# Rick van der Zwet
# StudentID: 0433373
# $Id: lecture6.txt 339 2007-11-29 22:01:09Z rick $

All quotes are based on the 8th edition of Concepts of programming
languages from Robert W. Sebesta

*** Chapter 15 Review Questions ***
Problem Set 6,7

6)
Q: What does the following Scheme function do?
(define (y s lis)
    (cond
    ((null? lis) '() )
    ((equal? s (car lis)) lis)
    (else (y s (cdr lis)))
A: It will remove the head of the list till it find s, if none found
   '() is the result

7)
Q: What does the following Scheme function do?
(define (x lis)
    (cond
        ((null? lis) 0)
        ((not (list? (car list)))
            (cond
                ((eq? (car lis) nil) (x (cdr lis)))
                ((else (+ 1 (x (cdr list))))))
        (else (+ (x (car list)) (x cdr lis))))
))
A: It will traverse the lis and count the number of atoms in there


Problem Excercises 4,5,6
4)
Q: Write Scheme function that returns the number of zeros in a given
   simple list of numbers.
A:
(define (x lis)
    (cond
        ((null? lis) 0)
        ((eq? 0 (car lis)) (+ 1 (x (cdr lis)))
        (else (+ 0 (x (cdr lis)))
    )
)

5)
Q: Write a Scheme function that deletes all top-level instances of an
   given atom from a given list
A:
(define (x atom lis)
    (cond
        ((null? lis) '() )
        ((eq? atom lis) (x atom cdr(lis)))
        ((else (cons car(atom) (x atom cdr(lis)))))
    )
)

6)
Q: Write a Scheme function that removes the last element from a given
   list
(define (x list)
    (cond
        ((null? cdr(list) '() ))
        ((else (cons car(list) (x cdr(list)))))
    )
)