[racket] clarification for beginners please
I have a group of high school students with a question... can someone
please explain to beginner Racket users the differences between these three
boolean functions: eq? equal? eqv?
We have read the help menu verbage visible from DrRacket, but simply don't
understand what it is saying. Maybe that's lack of context or
vocabulary... but we're struggling a bit. To test simple variations of
application, we wrote some simple code (shown below) but don't understand
why the results are what they are:
(define FOUR "four")
(define A (make-posn 4 5))
(define B (make-posn (+ 3 1) (- 6 1)))
"-------------"
(equal? FOUR "four")
(equal? 4 (+ 1 3))
(equal? 4 (posn-x (make-posn 4 3)))
(equal? A B)
"-------------"
(eq? FOUR "four")
(eq? 4 (+ 1 3))
(eq? 4 (posn-x (make-posn 4 3)))
(eq? A B)
"---------------"
(eqv? FOUR "four")
(eqv? 4 (+ 1 3))
(eqv? 4 (posn-x (make-posn 4 3)))
(eqv? A B)
Why in the world would the above-defined A and B be considered "equal?" but
not "eq?" or "eqv?"?
--
*Joe Ford
Technology Resources, Scheduling & Yearbook
Holland Hall
jford at hollandhall.org
*
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