( During a CASE, the stack grows by 1 at each ENDOF so that
  we can fill all those ENDOF branching addrs. So that we
  know when to stop, we put a 0 on PSP. That's our stopgap. )
: CASE 0 ; IMMEDIATE
: OF
    COMPILE OVER COMPILE =
    [COMPILE] IF COMPILE DROP
; IMMEDIATE
: ENDOF [COMPILE] ELSE ; IMMEDIATE