* Problem understanding set-register syntax
@ 2010-12-05 9:51 Aurélien Bottazzini
2010-12-06 22:23 ` Drew Adams
0 siblings, 1 reply; 5+ messages in thread
From: Aurélien Bottazzini @ 2010-12-05 9:51 UTC (permalink / raw)
To: help-gnu-emacs
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Hello everyone,
in my init.el I have
(set-register ?i '(file . "~/.emacs.d/init.el"))
which allows me to quickly jump to my init file using C-x r j i
But I don't really understand the syntax.
Why do I have to use the exclamation mark when I set the register?
Why can't I just use:
(set-register i '(file . "~/.emacs.d/init.el")) ; will say Symbol's value as
variable is void:i
I tried to search in the documentation for set-register and variable
definition but I did not find
anything to really explain it.
Thanks for any help.
Aurélien
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^ permalink raw reply [flat|nested] 5+ messages in thread
* RE: Problem understanding set-register syntax
2010-12-05 9:51 Problem understanding set-register syntax Aurélien Bottazzini
@ 2010-12-06 22:23 ` Drew Adams
2010-12-06 22:54 ` Drew Adams
0 siblings, 1 reply; 5+ messages in thread
From: Drew Adams @ 2010-12-06 22:23 UTC (permalink / raw)
To: 'Aurélien Bottazzini', help-gnu-emacs
> in my init.el I have
> (set-register ?i '(file . "~/.emacs.d/init.el"))
> which allows me to quickly jump to my init file using C-x r j i
> But I don't really understand the syntax.
> Why do I have to use the exclamation mark when I set the register?
You mean question mark, I think.
> Why can't I just use:
> (set-register i '(file . "~/.emacs.d/init.el"))
> ; will say Symbol's value as variable is void:i
Because the first argument to `set-register' is a register name, which is a
character, and `?i' is the Lisp syntax for the character `i'.
> I tried to search in the documentation for set-register and
> variable definition but I did not find anything to really explain it.
Please file a doc bug for `C-h f set-register'. The doc should say clearly what
each parameter is. In this case it says nothing about the first parameter
except that it is a register. It expects readers to somehow know that a
register (its name, that is) is of type character.
Relevant doc that will help you:
1. Elisp manual, node `Registers':
"A register is a sort of variable used in Emacs editing that
can hold a variety of different kinds of values. Each
register is named by a single character."
IOW, a register is like a variable in that it has a name and a value. The name
is a character, however, not a symbol.
2. Emacs manual, node `Registers':
"Emacs "registers" are compartments where you can save text, rectangles,
positions, and other things for later use....
Each register has a name that consists of a single character, which
we will denote by R; R can be a letter (such as `a') or a number (such
as `1'); case matters, so register `a' is not the same as register `A'."
^ permalink raw reply [flat|nested] 5+ messages in thread
* RE: Problem understanding set-register syntax
2010-12-06 22:23 ` Drew Adams
@ 2010-12-06 22:54 ` Drew Adams
0 siblings, 0 replies; 5+ messages in thread
From: Drew Adams @ 2010-12-06 22:54 UTC (permalink / raw)
To: 'Aurélien Bottazzini', help-gnu-emacs
> > Why can't I just use:
> > (set-register i '(file . "~/.emacs.d/init.el"))
> > ; will say Symbol's value as variable is void:i
>
> Because the first argument to `set-register' is a register
> name, which is a character, and `?i' is the Lisp syntax for
> the character `i'.
I should also have mentioned that using just i, without quoting it (i.e., 'i)
causes the symbol i to be evaluated. And since the symbol i has no value here
(no global value) you get the error message saying that its value is void.
Some symbols, such as t and nil (and all keywords, such as :foobar) are
self-evaluating, meaning that they act just like variables whose values are the
symbols themselves. You do not need to quote self-evaluating symbols in an
evaluation context. Other symbols (e.g. i, foobar) you do need to quote, if you
want not the value of the symbol (e.g. it might not have a value) but the symbol
itself.
But all characters are self-evaluating, so ?i evaluates to ?i.
See the Emacs manual, node `Init Syntax'.
See the Elisp manual, node `Basic Char Syntax'.
(Use `g' in Info to go to a particular node.)
^ permalink raw reply [flat|nested] 5+ messages in thread
* Problem understanding set-register syntax
@ 2010-12-06 13:47 Aurélien Bottazzini
2010-12-06 22:46 ` PJ Weisberg
0 siblings, 1 reply; 5+ messages in thread
From: Aurélien Bottazzini @ 2010-12-06 13:47 UTC (permalink / raw)
To: help-gnu-emacs
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(sorry if this email is a duplicate, but the first one was lost apparently)
Hello everyone,
in my init.el I have
(set-register ?i '(file . "~/.emacs.d/init.el"))
which allows me to quickly jump to my init file using C-x r j i
But I don't really understand the syntax.
Why do I have to use the exclamation mark when I set the register?
Why can't I just use:
(set-register i '(file . "~/.emacs.d/init.el")) ; will say Symbol's value as
variable is void:i
I tried to search in the documentation for set-register and variable
definition but I did not find
anything to really explain it.
Thanks for any help.
Aurélien
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^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: Problem understanding set-register syntax
2010-12-06 13:47 Aurélien Bottazzini
@ 2010-12-06 22:46 ` PJ Weisberg
0 siblings, 0 replies; 5+ messages in thread
From: PJ Weisberg @ 2010-12-06 22:46 UTC (permalink / raw)
To: help-gnu-emacs
On Mon, Dec 6, 2010 at 5:47 AM, Aurélien Bottazzini
<aurelien.bottazzini@gmail.com> wrote:
> (sorry if this email is a duplicate, but the first one was lost apparently)
> Hello everyone,
> in my init.el I have
> (set-register ?i '(file . "~/.emacs.d/init.el"))
> which allows me to quickly jump to my init file using C-x r j i
> But I don't really understand the syntax.
> Why do I have to use the exclamation mark when I set the register?
> Why can't I just use:
> (set-register i '(file . "~/.emacs.d/init.el")) ; will say Symbol's value as
> variable is void:i
> I tried to search in the documentation for set-register and variable
> definition but I did not find
> anything to really explain it.
> Thanks for any help.
> Aurélien
English:
!: exclamation mark (more commonly "exclamation point")
?: question mark
Emacs:
?i: The character 'i' (which, technically, is equal to the number 105).
i: A variable represented by the symbol i.
Consider the difference between:
int i = 0;
and
int 'i' = 0;
-PJ
^ permalink raw reply [flat|nested] 5+ messages in thread
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2010-12-05 9:51 Problem understanding set-register syntax Aurélien Bottazzini
2010-12-06 22:23 ` Drew Adams
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2010-12-06 13:47 Aurélien Bottazzini
2010-12-06 22:46 ` PJ Weisberg
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