;; The first three lines of this file were inserted by DrRacket. They record metadata
;; about the language level of this file in a form that our tools can easily process.
#reader(lib "htdp-beginner-reader.ss" "lang")((modname lect07) (read-case-sensitive #t) (teachpacks ()) (htdp-settings #(#t constructor repeating-decimal #f #t none #f ())))
#|  calculate ebay fees:
   When you sell something on ebay, you are charged:
    - a listing fee, $0.30
    - a gallery-plus fee, $0.35, *if* you used the gallery.
    - a final-value fee:
       10% of up to the first $100;
        5% of up to the next $900;
        2% thereafter.

     [N.B. sometime in 2013, ebay changed this to just 10% of price+shipping.]

  Follow the design recipe:
    4. write test cases
    5  (a-d): header, purpose, contract/type, stub-return
    7. complete the body
    8. run tests

  [...10min of class work here...]

  How to do if-else-if?  use `cond`.
  Pay close attention to the parens.
  Syntax:
    (cond [q1 a1]
          [q2 a2]
          ...
          [qn an])
     where each q1,..,qn and a1,..,an are expressions,
     possibly w/ their own parens.

    Note that racket treats all types of parens the same, so long as they match:
    {define n 5} is entirely legal (if non-standard).
|#


(define FLAT-INSERT-FEE 0.30)
(define GALLERY-FEE 0.35)
(define REVOKE-PENALTY 5.00)





#|  Now, last 5min:
  - Modify the problem: the function can be given
    a sale-price, *or*
    the symbol 'unsold (no fees at all), or
    the symbol 'canceled ($5 plus insertion fee and gallery fee)

  - These inputs are *union* types:
     [0,100) u [100,1000) u [1000,+infty) 
     {'unsold} u {'canceled} u real

 Design recipe update:
  6a. If handling union data, use a *cond*, with one branch for each type.
 |#