{def inject
 {lambda {:x :a}
  {if {A.empty? :a}
   then {A.new {A.new :x}}
   else {let { {:c {{lambda {:a :b} {A.cons {A.first :a} :b}} :a}}
               {:d {inject :x {A.rest :a}}}
               {:e {A.cons :x :a}}
             } {A.cons :e {A.map :c :d}}}}}}
-> inject

{def permut
 {lambda {:a}
  {if {A.empty? :a}
   then {A.new :a}
   else {let { {:c {{lambda {:a :b} {inject {A.first :a} :b}} :a}}
               {:d {permut {A.rest :a}}}
             } {A.reduce A.concat {A.map :c :d}}}}}}
-> permut

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

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