Exercises

Exercise 1.1.   [*] Locate the Web page for the workshop (see cover). Bookmark it. Copy and paste

Exercise 1.2.   [*] Strings are another important class of data that most programming languages offer. With number→string, you can even convert any number into a string, and with string→number you can convert a string into a number, if the string represents one. Experiment with the two functions in DrScheme’s Interactions window.

Develop the function numbers-to-strings, which consumes a list of numbers and produces a list of strings that represent these numbers. For example, (cons 1 (cons 2 (cons 3 empty))) produces '("1" "2" "3").

Also develop the function strings-to-numbers, which consumes a list of strings and converts them to numbers, if possible. In other words, it uses string→number on each item on the list.

Finally, develop the program strings-to-numbers*. It consumes a list of strings and converts them to numbers. If a string doesn’t represent a number, it drops the item from the list. 

Exercise 1.3.   Networks send requests. Servers process these requests and send responses back.

One way to represent a class of requests is to form a list where each item is a list of two items: a string and a boolean:

;; Request is either 
;; --- empty
;; --- (cons Line Request)
;; Line is (cons String (cons Boolean empty))

Develop the function which-toppings. The function consumes a Request and produces the list of strings that come with true in the given request.