anchor.diff:      \ skip all characters satisfying xt ( c -- f )
       >r
       BEGIN
  -    over c@ r@ execute
  -    over 0<> and
  +        over c@ r@ execute
  +        overand
       WHILE
  -	1/string
  +        1/string
       REPEAT
       r> drop ;
   
  
positive.code:     begin
          2dupxor
      while
          dup c@ c,
          1+
      repeat
      2drop
      align
  
negative.code: \ From Forth200x - public domain
  
  : isspace? ( c -- f )
      h# 21 u< ;
  
  : isnotspace? ( c -- f )
      isspace? 0= ;
  