;;; $Id: count-sym-exp-mod.scm,v 1.1 2006/01/04 07:00:55 leavens Exp $

(module count-sym-exp-mod (lib "typedscm.ss" "typedscm")

  (provide count-sym-exp count-slist)

  ;; Examples:
  ;; (count-sym-exp 'a (parse-sym-exp 'a)) ==> 1
  ;; (count-sym-exp 'a (parse-sym-exp 'b)) ==> 0
  ;; (count-sym-exp 'x (parse-sym-exp '(x y (x)))) ==> 2
  ;; (count-sym-exp 'x (parse-sym-exp '(y (x)))) ==> 1

  ;; Grammar:
  ;; <sym-exp>::= <symbol> | <s-list>
  ;; <s-list> ::= ( {<sym-exp>}* )

  (require (lib "sym-exp-cooked.scm" "lib342"))

  (deftype count-sym-exp (-> (symbol sym-exp) number))
  (define count-sym-exp
    (lambda (sym symexp)
      (if (sym-exp-symbol? symexp)
          (if (eq? sym (sym-exp->symbol symexp))
              1
              0)
          (count-slist sym (sym-exp->s-list symexp)))))


  ;; Examples:
  ;; (count-slist 'x (parse-s-list '())) ==> 0
  ;; (count-slist 'x (parse-s-list '(x y (x)))) ==> 2
  ;; (count-slist 'x (parse-s-list '(y (x)))) ==> 1

  (deftype count-slist
    (-> (symbol (list-of sym-exp)) number))
  (define count-slist
    (lambda (sym slist)
      (if (null? slist)
          0
          (+ (count-sym-exp sym (car slist))
             (count-slist sym (cdr slist))))))

  ) ;; end module