[ over not
    over and
    unrot not
    and or ]                  is xor       (                     a b --> a^b           )

  [ 2dup and
    dip xor ]                 is halfadder (                     a b --> s c           )

  [ halfadder
    dip halfadder or ]        is fulladder (                   a b c --> s c           )

  [ 4 pack reverse unpack
    4 times [ temp put ]
    4 pack reverse
    0 swap witheach
      [ temp take fulladder ]
    5 pack reverse unpack ]   is 4bitadder ( b3 b2 b1 b0 a3 a2 a1 a0 --> c s3 s2 s1 s0 )

    say "1100 + 1100 = "
    1 1 0 0  1 1 0 0 4bitadder
    5 pack witheach echo
    cr
    say "1100 + 1101 = "
    1 1 0 0  1 1 0 1 4bitadder
    5 pack witheach echo
    cr
    say "1100 + 1110 = "
    1 1 0 0  1 1 1 0 4bitadder
    5 pack witheach echo
    cr
    say "1100 + 1111 = "
    1 1 0 0  1 1 1 1 4bitadder
    5 pack witheach echo
    cr
    say "1101 + 0000 = "
    1 1 0 1  0 0 0 0 4bitadder
    5 pack witheach echo
    cr
    say "1101 + 0001 = "
    1 1 0 1  0 0 0 1 4bitadder
    5 pack witheach echo
    cr
    say "1101 + 0010 = "
    1 1 0 1  0 0 1 0 4bitadder
    5 pack witheach echo
    cr
    say "1101 + 0011 = "
    1 1 0 1  0 0 1 1 4bitadder
    5 pack witheach echo
    cr