Annotation of gforth/kernel/cond.fs, revision 1.8
1.1 anton 1: \ Structural Conditionals 12dec92py
2:
1.4 anton 3: \ Copyright (C) 1995,1996,1997 Free Software Foundation, Inc.
1.1 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
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
1.6 jwilke 51: [IFUNDEF] defstart
52: 0 constant defstart \ usally defined in comp.fs
53: [THEN]
1.1 anton 54: 1 constant live-orig
55: 2 constant dead-orig
56: 3 constant dest \ the loopback branch is always assumed live
57: 4 constant do-dest
58: 5 constant scopestart
59:
60: : def? ( n -- )
61: defstart <> abort" unstructured " ;
62:
63: : orig? ( n -- )
64: dup live-orig <> swap dead-orig <> and abort" expected orig " ;
65:
66: : dest? ( n -- )
67: dest <> abort" expected dest " ;
68:
69: : do-dest? ( n -- )
70: do-dest <> abort" expected do-dest " ;
71:
72: : scope? ( n -- )
73: scopestart <> abort" expected scope " ;
74:
75: : non-orig? ( n -- )
76: dest scopestart 1+ within 0= abort" expected dest, do-dest or scope" ;
77:
78: : cs-item? ( n -- )
79: live-orig scopestart 1+ within 0= abort" expected control flow stack item" ;
80:
81: 3 constant cs-item-size
82:
1.7 crook 83: : CS-PICK ( ... u -- ... destu ) \ tools-ext c-s-pick
1.1 anton 84: 1+ cs-item-size * 1- >r
85: r@ pick r@ pick r@ pick
86: rdrop
87: dup non-orig? ;
88:
1.7 crook 89: : CS-ROLL ( destu/origu .. dest0/orig0 u -- .. dest0/orig0 destu/origu ) \ tools-ext c-s-roll
1.1 anton 90: 1+ cs-item-size * 1- >r
91: r@ roll r@ roll r@ roll
92: rdrop
93: dup cs-item? ;
94:
95: : cs-push-part ( -- list addr )
1.3 pazsan 96: locals-list @ here ;
1.1 anton 97:
98: : cs-push-orig ( -- orig )
99: cs-push-part dead-code @
100: if
101: dead-orig
102: else
103: live-orig
104: then ;
105:
106: \ Structural Conditionals 12dec92py
107:
108: : ?struc ( flag -- ) abort" unstructured " ;
109: : sys? ( sys -- ) dup 0= ?struc ;
110: : >mark ( -- orig )
111: cs-push-orig 0 , ;
112: : >resolve ( addr -- ) here over - swap ! ;
113: : <resolve ( addr -- ) here - , ;
114:
115: : BUT
116: 1 cs-roll ; immediate restrict
117: : YET
118: 0 cs-pick ; immediate restrict
119:
120: \ Structural Conditionals 12dec92py
121:
122: : AHEAD ( compilation -- orig ; run-time -- ) \ tools-ext
123: POSTPONE branch >mark POSTPONE unreachable ; immediate restrict
124:
125: : IF ( compilation -- orig ; run-time f -- ) \ core
126: POSTPONE ?branch >mark ; immediate restrict
127:
128: : ?DUP-IF ( compilation -- orig ; run-time n -- n| ) \ gforth question-dupe-if
1.5 crook 129: \G This is the preferred alternative to the idiom "@code{?DUP IF}", since it can be
1.1 anton 130: \G better handled by tools like stack checkers. Besides, it's faster.
131: POSTPONE ?dup-?branch >mark ; immediate restrict
132:
133: : ?DUP-0=-IF ( compilation -- orig ; run-time n -- n| ) \ gforth question-dupe-zero-equals-if
134: POSTPONE ?dup-0=-?branch >mark ; immediate restrict
135:
136: Defer then-like ( orig -- )
137: : cs>addr ( orig/dest -- ) drop >resolve drop ;
138: ' cs>addr IS then-like
139:
140: : THEN ( compilation orig -- ; run-time -- ) \ core
141: dup orig? then-like ; immediate restrict
142:
143: ' THEN alias ENDIF ( compilation orig -- ; run-time -- ) \ gforth
144: immediate restrict
145: \ Same as "THEN". This is what you use if your program will be seen by
146: \ people who have not been brought up with Forth (or who have been
147: \ brought up with fig-Forth).
148:
149: : ELSE ( compilation orig1 -- orig2 ; run-time f -- ) \ core
150: POSTPONE ahead
151: 1 cs-roll
152: POSTPONE then ; immediate restrict
153:
154: Defer begin-like ( -- )
155: ' noop IS begin-like
156:
157: : BEGIN ( compilation -- dest ; run-time -- ) \ core
158: begin-like cs-push-part dest ; immediate restrict
159:
160: Defer again-like ( dest -- addr )
161: ' nip IS again-like
162:
163: : AGAIN ( compilation dest -- ; run-time -- ) \ core-ext
164: dest? again-like POSTPONE branch <resolve ; immediate restrict
165:
1.8 ! anton 166: Defer until-like ( list addr xt1 xt2 -- )
! 167: :noname ( list addr xt1 xt2 -- )
! 168: drop compile, <resolve drop ;
! 169: IS until-like
1.1 anton 170:
171: : UNTIL ( compilation dest -- ; run-time f -- ) \ core
172: dest? ['] ?branch ['] ?branch-lp+!# until-like ; immediate restrict
173:
174: : WHILE ( compilation dest -- orig dest ; run-time f -- ) \ core
175: POSTPONE if
176: 1 cs-roll ; immediate restrict
177:
178: : REPEAT ( compilation orig dest -- ; run-time -- ) \ core
179: POSTPONE again
180: POSTPONE then ; immediate restrict
181:
182: \ counted loops
183:
184: \ leave poses a little problem here
185: \ we have to store more than just the address of the branch, so the
186: \ traditional linked list approach is no longer viable.
187: \ This is solved by storing the information about the leavings in a
188: \ special stack.
189:
190: \ !! remove the fixed size limit. 'Tis not hard.
191: 20 constant leave-stack-size
192: create leave-stack 60 cells allot
193: Avariable leave-sp leave-stack 3 cells + leave-sp !
194:
195: : clear-leave-stack ( -- )
196: leave-stack leave-sp ! ;
197:
198: \ : leave-empty? ( -- f )
199: \ leave-sp @ leave-stack = ;
200:
201: : >leave ( orig -- )
202: \ push on leave-stack
203: leave-sp @
204: dup [ leave-stack 60 cells + ] Aliteral
205: >= abort" leave-stack full"
206: tuck ! cell+
207: tuck ! cell+
208: tuck ! cell+
209: leave-sp ! ;
210:
211: : leave> ( -- orig )
212: \ pop from leave-stack
213: leave-sp @
214: dup leave-stack <= IF
215: drop 0 0 0 EXIT THEN
216: cell - dup @ swap
217: cell - dup @ swap
218: cell - dup @ swap
219: leave-sp ! ;
220:
221: : DONE ( compilation orig -- ; run-time -- ) \ gforth
222: \ !! the original done had ( addr -- )
223: drop >r drop
224: begin
225: leave>
226: over r@ u>=
227: while
228: POSTPONE then
229: repeat
230: >leave rdrop ; immediate restrict
231:
232: : LEAVE ( compilation -- ; run-time loop-sys -- ) \ core
233: POSTPONE ahead
234: >leave ; immediate restrict
235:
236: : ?LEAVE ( compilation -- ; run-time f | f loop-sys -- ) \ gforth question-leave
237: POSTPONE 0= POSTPONE if
238: >leave ; immediate restrict
239:
240: : DO ( compilation -- do-sys ; run-time w1 w2 -- loop-sys ) \ core
241: POSTPONE (do)
242: POSTPONE begin drop do-dest
243: ( 0 0 0 >leave ) ; immediate restrict
244:
245: : ?do-like ( -- do-sys )
246: ( 0 0 0 >leave )
247: >mark >leave
248: POSTPONE begin drop do-dest ;
249:
250: : ?DO ( compilation -- do-sys ; run-time w1 w2 -- | loop-sys ) \ core-ext question-do
251: POSTPONE (?do) ?do-like ; immediate restrict
252:
253: : +DO ( compilation -- do-sys ; run-time n1 n2 -- | loop-sys ) \ gforth plus-do
254: POSTPONE (+do) ?do-like ; immediate restrict
255:
256: : U+DO ( compilation -- do-sys ; run-time u1 u2 -- | loop-sys ) \ gforth u-plus-do
257: POSTPONE (u+do) ?do-like ; immediate restrict
258:
259: : -DO ( compilation -- do-sys ; run-time n1 n2 -- | loop-sys ) \ gforth minus-do
260: POSTPONE (-do) ?do-like ; immediate restrict
261:
262: : U-DO ( compilation -- do-sys ; run-time u1 u2 -- | loop-sys ) \ gforth u-minus-do
263: POSTPONE (u-do) ?do-like ; immediate restrict
264:
265: : FOR ( compilation -- do-sys ; run-time u -- loop-sys ) \ gforth
266: POSTPONE (for)
267: POSTPONE begin drop do-dest
268: ( 0 0 0 >leave ) ; immediate restrict
269:
270: \ LOOP etc. are just like UNTIL
271:
272: : loop-like ( do-sys xt1 xt2 -- )
273: >r >r 0 cs-pick swap cell - swap 1 cs-roll r> r> rot do-dest?
274: until-like POSTPONE done POSTPONE unloop ;
275:
276: : LOOP ( compilation do-sys -- ; run-time loop-sys1 -- | loop-sys2 ) \ core
277: ['] (loop) ['] (loop)-lp+!# loop-like ; immediate restrict
278:
279: : +LOOP ( compilation do-sys -- ; run-time loop-sys1 n -- | loop-sys2 ) \ core plus-loop
280: ['] (+loop) ['] (+loop)-lp+!# loop-like ; immediate restrict
281:
282: \ !! should the compiler warn about +DO..-LOOP?
283: : -LOOP ( compilation do-sys -- ; run-time loop-sys1 u -- | loop-sys2 ) \ gforth minus-loop
284: ['] (-loop) ['] (-loop)-lp+!# loop-like ; immediate restrict
285:
286: \ A symmetric version of "+LOOP". I.e., "-high -low ?DO -inc S+LOOP"
287: \ will iterate as often as "high low ?DO inc S+LOOP". For positive
288: \ increments it behaves like "+LOOP". Use S+LOOP instead of +LOOP for
289: \ negative increments.
290: : S+LOOP ( compilation do-sys -- ; run-time loop-sys1 n -- | loop-sys2 ) \ gforth s-plus-loop
291: ['] (s+loop) ['] (s+loop)-lp+!# loop-like ; immediate restrict
292:
293: : NEXT ( compilation do-sys -- ; run-time loop-sys1 -- | loop-sys2 ) \ gforth
294: ['] (next) ['] (next)-lp+!# loop-like ; immediate restrict
295:
296: \ Structural Conditionals 12dec92py
297:
298: Defer exit-like ( -- )
299: ' noop IS exit-like
300:
301: : EXIT ( compilation -- ; run-time nest-sys -- ) \ core
1.5 crook 302: \G Return to the calling definition; usually used as a way of
303: \G forcing an early return from a definition. Before
304: \G @code{EXIT}ing you must clean up the return stack and
305: \G @code{UNLOOP} any outstanding @code{?DO}...@code{LOOP}s.
1.1 anton 306: exit-like
307: POSTPONE ;s
308: POSTPONE unreachable ; immediate restrict
309:
310: : ?EXIT ( -- ) ( compilation -- ; run-time nest-sys f -- | nest-sys ) \ gforth
311: POSTPONE if POSTPONE exit POSTPONE then ; immediate restrict
312:
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