;;; sample.scm - first Scheme example for CS 313
;;;
;;; Daniel Scharstein

; This file implements some of the functions discussed in class.  To
; run it, start Scheme by typing "scheme" (in this directory).  Then
; load this file by typing (load "sample").  This executes all the
; code in this file:

; 1 ]=> (load "sample")
;
; ;Loading "sample.scm"
;
; L = ((a b) ((c)) (d (e)))
; (mylength L) = 3
; (count-atoms L) = 5
; (myreverse L) = ((d (e)) ((c)) (a b))
; (fact 7) = 5040
;
;  -- done



;; handy reload function
(define (r)
  (load "sample"))


;; return length of list x
(define (mylength x)
  (if (null? x)
      0
      (+ 1 (mylength (cdr x)))))

;; return whether x is an atom
(define (atom? x)
  (not (pair? x)))

;; return number of atoms in x
(define (count-atoms x)
  (cond ((null? x) 0)
	((atom? x) 1)
	(else (+ (count-atoms (car x))
		 (count-atoms (cdr x))))))

;; return factorial of n
(define (fact n)
  (if (<= n 1)
      1
      (* n (fact (- n 1)))))

;; return new list formed by appending x and y
(define (myappend x y)
  (if (null? x)
      y
      (cons (car x)
	    (myappend (cdr x) y))))

;; return reverse of list x (inefficient!)
(define (myreverse x)
  (if (null? x)
      ()
      (myappend
       (myreverse (cdr x))
       (list (car x)))))
  
;;; testing:

(newline) (newline)

(define L '((a b) ((c)) (d (e))))

(display "L = ") (display L) (newline)

(display "(mylength L) = ") (display (mylength L)) (newline)

(display "(count-atoms L) = ") (display (count-atoms L)) (newline)

(display "(myreverse L) = ") (display (myreverse L)) (newline)

(display "(fact 7) = ") (display (fact 7)) (newline)

(newline)
#t  ;; to avoid 'unspecified return value' message