[ [] unrot
    swap nested
    ' join nested
    join nested
    ' witheach nested
    swap join
    do ]                  is fs   ( f s --> [ )

 [ 2 * ]                  is f1   (   n --> n )

 [ 2 ** ]                 is f2   (   n --> n )

 [ ' f1 swap fs ]         is fsf1 (   s --> [ )

 [ ' f2 swap fs ]         is fsf2 (   s --> [ )

 ' [ 0 1 2 3 ] fsf1 echo cr
 ' [ 0 1 2 3 ] fsf2 echo cr
 ' [ 2 4 6 8 ] fsf1 echo cr
 ' [ 2 4 6 8 ] fsf2 echo cr

( ... or, using Quackery's partial applicator "witheach",
      which applies the word or nest following it to each
      item in a nest on the top of the stack ...          )

cr

' [ [ 0 1 2 3 ] [ 2 4 6 8 ] ]
  witheach
    [ dup ' [ fsf1 fsf2 ]
      witheach [ do echo cr ] ]