delq string element in ido

delq string element in ido

[Leo]

In function `ido-kill-buffer-at-head', there's this form

    (delq buf ido-cur-list)

where buf is a string and ido-cur-list is a list of strings. I get this
by stepping through this function and checking the values of buf and
ido-cur-list. But delq uses `eq' to compare. Any idea why this function
still succeeds?

Leo

Re: delq string element in ido

[Andreas Schwab]

Leo <sdl.web@gmail.com> writes:

> In function `ido-kill-buffer-at-head', there's this form
>
>     (delq buf ido-cur-list)
>
> where buf is a string and ido-cur-list is a list of strings. I get this
> by stepping through this function and checking the values of buf and
> ido-cur-list. But delq uses `eq' to compare. Any idea why this function
> still succeeds?

Because `eq' returns t for identical Lisp objects.

Andreas.

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."

Re: delq string element in ido

[Leo]

2009/12/26 Andreas Schwab <schwab@linux-m68k.org>:
> Leo <sdl.web@gmail.com> writes:
>
>> In function `ido-kill-buffer-at-head', there's this form
>>
>>     (delq buf ido-cur-list)
>>
>> where buf is a string and ido-cur-list is a list of strings. I get this
>> by stepping through this function and checking the values of buf and
>> ido-cur-list. But delq uses `eq' to compare. Any idea why this function
>> still succeeds?
>
> Because `eq' returns t for identical Lisp objects.
>
> Andreas.

I don't quite get it.

If buf holds "str1" and ido-cur-list '("str1" "str2" "str3"), (delq
buf ido-cur-list) does not return '("str2" "str3"). But it does inside
ido-kill-buffer-at-head. That's where I am confused.

Could you explain a bit more? Thanks.

Leo

Re: delq string element in ido

[Teemu Likonen]

On 2009-12-26 12:13 (UTC), Leo wrote:

> 2009/12/26 Andreas Schwab <schwab@linux-m68k.org>:
>> Because `eq' returns t for identical Lisp objects.

> I don't quite get it.
>
> If buf holds "str1" and ido-cur-list '("str1" "str2" "str3"), (delq
> buf ido-cur-list) does not return '("str2" "str3"). But it does inside
> ido-kill-buffer-at-head. That's where I am confused.

It's not actually "identical Lisp objects"; eq is about the _same_ Lisp
object. Let me demonstrate:

    (setq my-list (list "one" "two")
          my-one (car my-list))

Internally my-one and (car my-list) refer to the same Lisp object:

    (eq my-one (car my-list))
    => t

But in the following examples the string "one" creates new Lisp object
which is different from the one referenced by my-one or (car my-list).

    (eq "one" (car my-list))
    => nil

    (eq "one" my-one)
    => nil

Re: delq string element in ido

[Eli Zaretskii]

> Date: Sat, 26 Dec 2009 12:13:22 +0000
> From: Leo <sdl.web@googlemail.com>
> Cc: Leo <sdl.web@gmail.com>, emacs-devel@gnu.org
> 
> If buf holds "str1" and ido-cur-list '("str1" "str2" "str3"), (delq
> buf ido-cur-list) does not return '("str2" "str3"). But it does inside
> ido-kill-buffer-at-head. That's where I am confused.

Probably because the value of buf comes from ido-cur-list, so it's the
same Lisp object as one of the strings in ido-cur-list.

Re: delq string element in ido

[Andreas Schwab]

Leo <sdl.web@googlemail.com> writes:

> If buf holds "str1" and ido-cur-list '("str1" "str2" "str3"), (delq
> buf ido-cur-list) does not return '("str2" "str3"). But it does inside
> ido-kill-buffer-at-head. That's where I am confused.

(setq buf (car ido-cur-list))
(eq (delq buf ido-cur-list) (cdr ido-cur-list))

Andreas.

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."

Re: delq string element in ido

[Leo]

On 2009-12-26 13:05 +0000, Andreas Schwab wrote:
> Leo <sdl.web@googlemail.com> writes:
>
>> If buf holds "str1" and ido-cur-list '("str1" "str2" "str3"), (delq
>> buf ido-cur-list) does not return '("str2" "str3"). But it does inside
>> ido-kill-buffer-at-head. That's where I am confused.
>
> (setq buf (car ido-cur-list))
> (eq (delq buf ido-cur-list) (cdr ido-cur-list))
>
> Andreas.

Thank you. Now I get it.

On 2009-12-26 12:37 +0000, Eli Zaretskii wrote:
>> Date: Sat, 26 Dec 2009 12:13:22 +0000
>> From: Leo <sdl.web@googlemail.com>
>> Cc: Leo <sdl.web@gmail.com>, emacs-devel@gnu.org
>> 
>> If buf holds "str1" and ido-cur-list '("str1" "str2" "str3"), (delq
>> buf ido-cur-list) does not return '("str2" "str3"). But it does inside
>> ido-kill-buffer-at-head. That's where I am confused.
>
> Probably because the value of buf comes from ido-cur-list, so it's the
> same Lisp object as one of the strings in ido-cur-list.

Indeed, it is due to ido-name.

On 2009-12-26 12:34 +0000, Teemu Likonen wrote:
[...]
>
> It's not actually "identical Lisp objects"; eq is about the _same_ Lisp
> object. Let me demonstrate:
>
>     (setq my-list (list "one" "two")
>           my-one (car my-list))
>
> Internally my-one and (car my-list) refer to the same Lisp object:
>
>     (eq my-one (car my-list))
>     => t
>
> But in the following examples the string "one" creates new Lisp object
> which is different from the one referenced by my-one or (car my-list).
>
>     (eq "one" (car my-list))
>     => nil
>
>     (eq "one" my-one)
>     => nil

Many thanks for the detailed explanation.

Leo