(use tree-rewrite)

(include "arith.scm")

(define (list->seq lst)
  (if (null? lst) '(seq-empty)
      `(seq ,(car lst) ,(list->seq (cdr lst)))))

;; Extract the nth element from a sequence of elements 
;; nth(0,(t,_)) -> somestr(t)
;; nth(n,(_,l)) when n > 0 -> nth(n - 1,l)

(define rule-seq
  `( 
    ( (M nth (zero) (seq $h $t)) => $h )
    ( (M nth (succ $n) (seq $h $t)) => (M nth $n $t) )
    
    ,@rule-arith
    ))


(define term `(M nth ,(make-numeral 2) ,(list->seq '(a b c d))))
(pp term)
(print (reduce term rule-seq))