> > Write a Function 'total' that takes an orderd list ie.
> > ((itemA quantityA costA)(itemB quantityB costB)....)
> > but returns a list giving the total cost plus the overall cost.
> >
> > Eg:
> >
> > LISP>(total'((book 2 10)(pen 3 2)(notepad 1 12)))
> > ((BOOK 20)(PEN 6)(NOTEPAD 12)(TOTAL 38))
> >
> > Thank you for your time
> >
>
> Here are 3 quite different solutions... one recursive, one iterative,
> and one obscure. I won't do ALL your homework, so you will have to
> figure out yourself how they work, which shouldn't be very hard.
> Disclaimer: I'm quite new to Lisp myself, so there may be better and
> more elegant solutions.
>
> ;;; 1
> (defun total (lst)
> (labels ((total-rec (sublst subtot)
> (if sublst
> (let* ((sub (car sublst))
> (sum (* (cadr sub) (caddr sub))))
> (cons `(,(car sub) ,sum)
> (total-rec (cdr sublst) (+ subtot sum))))
> `((total ,subtot)))))
> (total-rec lst 0)))
>
> ;;; 2
> (defun total (lst)
> (let ((total 0)
> (ret))
> (dolist (elt lst (nreverse (push `(total ,total) ret)))
> (let ((subtotal (* (cadr elt) (caddr elt))))
> (push `(,(car elt) ,subtotal) ret)
> (incf total subtotal)))))
>
> ;;; 3
> (defun total (lst)
> (append
> (mapcar #'(lambda (e) (list (car e) (* (cadr e) (caddr e)))) lst)
> `((total ,(apply #'+ (mapcar #'(lambda (elt) (* (cadr elt) (caddr
> elt))) lst))))))

Let's make it shorter and clearer.

Gauche Scheme and Racket:

(use srfi-1) ;; unzip3 for Gauche
or
(require srfi/1) ;; unzip3 and fold for Racket
(require srfi/8) ;; receive for Racket

(define (total seq)
(receive (items q c) (unzip3 seq)
(define totals (map * q c))
(define grand (fold + 0 totals))
`(,@(map list items totals) (total ,grand))))

(total '((book 2 10) (pen 3 2) (notepad 1 12)))
===>
((book 20) (pen 6) (notepad 12) (total 38))