Annotation of gforth/compat/loops.fs, revision 1.2
1.1 anton 1: \ +DO, -DO...-LOOP and friends
2:
3: \ This file is in the public domain. NO WARRANTY.
4:
5: \ Hmm, this would be a good application for ]] ... [[
6:
7: : +DO ( compile-time: -- do-sys; run-time: n1 n2 -- )
8: POSTPONE over POSTPONE min POSTPONE ?do ; immediate
9:
10: : umin ( u1 u2 -- u )
11: 2dup u>
12: IF
13: swap
1.2 ! anton 14: THEN
1.1 anton 15: drop ;
16:
17: : U+DO ( compile-time: -- do-sys; run-time: u1 u2 -- )
18: POSTPONE over POSTPONE umin POSTPONE ?do ; immediate
19:
20: \ -DO...-LOOP
21:
22: \ You have to use the -LOOP implemented below with -DO or U-DO, you
23: \ cannot use it with ?DO
24:
25: \ The implementation is a little more complicated. Basically, we
26: \ create an IF DO ... +LOOP THEN structure. The DO..+LOOP does not
27: \ exhibit the anomaly of ?DO...+LOOP; the IF..THEN is needed to
28: \ correct for DO's at-least-once semantics. The parameters are
29: \ conditioned a bit such that the result is as expected.
30:
31: \ I define a '-do-sys' (whose implementation is 'orig do-sys'). Like
32: \ ANS Forth loop structures, this implementation of -DO..-LOOP
33: \ cannot be mixed with any other structures.
34:
35: \ unlike Gforth's -LOOP, this implementation cannot handle all
36: \ unsigned increments, only positive integers
37: : -LOOP ( compilation -do-sys -- ; run-time loop-sys1 +n -- | loop-sys2 )
38: POSTPONE negate POSTPONE +loop
39: POSTPONE else POSTPONE 2drop POSTPONE then ; immediate
40:
41: : -DO ( compilation -- -do-sys ; run-time n1 n2 -- | loop-sys )
42: POSTPONE 2dup POSTPONE < POSTPONE if
43: POSTPONE swap POSTPONE 1+ POSTPONE swap POSTPONE do ; immediate
44:
45: : U-DO ( compilation -- -do-sys ; run-time u1 u2 -- | loop-sys )
46: POSTPONE 2dup POSTPONE u< POSTPONE if
47: POSTPONE swap POSTPONE 1+ POSTPONE swap POSTPONE do ; immediate
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