{def powerset

{def powerset.r
 {lambda {:ary :ps :i}
  {if {= :i {A.length :ary}}
   then :ps
   else {powerset.r :ary
                    {powerset.rr :ary :ps {A.length :ps} :i 0}
                    {+ :i 1}} }}}

{def powerset.rr
 {lambda {:ary :ps :len :i :j}
  {if {= :j :len}
   then :ps
   else {powerset.rr :ary
                     {A.addlast! {A.concat {A.get :j :ps}
                                           {A.new {A.get :i :ary}}}
                                 :ps}
                     :len
                     :i
                     {+ :j 1}} }}}

 {lambda {:ary}
  {A.new {powerset.r :ary {A.new {A.new}} 0}}}}

-> powerset

{powerset {A.new 1 2 3 4}}
-> [[],[1],[2],[1,2],[3],[1,3],[2,3],[1,2,3],[4],[1,4],[2,4],[1,2,4],[3,4],[1,3,4],[2,3,4],[1,2,3,4]]]