:: takes an atom, returns a tape representation of its value
++  at-tape
  |=  a=@  ^-  tape
  =|  tick=(list @t)
  =/  n=@  10
  |-
  =/  digit=@  (mod a n)
  ?:  (gte a n)
    $(tick (weld (trip `@t`(add digit 48)) tick), a (div a n))
  (weld (trip `@t`(add digit 48)) tick)