Structures

This is Chapter 20 in the text. Since this is the pro section, I include details you would not usually see.

1. Using #lang racket allows some advanced features at a cost of some complexity.
2. Every struct needs #:transparent. This is best explained as a design mistake in the Racket language.
3. Read about struct-copy or follow the examples below.

#lang racket
(require lang/posn)
(define-struct m (pos vel color) #:transparent)
(define example-1
    (make-m (make-posn 5 12) 
	        (make-posn 2 -1) 
			(make-color 255 100 0)))

(define example-2
    (struct-copy m example-1 [vel (make-posn -3 4)]))

Check-expects

In #lang racket you need to do checks using the rackunit module.

You need to use check-equal? or do what I do and create an alias for check-expect.

(require rackunit)
(define check-expect check-equal?)