Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.lisp > #60184

Re: Lisp Function Problem

Cross-posted to 2 groups.

Show all headers | View raw

> > 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))))))

Gauche Scheme

(define (proc stuff)
  (let* ((items (map car stuff))
         (costs (map (~>> cdr (apply *)) stuff))
         (total (fold + 0 costs)))
    (append (map list items costs)
            `((total ,total)))))

Given:

(define-syntax ->>
  (syntax-rules ()
    [(_ x)  x]
    [(_ x (y ...) z ...)
     (->> (y ... x) z ...)]
    [(_ x y z ...)
     (->> (y x) z ...)]))

(define-syntax ~>>
  (syntax-rules ()
    [(_ (func0 a ...) func ...)
     (lambda xs (->> (apply func0 a ... xs) func ...))]
    [(_ func0 func ...)
     (lambda xs (->> (apply func0 xs) func ...))]))

Back to comp.lang.lisp | Previous | Next — Next in thread | Find similar

Thread

Re: Lisp Function Problem "B. Pym" <Nobody447095@here-nor-there.org> - 2024-09-26 12:20 +0000
  Re: Lisp Function Problem "B. Pym" <Nobody447095@here-nor-there.org> - 2025-08-07 23:30 +0000

csiph-web