Problem Set 4: Several text editors

Submit this assignment to ps4 on Handin.

Important: Whenever you write a function in this class, follow the design recipe. You will be graded accordingly.

1 Structures

Problem 2. According to WesPortal, an address has a first address line, a second address line, a city, a state and a zip code. For example, the Department of Mathematics and Computer Science has first address line "265 Church Street", second address line "Science Tower 655", city "Middletown", state "CT" and zip code "06459". We will store zip codes as Strings in order to preserve leading zeroes.

Create a structure definition and a data definition for an address. Call the structure address with fields line1, line2, city, state and zip.

Problem 3. Write the template for processing an address. Call the template process-address.

Problem 4. Design a function called connecticut? which, given an address, determines if it is in Connecticut. A Connecticut address has a zip code between 06000 and 06999. The function string->number may be useful.

Problem 5. Design a function called format-address which, given an address, produces a string that you might write on a letter to that address. In other words, this function should consume an address data structure and produce a formatted string.

Note that line breaks are optional in this problem. If you do want to include them, line breaks are encoded as "\n". DrRacket does not display line breaks in strings as actual line breaks. If you’d like to see the line breaks displayed as actual line breaks, try composing format-address with text in the Interactions Window.

Problem 6. Design a function called smaller-zip which, given two addresses, produces the address with the smaller zip code. (It doesn’t matter which address is returned if their zip codes are equal.)

2 Key events

Similar to MouseEvent, KeyEvent is an enumeration of all the possible keyboard events, represented as Strings, to which big-bang can respond. Each keyboard event is represented by a String: for example, the KeyEvent "q" stands for the key q being pressed.

KeyEvent is a very long enumeration and it is not practical to work with it in its entirety most of the time. When we write function templates that process KeyEvents, we typically use cond clauses to distinguish KeyEvents of interest and use else to handle the remaining KeyEvents.

Problem 7. Design a function draw which takes a string as input and draws it as an image. The text function will be useful. Make sure to place the text on a larger background image, like you did with the date in Problem Set 1: Painting in DrRacket.

Next, copy the following key handler and big-bang call into your Definitions Window and click run.

; key->string : String KeyEvent -> String

; ignores the input String and outputs the KeyEvent as a String

(define (key->string s ke) ke)

(check-expect (key->string "q" "w") "w")

(check-expect (key->string "q" "left") "left")

; a World is a String

(big-bang ""

[to-draw draw]

[on-key key->string])

Try typing various keys, including the arrow keys and the shift keys. Notice which keys are represented as strings with length one, and which ones aren’t. When you are finished, comment out the big-bang call (the last three lines above).

Problem 8. 1String is the enumeration of all of the possible strings of length one. Design a function key->1string which takes a 1String and a KeyEvent and returns the KeyEvent as a 1String if it has length one. If the KeyEvent doesn’t have length one, the input 1String is returned instead. Hint: Your conditional should have two clauses, one of which is an else clause.

Try out key->1string by creating a big-bang animation with key->1string as the key handler and with draw. Run the animation, play with it, and comment it out when you are done.

Problem 9. Design a function lengthen which takes a String and a KeyEvent and uses the KeyEvent to somehow lengthen the input String.

Try out lengthen by creating a big-bang animation with lengthen as the key handler and with draw. Run the animation, play with it, and comment it out when you are done.

Problem 10. Design a function lengthen-with-reset which behaves like lengthen but with the exception that pressing the space bar causes the current string to become empty (that is, ""). The KeyEvent representing pressing the space bar is " ".

Try out lengthen-with-reset by creating a big-bang animation with lengthen-with-reset as the key handler and with draw. Run the animation, play with it, and comment it out when you are done.

3 Book exercises

Complete Exercises 83, 84, and 85 from Chapter 5 of the book. In order to receive full credit, you must design and use the helper functions mentioned in Exercise 84: string-first, string-rest, string-last, and string-remove-last.