Lab 6: Chatting about Design

Make sure you follow The Style we use for the {B,I,A}SL{,+} languages in this class.

Make sure you save and submit your definitions, we will be extending this program in future labs. Choose the initial Head and Hands, and get started!

Messages

Recall add-message : String String Image -> Image from the second assignment. The message add-message adds to the history has two parts: the name and the content.

Ex 1: Using the given structure definition msg, design a data definition and template for Messages.

(define-struct msg (name content))

; A Message is a ______.

(define (message-template msg) _____)

(define msg1 (make-msg "DVH" "Hello, world!"))

(define msg2 (make-msg "Nick & Sam" "Help! What should we do?!"))

(define msg3 (make-msg "DVH" "Do not be afraid; do not be discouraged, for the Design Recipe will be with you wherever you go."))

Ex 2: Give three data examples of Messages (other than the three we provided).

Ex 3: Design the function message->image that returns an image representation of the given Message. The name and content of the Message must have different colors. Be sure to write tests for your three Message examples before implementing the function.

Ex 4: Change the color of the font you used for the message name. Make sure you update your tests as well.

Ex 5: Change the size of the font you used for the message content. Make sure you update your tests as well.

Ex 6: If you haven’t by now, define and name all constants used in the function message->image for easy customization.

Add-Message Redux

Swap Head and Hands!

Add the following snippet to your definitions window.

; A History is an Image.

(define empty-history empty-image)

(define hist1 (add-message msg1 empty-history))

(define hist2 (add-message msg2 hist1))

(define hist3 (add-message msg3 hist2))

Ex 7: What kind of data is a History (e.g. enumeration, atomic, composite, recursive)? Answer in a comment in the definitions window.

Ex 8: Design the function add-message that adds the given Message below the given History, returning a new History. The text of the messages should be aligned on the left. Make sure you write your tests before you implement the function.

Writing Messages

We want to be able to send messages, but first we need to know how to write messages!

Take a look at the following data definition, then copy it into your definitions window.

; A Natural is a non-negative integer.

(define-struct textbox (content cursor))

; A Textbox is a (make-textbox String Natural)

; Interp: a textbox (make-textbox str n) has its cursor immediately before the

; Nth character of STR. The cursor's value must never exceed the length of

; the string.

(define tb0 (make-textbox "foo " 0))

(define tb1 (make-textbox "foo " 1))

(define tb2 (make-textbox "foo " 2))

(define tb3 (make-textbox "foo " 3))

(define tb4 (make-textbox "foo " 4))

Ex 9: Design the function before-cursor : Textbox -> String which returns the string content of the given Textbox that comes before the cursor.

Ex 10: Design the function after-cursor : Textbox -> String which returns the string content of the given Textbox that comes after the cursor.

Ex 11: Implement the function textbox->image that creates an image representation of a Textbox. The content can be any size or color you want, and you should draw the cursor as a tall, skinny rectangle between the content that comes before and after the cursor.

; textbox->image : Textbox -> Image

; Create an image representation of the given Textbox.

(define TBCTNT-COLOR "orange")

(define TBCTNT-SIZE 16)

(define TBCURS-COLOR "red")

(define TBCURS-HEIGHT 20)

(define TBCURS-WIDTH 2)

(define TBCURS (rectangle TBCURS-WIDTH TBCURS-HEIGHT 'solid TBCURS-COLOR))

(define (textbox->image tb) empty-image) ; <- stub

(check-expect (textbox->image tb0) ...) ; => |foo

(check-expect (textbox->image tb1) ...) ; => f|oo

(check-expect (textbox->image tb2) ...) ; => fo|o

(check-expect (textbox->image tb3) ...) ; => foo|

(check-expect (textbox->image tb4) ...) ; => foo |