>>331 見た感じ elisp だな．

(defun my-test2 (lst1 lst2)
(my-test2-aux lst1 lst2 nil))
(defun my-test2-aux (lst1 lst2 acc)
(if (null lst1)
(nreverse acc)
(my-test2-aux (cdr lst1) lst2
(my-test2-aux2 (car lst1) lst2 acc))))
(defun my-test2-aux2 (e lst acc)
(if (null lst)
acc
(my-test2-aux2 e (cdr lst) (cons (concat e (car lst)) acc))))

↓どう考えてもこっちのが効率的だとおもうが，なんで再帰でやりたいんだ？？
(defun my-test3 (lst1 lst2)
(let (acc)
(dolist (e1 lst1 (nreverse acc))
(dolist (e2 lst2)
(push (concat e1 e2) acc)))))