anchor.diff:  \ current top of the return stack.  R@ is also known as I,
   \ for applications working with DO...LOOP constructs.
   
  -tcode R>	\ TODO test
  +tcode R>
   	0 rsp x8 ld,
   	8 rsp rsp addi,
   	-8 dsp dsp addi,
  
positive.code: \ to a corresponding FOR-loop's entry is NOT taken.  It
  \ is compiled by NEXT.
  \ 
  \ (dofor) moves a count to the return stack, less one,
  \ as per the semantics for a FOR-loop.  It is compiled
  \ by FOR.
  tcode ?next
  	0 rsp x9 ld,
  	-1 x9 x9 addi,
  
negative.code: 	next,
  tend-code
  
  tcode >R
  	0 dsp x8 ld,
  	8 dsp dsp addi,
  	-8 rsp rsp addi,
  