(use tree-rewrite)

(define rule-toc
  `( 
    ( (M section $level $title) => (li $title) )
    ))



(define test
  `(M body

      (page-title)

       (section 2 "Abstract")

       (p "This is the abstract")
       
       (p "This is the second paragraph.")
       
       (section 2 "Results")
       
       (p "This is the next section")
       
       (section 2 "Discussion") 

       (p "This is the final section. ")
       (p "This is a paragraph. ")
       (p "This is another paragraph. ")
       
       ))

(print ((rewrite-fold-tree-partial rule-toc cons '()) test ))