;;; $Id: num-of-mod.scm,v 1.3 2006/01/05 22:24:09 leavens Exp $

(module num-of-mod (lib "typedscm.ss" "typedscm")

(provide num-of num-of-slist)

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

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

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

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


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

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

) ;; end module