1. what does a macro do?

2. when should you use a macro? 

3. review solution to policy checker macro from homework 5

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4. (this was a question on the C03 final exam)

We have been using cond all semester to write conditionals.  Most
languages include an if-statement for conditionals with only two
cases.  The expression

              (if test then-stmt else-stmt)

should run the test, performing the then-stmt if the test returns
true, otherwise performing the else-stmt.  In this question, we
want to implement such a construct.

4-1. Should if be implemented as a function, as a macro, or as either?
     Justify your answer.

4-2. Implement if.  Your answer should be consistent with your answer
     to 4-1.

4-3. Assume you had augmented your implementation of if with a check
     that the test expression evaluates to a boolean before you execute the
     then or else part (assume that Scheme cond doesn't perform this check
     for you).  Assume you typed the following code into the definitions
     window:

             (define (myfunc x)
	       (if 3 x (+ x 5)))

     Would the error (that the test 3 isn't a boolean) get detected
     when you hit execute, when you enter a call like (myfunc 7)
     from the prompt, neither, or both?  (Answer this based on how you
     implemented if in 4-2.

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5. Write a travel-db macro to convert the trip-planner data into the
   given define-structs

(define-struct flight (from to lasts times))
(define-struct city (name activities))
(define-struct travel-database (cities flights))

(define trip-planner
  (travel-db
   (cities 
    (boston (activities museums dining))
    (austin (activities music outdoors))
    (new-york (activities museums music dining)))
   (flights 
    (boston new-york (duration 50) (times 900 1100 1300 1500 1700))
    (austin boston (duration 200) (times 1100 1430)))))

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6. Write the following function over travel databases

;; city-search : symbol symbol travel-database -> list[symbol] 
;; takes a starting city, an activity and a travel database and returns
;;   a list of city names with the activity and direct flights from the
;;   starting city

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7. Write form and line macros to convert the given tax form format
   into the following define-structs.

(define-struct query-line (number question)) 
(define-struct compute-line (number func line-nums))
(define-struct form (title lines))

(define ez-tax-form
  (form ez-form
        (line 1 "Enter income")
        (line 2 "Enter interest")
        (line 3 "Total income" compute (+ 1 2))
        (line 4 "Enter deductions")
        (line 5 "Gross income" compute (- 3 4))))
        
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8. Write a tax form interpreter for the above form language using the
following helper functions

;; store-line-value : number number -> void
;; stores value (second arg) for line number (first arg) in a database

;; lookup-line-value : number -> number or false
;; takes a line number and retrieves value stored for that number or false
;;    if nothing stored

;; apply : (arg1 ... argn -> ans) list[arg] -> ans
;; sends list of arguments to a function.  For example
;;  (apply + (list 1 2 3)) returns 6