
  225: 	POSTPONE then
  226:     repeat
  227:     >leave rdrop ; immediate restrict
  228: 
  229: : LEAVE ( compilation -- ; run-time loop-sys -- ) \ core
  230:     POSTPONE ahead
  231:     >leave ; immediate restrict
  232: 
  233: : ?LEAVE ( compilation -- ; run-time f | f loop-sys -- ) \ gforth	question-leave
  234:     POSTPONE 0= POSTPONE if
  235:     >leave ; immediate restrict
  236: 
  237: : DO ( compilation -- do-sys ; run-time w1 w2 -- loop-sys ) \ core
  238:     POSTPONE (do)
  239:     POSTPONE begin drop do-dest
  240:     ( 0 0 0 >leave ) ; immediate restrict
  241: 
  242: : ?do-like ( -- do-sys )
  243:     ( 0 0 0 >leave )
  244:     >mark >leave
  245:     POSTPONE begin drop do-dest ;
  246: 
  247: : ?DO ( compilation -- do-sys ; run-time w1 w2 -- | loop-sys )	\ core-ext	question-do
  248:     POSTPONE (?do) ?do-like ; immediate restrict
  249: 
  250: : +DO ( compilation -- do-sys ; run-time n1 n2 -- | loop-sys )	\ gforth	plus-do
  251:     POSTPONE (+do) ?do-like ; immediate restrict
  252: 
  253: : U+DO ( compilation -- do-sys ; run-time u1 u2 -- | loop-sys )	\ gforth	u-plus-do
  254:     POSTPONE (u+do) ?do-like ; immediate restrict
  255: 
  256: : -DO ( compilation -- do-sys ; run-time n1 n2 -- | loop-sys )	\ gforth	minus-do
  257:     POSTPONE (-do) ?do-like ; immediate restrict
  258: 
  259: : U-DO ( compilation -- do-sys ; run-time u1 u2 -- | loop-sys )	\ gforth	u-minus-do
  260:     POSTPONE (u-do) ?do-like ; immediate restrict
  261: 
  262: : FOR ( compilation -- do-sys ; run-time u -- loop-sys )	\ gforth
  263:     POSTPONE (for)
  264:     POSTPONE begin drop do-dest
  265:     ( 0 0 0 >leave ) ; immediate restrict
  266: 
  267: \ LOOP etc. are just like UNTIL
  268: 
  269: : loop-like ( do-sys xt1 xt2 -- )
  270:     >r >r 0 cs-pick swap cell - swap 1 cs-roll r> r> rot do-dest?
  271:     until-like  POSTPONE done  POSTPONE unloop ;
  272: 
  273: : LOOP ( compilation do-sys -- ; run-time loop-sys1 -- | loop-sys2 )	\ core
  274:  ['] (loop) ['] (loop)-lp+!# loop-like ; immediate restrict
  275: 
  276: : +LOOP ( compilation do-sys -- ; run-time loop-sys1 n -- | loop-sys2 )	\ core	plus-loop
  277:  ['] (+loop) ['] (+loop)-lp+!# loop-like ; immediate restrict
  278: 
  279: \ !! should the compiler warn about +DO..-LOOP?
  280: : -LOOP ( compilation do-sys -- ; run-time loop-sys1 u -- | loop-sys2 )	\ gforth	minus-loop
  281:  ['] (-loop) ['] (-loop)-lp+!# loop-like ; immediate restrict
  282: 
  283: \ A symmetric version of "+LOOP". I.e., "-high -low ?DO -inc S+LOOP"
  284: \ will iterate as often as "high low ?DO inc S+LOOP". For positive
  285: \ increments it behaves like "+LOOP". Use S+LOOP instead of +LOOP for
  286: \ negative increments.
  287: : S+LOOP ( compilation do-sys -- ; run-time loop-sys1 n -- | loop-sys2 )	\ gforth	s-plus-loop
  288:  ['] (s+loop) ['] (s+loop)-lp+!# loop-like ; immediate restrict
  289: 
  290: : NEXT ( compilation do-sys -- ; run-time loop-sys1 -- | loop-sys2 ) \ gforth
  291:  ['] (next) ['] (next)-lp+!# loop-like ; immediate restrict
  292: 
  293: \ Structural Conditionals                              12dec92py
  294: 
  295: Defer exit-like ( -- )
  296: ' noop IS exit-like
  297: 
  298: : EXIT ( compilation -- ; run-time nest-sys -- ) \ core
  299:     exit-like
  300:     POSTPONE ;s
  301:     POSTPONE unreachable ; immediate restrict
  302: 
  303: : ?EXIT ( -- ) ( compilation -- ; run-time nest-sys f -- | nest-sys ) \ gforth
  304:      POSTPONE if POSTPONE exit POSTPONE then ; immediate restrict
  305: 

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