anchor.diff:  \ block for WORD.
   \ This word is part of core ext, but it is very nice for parsing
   \ and used here anyway.
  -: PARSE  \ ( char "ccc<char>" -- c-addr u )                     ( core ext )
  +: PARSE  \ ( char "ccc<char>" -- c-addr u )                     \ word set CORE EXT
       PARSE-POS 0 ROT SWAP
       SRC-SPAN IF
         DO
  
positive.code: : .  ( n -- )
      DUP ABS 0 <# #S ROT SIGN #> TYPE SPACE ;
  
  
  @@
  : ?PAIRS  - IF ABORT" unmatched conditionals" THEN ;
  
negative.code: : 1-  1 - ;
  : INVERT  TRUE XOR ;
  : NEGATE  INVERT 1+ ;
  : DNEGATE  INVERT SWAP NEGATE SWAP OVER 0= - ;      \ word set DOUBLE
  : *  UM* DROP ;
  : S>D  DUP 0< ;
  : ABS  S>D IF NEGATE THEN ;
  : DABS  DUP 0< IF DNEGATE THEN ;                    \ word set DOUBLE
  
  : +!  \  ( n a-addr -- )
      DUP @ ROT + SWAP ! ;
  