On Fri, Apr 26, 2013 at 4:19 AM, Robby Findler
wrote:
> You wouldn't happen to have a citation for this traditional way, would you?
>
No. But I'll take note if I happen to remember some place where it is
explained in this way.
Racket Users list:
http://lists.racket-lang.
Opaque structures are inaccessible to all operations, including equality.
That's why only (eq? z y) can succeed because z and y point to the same object
and eq? compares the pointers not the objects.
This opacity is needed to ensure the integrity of values created by the core
(lambdas) and by
You wouldn't happen to have a citation for this traditional way, would you?
tia,
Robby
On Thu, Apr 25, 2013 at 9:11 PM, Pierpaolo Bernardi wrote:
> Ah, yes, right.
>
>
>
> On Fri, Apr 26, 2013 at 4:09 AM, Robby Findler <
> ro...@eecs.northwestern.edu> wrote:
>
>> Yes, except that we do know som
Alan Johnsey wrote at 04/25/2013 10:04 PM:
(define x (make-posn 4 5))
(define y (make-posn 4 5))
[...]
> (equal? x y)
#f
[...]
Adding #:transparent to the posn struct definition makes x equal? to
both y and z as it should, and eq? gives #f when comparing x and y as
it should.
Seem
Ah, yes, right.
On Fri, Apr 26, 2013 at 4:09 AM, Robby Findler
wrote:
> Yes, except that we do know something about what happens when it returns
> #t in the "in all other cases" case.
>
> Robby
>
>
> On Thu, Apr 25, 2013 at 9:03 PM, Pierpaolo Bernardi
> wrote:
>
>> The traditional way of expla
Yes, except that we do know something about what happens when it returns #t
in the "in all other cases" case.
Robby
On Thu, Apr 25, 2013 at 9:03 PM, Pierpaolo Bernardi wrote:
> The traditional way of explaining eq? is that it works when one of the
> arguments is a symbol or a mutable data struc
I've followed this discussion and thought I understood it quite well until I
tried it. Following are my results, using Racket 3.3 on Windows XP:
Test 1:
#lang racket
(define-struct posn (x y))
(define x (make-posn 4 5))
(define y (make-posn 4 5))
(define z y)
> (equal? x y)
#f
> (
The traditional way of explaining eq? is that it works when one of the
arguments is a symbol or a mutable data structure. In all other cases the
result is implementation dependent. Is this explanation still valid for
racket?
On Fri, Apr 26, 2013 at 1:37 AM, Robby Findler
wrote:
> I don't thin
I don't think that either of these explanations are really the right way to
think about eq?. The only way to really understand eq? on immutable values
is to understand that it is exposing low-level details of the
implementation to you (ostensibly for performance reasons). That is, if
(eq? a b) retu
On Thu, Apr 25, 2013 at 5:35 PM, Matthias Felleisen
wrote:
> eqv? is Scheme's attempt at incorporating an approximation to the so-called
> notion of observational equivalence. Two values are observationally
> equivalent if they are interchangeable in all contexts -- wherever you see
> one value
On Apr 25, 2013, at 4:57 PM, David Vanderson wrote:
>
> On 04/25/2013 02:57 PM, Matthias Felleisen wrote:
>>> (eqv? (factorial 1000) (factorial 1000)) ;; ... but they point to
>>> observably equal numbers, so eqv? uses = to compare them
>> #t
>>> (eqv? (cons 1 2) (cons 1 2)) ;; distinct pointe
On 04/25/2013 02:57 PM, Matthias Felleisen wrote:
(eqv? (factorial 1000) (factorial 1000)) ;; ... but they point to observably
equal numbers, so eqv? uses = to compare them
#t
(eqv? (cons 1 2) (cons 1 2)) ;; distinct pointers point to allocated
structures, on the other hand, and eqv? compare
Joe,
Perhaps a more pedestrian explanation might help. There is a difference
between two items having the same value and two items being the same item.
equal? tests if its two items have the same value.
eq? tests if two items are the same item.
Using your example:
(define A (make-posn 4 5))
(d
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 Religiou
On Apr 25, 2013, at 2:31 PM, "Ford, Joe" wrote:
> 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?
Welcome to Racket v5.3.4.5.
> (require math)
> (eq?
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