Prev: cosx - sinx + 3x2
Next: Yet another 'when to use macros' question....
From: Mike on 28 Jan 2006 11:11
What's the difference? My first exposure to lisp
many years ago I did everything with setq.

Mike
From: Ulrich Hobelmann on 28 Jan 2006 11:23
Mike wrote:
> What's the difference? My first exposure to lisp
> many years ago I did everything with setq.

SETQ works for normal variables. With SETF you can set whole fields (in
fact that's how I memorize the name), like (setf (cdr *foo*) 5), but for
all kinds of things...

I guess most people don't even bother to use SETQ, because SETF
auto-expands to SETQ if appropriate, i.e. for variables.

--
Suffering from Gates-induced brain leakage...
From: Barry Margolin on 28 Jan 2006 11:24
In article <QIMCf.2185$r74.1865(a)fe06.lga>, Mike <mikee(a)mikee.ath.cx>
wrote:

> What's the difference? My first exposure to lisp
> many years ago I did everything with setq.

SETQ can only assign to variables, SETF can assign to many different
types of containers. For instance, you can do:

(setf (car some-cons-cell) 3)

--
Barry Margolin, barmar(a)alum.mit.edu
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***
*** PLEASE don't copy me on replies, I'll read them in the group ***
From: Jeff M. on 28 Jan 2006 11:39
This is something that actually took me quite a long time to learn, and
most of the explanations I got were both correct, and either mysterious
or didn't really hit home. Here's my attempt to help you with it. :-)

SETQ is the simple method of binding a symbol to a value. Keep in mind,
that's all it does. It binds a symbol to a value:

(setq x 10)
(setq list '(a b c))

SETF is an extendable macro. It is a macro that expands to the proper
form required to bind "something" to a value. That "something" is the
key. For example, when setting the value in a hash table or place in an
array, you use SETF:

(setf (gethash :my-key table) 10)
(setf (aref array 2 4) '(a b c))

You can extend the definition of SETF using DEFSETF
(http://www.lispworks.com/documentation/HyperSpec/Body/m_defset.htm#defsetf).
99% of the time, you should just use SETF. If you SETF a symbol, it
will expand to a SETQ.

Hope this helps,

Jeff M.

From: Mike on 28 Jan 2006 12:02
On 2006-01-28, Jeff M. <massung(a)gmail.com> wrote:
> This is something that actually took me quite a long time to learn, and
> most of the explanations I got were both correct, and either mysterious
> or didn't really hit home. Here's my attempt to help you with it. :-)
>
> SETQ is the simple method of binding a symbol to a value. Keep in mind,
> that's all it does. It binds a symbol to a value:
>
> (setq x 10)
> (setq list '(a b c))
>
> SETF is an extendable macro. It is a macro that expands to the proper
> form required to bind "something" to a value. That "something" is the
> key. For example, when setting the value in a hash table or place in an
> array, you use SETF:
>
> (setf (gethash :my-key table) 10)
> (setf (aref array 2 4) '(a b c))
>
> You can extend the definition of SETF using DEFSETF
> (http://www.lispworks.com/documentation/HyperSpec/Body/m_defset.htm#defsetf).
> 99% of the time, you should just use SETF. If you SETF a symbol, it
> will expand to a SETQ.
>
> Hope this helps,
>
> Jeff M.
>

Thank you all for the explanations.

Mike
 |  Next  |  Last
Pages: 1 2 3 4
Prev: cosx - sinx + 3x2
Next: Yet another 'when to use macros' question....