! for a nested sequence, all elements are of type sequence
! we can't subclass array, as it's final :(

TUPLE: wrapped-array { underlying array read-only } ;
TUPLE: nested-array < wrapped-array ;
INSTANCE: nested-array nested-sequence

! here: code delegating nested arrays

ERROR: not-all-sequences ;

: >nested-array ( seq -- nested-array )
  dup [ sequence? ] all? [ not-all-sequences ] unless
  >array nested-array boa ;