(defun my-depth-first-graph-search (frontier neighbors goalp)
  "Perform depth-first search (DFS) on a graph.

All arguments are like those for `my-graph-search', which see."
  (let ((lifo (lambda (frontier paths) (nconc paths frontier))))
    (my-graph-search frontier neighbors goalp lifo)))

(defalias 'my-dfs-graph-search #'my-depth-first-graph-search)

(let ((graph '((a b c d)
               (b a e i)
               (c a f)
               (d a g l)
               (e b i j)
               (f c)
               (g d k l)
               (i b e)
               (j e)
               (k g)
               (l d g)))
      (my-graph-search-debug t))
  (princ (format "Solution: %s\n"
                 (my-bfs-graph-search
                  '((a))
                  (lambda (path) (alist-get (car path) graph))
                  (lambda (path) (eq (car path) 'f))))))