Generating an unique symbol in elisp

Generating an unique symbol in elisp

[Alin Soare]

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A very useful function for generating private environments is the
(gensym&optional x) in common lisp. It can replace in some places the
closures.


In Clisp it is defined in C something like this:

char*
gensym (char *x)
{
 static int x;
 char a[100];
 snprintf(a, 100, "%s%d", x? x:"G",  x++);
 return strdup (a);
}

Does this function already exist in elisp ? I looked in the manual and did
not find it...


Alin
*

---
*
Wenn ich 'Kultur' höre, nehme ich meine Pistole
Hermann Göring
*
*

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Re: Generating an unique symbol in elisp

[Edward O'Connor]

> Does this function already exist in elisp ? I looked in the manual and did
> not find it...

`make-symbol' creates uninterned symbols.


Ted

Re: Generating an unique symbol in elisp

[Alin Soare]

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> Does this function already exist in elisp ? I looked in the manual and did
> > not find it...
>
> `make-symbol' creates uninterned symbols.
>


The name is the problem. Does it generate an uninexistent name, or have I
write a function to generate the uninexistent name ?

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Re: Generating an unique symbol in elisp

[Andreas Schwab]

Alin Soare <as1789@gmail.com> writes:

> Does this function already exist in elisp ? I looked in the manual and did
> not find it...

gensym is a compiled Lisp function in `cl-macs.el'.

(gensym &optional PREFIX)

Generate a new uninterned symbol.
The name is made by appending a number to PREFIX, default "G".

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: Generating an unique symbol in elisp

[Alin Soare]

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> > Does this function already exist in elisp ? I looked in the manual and
> did
> > not find it...
>
> gensym is a compiled Lisp function in `cl-macs.el'.
>
> (gensym &optional PREFIX)
>
> Generate a new uninterned symbol.
> The name is made by appending a number to PREFIX, default "G".
>
>
LOL. Tabs defined as windows configurations must work without (require 'cl)
.



Alin.

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Re: Generating an unique symbol in elisp

[Edward O'Connor]

> The name is the problem. Does it generate an uninexistent name, or have I
> write a function to generate the uninexistent name ?

The name isn't the problem. You can (make-symbol "foo") a bunch of
times, and you'll have a bunch of different symbols. That's what it
means for them to be uninterned.


Ted

Re: Generating an unique symbol in elisp

[Alin Soare]

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2010/12/4 Edward O'Connor <hober0@gmail.com>

> > The name is the problem. Does it generate an uninexistent name, or have I
> > write a function to generate the uninexistent name ?
>
> The name isn't the problem. You can (make-symbol "foo") a bunch of
> times, and you'll have a bunch of different symbols. That's what it
> means for them to be uninterned.
>

Good.

Can you bind a value in variable field/ evaluate a symbol as a variable if
it is not interned ?

Otherwise, can you create an obarray (different of main obarr) and intern
within it only a few symbols (in this case the matter ), and evaluate within
that environment ?

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RE: Generating an unique symbol in elisp

[Drew Adams]

> can you create an obarray (different of main obarr) and intern
> within it only a few symbols (in this case the matter ), and
> evaluate within that environment ?

Yes.  That's the idea behind having separate obarrays.

There are no doubt examples of this in the Lisp sources.
If not, here is one: http://www.emacswiki.org/emacs/synonyms.el.
	
	

Re: Generating an unique symbol in elisp

[Stefan Monnier]

> A very useful function for generating private environments is the
> (gensym&optional x) in common lisp. It can replace in some places the
> closures.
> Does this function already exist in elisp ? I looked in the manual and did
> not find it...

It's called make-symbol.


        Stefan

Re: Generating an unique symbol in elisp

[Alin Soare]

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2010/12/4 Drew Adams <drew.adams@oracle.com>

> > can you create an obarray (different of main obarr) and intern
> > within it only a few symbols (in this case the matter ), and
> > evaluate within that environment ?
>
> Yes.  That's the idea behind having separate obarrays.
>
> There are no doubt examples of this in the Lisp sources.
> If not, here is one: http://www.emacswiki.org/emacs/synonyms.el.
>
>
>
>
Thanks.

Tomorrow I send the minimal completions I need for tabs within C code, and
the lisp scripts that define tabs as window-configuration.

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Re: Generating an unique symbol in elisp

[Stefan Monnier]

> Can you bind a value in variable field/ evaluate a symbol as a variable if
> it is not interned ?

Yes.  The fact that it's interned or not only affects the Lisp reader,
not the interpreter.

> Otherwise, can you create an obarray (different of main obarr) and intern
> within it only a few symbols (in this case the matter ),

Yes.

> and evaluate within that environment ?

Elisp does not have such a notion, no.


        Stefan