anchor.diff:  
   \ Global state for all OS services.
   
  -int, rsn
  -
   :, halt,	again, ;,
   :, crash	$C000 #, !,  $C000 #, @, -1 #, xor, $C050 #, !,  $AAAA #, $C0A0 #, !, ;,
   :, 0=		if, 0 #, exit, then, -1 #, ;,
  +
  +\ rsn stores the reason for a service's failure to deliver the expected results.
  +\ Numerous system calls can fail for a number of reasons.  See the errors.fs file
  +\ for a list of reasons and their most common circumstances.
  +int, rsn
   
   \ fillRect draws very simple rectangular patterns on the screen.
   \ This can be used to clear the screen, or to let the user in on the current progress of something.
  
positive.code: \	+6	checksum
  \ The checksum over the whole structure must equal $FFFF.
  \ 
  \ findTag's parameters are as follows:
  \	+0	Return PC
  \	+1	Start address (must be even)
  \	+2	End address (must be even)
  \ Upon success, it returns:
  \	+3	Address of tag
  \	+4	0
  \ Otherwise:
  \	+3	undefined
  \	+4	Reason code (non-zero)
  
  int, fndtagend
  int, fndtagsta
  
negative.code: 	mplsiz @, -/node and, -/node +, mplsta @, 2 #, +, !,  ;,
  
  \ getmem allocates a block of memory from a formatted memory pool.  The mplsta
  \ variable must point to the pool to allocate from.  memsiz holds the request
  \ size.
  \ 
  \ If the request can be satisfied, memptr holds the address of the allocated
  \ block of memory, and rsn is zero.  Otherwise, memptr is undefined, and rsn
  \ indicates why the request failed.
  
  int, p
  int, q
  