Small backtracking

small-backtrack.fs

: ENTER >R ;
: SUCC ' R@ , ' ENTER , ; IMMEDIATE
: FAIL ' R> , ' DROP , ' EXIT , ; IMMEDIATE

: RANGE
  1+ >R 1-
  CREATE
  ' LIT ,
  ,
  POSTPONE BEGIN
  ' 1+ ,
  ' DUP ,
  ' LIT ,
  R> ,
  ' < ,
  POSTPONE WHILE
  POSTPONE SUCC
  POSTPONE REPEAT
  ' DROP ,
  POSTPONE FAIL
  ' EXIT ,
;

1 10 RANGE 1-10

: //2 DUP 2 MOD 0= IF SUCC THEN FAIL ;

: .even1-10 1-10 //2 DUP . ;
.even1-10 \ 2 4 6 8 10

: el  R@ ENTER DROP ;
: .{} CR ." { " DEPTH 0 2DUP = IF 2DROP ELSE DO I PICK . LOOP THEN ." } " ;
: subsets 1
       el 2
       el 3
       el .{} ;

PAGE subsets

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