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Re: Surprising behavior of eq?
From: |
Zelphir Kaltstahl |
Subject: |
Re: Surprising behavior of eq? |
Date: |
Sun, 20 Sep 2020 14:19:46 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Icedove/68.10.0 |
Sorry, I misclicked "send" when I wanted to further edit my e-mail ...
My Guile version is:
~~~~
(version)
$6 = "3.0.4"
~~~~
On 20.09.20 14:16, Zelphir Kaltstahl wrote:
>
> Hello Guile users,
>
> I just noticed something weird about eq?.
>
> My Guile version is:
>
>
> I get the different results, depending on whether I define some
> bindings in a let or using define:
>
> (In Emacs Geiser:)
>
> ~~~~
> (define x '(10 9))
> (define y '(10 9))
> (eq? x y)
> $2 = #f
>
> (let ([x '(10 9)]
> [y '(10 9)])
> (eq? x y))
> $3 = #t
> ~~~~
>
> Is this intentional or a bug?
>
> I first noticed something strange when writing the following code:
>
> ~~~~DEFINITION~~~~
> (define make-multiple-list-remover
> (λ (equal-proc)
> (λ (lst unwanted)
> (let loop ([remaining-list lst])
> (cond
> [(null? remaining-list)
> '()]
> [(equal-proc (car remaining-list) unwanted)
> (loop (cdr remaining-list))]
> [else
> (cons (car remaining-list)
> (loop (cdr remaining-list)))])))))
> ~~~~
>
> ~~~~TEST~~~~
> (let ([a '(9 10)]
> [b '(9 10)])
> (test-equal "make-multiple-list-remover-03"
> `(1 2 (3) (4) ,a)
> ((make-multiple-list-remover eq?)
> `(a b (c) (d) ,a) b)))
> ~~~~
>
> I was wondering, why the test fails. I think (eq? ...) should not be
> able to see the equivalence of both lists a and b, just like when
> defined using (define ...).
>
> I can also run it in the REPL and see the difference:
>
> ~~~~
> (define a '(9 10))
> (define b '(9 10))
> ((make-multiple-list-remover eq?)
> `(a b (c) (d) ,a) b)
> $4 = (a b (c) (d) (9 10))
>
> (let ([a '(9 10)]
> [b '(9 10)])
> ((make-multiple-list-remover eq?)
> `(a b (c) (d) ,a) b))
> $5 = (a b (c) (d))
> ~~~~
>
> Somehow the bindings of let seem to be different from the bindings
> created using define. What about using define inside let?
>
> ~~~~
>
> ~~~~
> --
> repositories: https://notabug.org/ZelphirKaltstahl
Somehow the bindings of let seem to be different from the bindings
created using define. What about using define inside let?
~~~~
(let ([unrelated 'bla])
(define a '(9 10))
(define b '(9 10))
((make-multiple-list-remover eq?)
`(a b (c) (d) ,a) b))
$7 = (a b (c) (d))
~~~~
So there the define usage also differs from when I use define on the top
level. Perhaps that is the difference? On which level the bindings are
defined?
Regards,
Zelphir
--
repositories: https://notabug.org/ZelphirKaltstahl
- Surprising behavior of eq?, Zelphir Kaltstahl, 2020/09/20
- Re: Surprising behavior of eq?,
Zelphir Kaltstahl <=
- Re: Surprising behavior of eq?, Christopher Lemmer Webber, 2020/09/20
- Re: Surprising behavior of eq?, Zelphir Kaltstahl, 2020/09/20
- Re: Surprising behavior of eq?, John Cowan, 2020/09/20
- Re: Surprising behavior of eq?, Zelphir Kaltstahl, 2020/09/20
- Re: Surprising behavior of eq?, tomas, 2020/09/20
- Re: Surprising behavior of eq?, John Cowan, 2020/09/20
- Re: Surprising behavior of eq?, Linus Björnstam, 2020/09/20
- Re: Surprising behavior of eq?, John Cowan, 2020/09/20
- Re: Surprising behavior of eq?, Stefan Schmiedl, 2020/09/20
- Re: Surprising behavior of eq?, Zelphir Kaltstahl, 2020/09/20