~~~
:double:var (:nns-)
  d:create swap , , ;

:double:fetch (:a-nn)
  fetch-next swap fetch ;

:double:store (:nna-)
  &swap dip store-next store ;

:double:const (:nns-)
  double:var &double:fetch does ;

:double:swap (:nnmm-mmnn)
  rot push rot pop ;

:double:dip (:mnq-mn) rot rot push push call pop pop ;
:double:sip (:mnq-mn) &dup-pair dip double:dip ;
~~~