Week 9 Set b

Due Date Wed at 9pm (Week 9)

Purpose To practice the design of functions on multi-recursive data definitions

Finger Exercises

Exercise 1 From HtDP, 324 and 325.

Graded Exercises

Exercise 2 Your friends and you decided to create a maze exploration software. In the spirit of iterative refinement, you have decided to start with a simple model of mazes. In this simplest form, rooms in the maze always contain a single object and have always four exits, though some of them might be blocked. Here is one way to represent this choice as data:

(define-struct room (object north east south west))

; A Room is a structure:

;    (make-room Symbol Exit Exit Exit Exit)

; An Exit is [Maybe Room], meaning it is one of:

; – #false

; – Room

; interpretation (make-room 'ax r1 r2 r3 r4) describes a room

; in a maze. The room contains an 'ax. Its Exits lead to four other

; rooms: r1, ..., r4, through the door to the north, east, south,

; west, respectively. If an Exit is #false, the door is locked.

To find out whether this representation can be easily processed, you have decided to design the function all-objects, which consumes a Room and produces the list of all objects it can find by traversing the entire maze.

Suggestion You may wish to use check-satisfied to formulate tests. See HtDP/2e for examples or consider this one:

; Number -> [Number -> Boolean]

; produce a function that checks whether some number is

; between 0 (inclusive) and n (exclusive)

(define (between-0-and n)

(local (; Number -> Boolean

; is x between 0 (inclusive) and n (exclusive)

(define (between x) (and (<= 0 x) (< x n))))

between))

(check-satisfied (random 10) (between-0-and 10))