(TML)

let cons x y = x.y ;;

letrec concat x = (null x => [] | (hd x)@(concat (tl x)));;

letrec perms n =
  if n=0 then [[]] else
     insert n (perms (n-1)) where
              insert n x = concat (map (put n) x) whererec
                     put n x = if null x then [[n]]
                                  else (n.x).(map (cons (hd x))
                                                  (put n (tl x))) ;;

letrec p x = if null x then [[]] else f x 
  whererec f (a.y) = (map (cons a) (p y)) @ g(y @ [a])
       and g y = if x=y then [] else f y ;;