My assignment looks like this: Suppose you are writing a Scheme program for a grocery store that will calculate the total price of a customer’s items, represented as a list. Your partner suggests writing a series of Scheme forms like (define item price) then recursively going through the list using those defines to calculate the sum. I wrote the code, but when I call the function, I get an error.
#lang scheme
(define milk 2.99)
(define chicken 7.99)
(define carrots 1.99)
(define add-cart
(lambda(x)
(if (empty? x) 0
(+ (car x) (add-cart (cdr x))))))
(add-cart '(milk chicken carrots))
Error:
+: contract violation
expected: number?
given: carrots
I am still new too scheme just got introduced to it last week, but it is really frustrating. What am I doing wrong? Maybe you have some advice? I would be grateful for any hint.
