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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