From the J docs: https://www.jsoftware.com/help/dictionary/dx005.htm

  nub=: (i.@# = i.~) # ]
     5!:2 <'nub'
  +-------------------+-+-+
  |+--------+-+------+|#|]|
  ||+--+-+-+|=|+--+-+|| | |
  |||i.|@|#|| ||i.|~||| | |
  ||+--+-+-+| |+--+-+|| | |
  |+--------+-+------+| | |
  +-------------------+-+-+

... so J functions have an array representation, at least.