: BLK! ( -- )
    BLK> @ BLK!* @ EXECUTE
    0 BLKDTY !
;
: FLUSH BLKDTY @ IF BLK! THEN ;
: BLK@ ( n -- )
    DUP BLK> @ = IF DROP EXIT THEN
    FLUSH DUP BLK> ! BLK@* @ EXECUTE ;

: BLK!! 1 BLKDTY ! ;