Probably a crab would be filled with a sense of personal outrage
if it could hear us class it without ado or apology as a crustacean,
and thus dispose of it. "I am no such thing, it would say: I am
MYSELF, MYSELF alone."
- William James, The Varieties of Religious Experience
eq? is a function for letting us distinguish different crabs that would
otherwise look the same to us.
Let's say that we have two crabs c1 and c2.
;;;;;;;
;; In BSL:
;;;;;;;
(define-struct crab (name))
(define c1 (make-crab "joe"))
(define c2 (make-crab "joe"))
;;;;;;;
As it stands, we may want to say they are the same because they "look" the
same --- they have the same structural shape. equal? tells us that they
look the same.
;;;;;;
> (equal? c1 c2)
true
;;;;;;
But as William James notes, these crabs might be outraged at our lack of
crustacean discrimination. They may argue: we may look alike, but we are
different crabs. How shall we judge?
;;;;;;
> (eq? c1 c2)
false
;;;;;;
A crab is itself, itself alone:
;;;;;;
> (eq? c1 c1)
true
;;;;;;
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