From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Tom Breton (Tehom)" Subject: Re: Docs submitted (Was Re: Advice sought on managing decision alternatives.) Date: Wed, 11 Feb 2009 23:17:52 -0500 (EST) Message-ID: <1555.65.96.63.84.1234412272.squirrel@mail.panix.com> References: <20090101170227.C707734803@mail2.panix.com> <1036.24.63.0.170.1233950825.squirrel@mail.panix.com> <60BDFE6D-6B8C-4A23-A737-67DC1F523C79@uva.nl> <1044.66.30.185.29.1234039592.squirrel@mail.panix.com> <6444D654-9B7B-415D-A6DB-F3BADCB1EE2A@uva.nl> <1451.24.63.21.131.1234124707.squirrel@mail.panix.com> <8BD25355-1218-4DB5-9C85-77EA011540D0@uva.nl> <1555.24.62.30.15.1234235653.squirrel@mail.panix.com> <1062.24.62.30.15.1234314505.squirrel@mail.panix.com> <1330.65.96.63.84.1234388462.squirrel@mail.panix.com> <19798.1234395529@alphaville.usa.hp.com> Mime-Version: 1.0 Content-Type: text/plain;charset=iso-8859-1 Content-Transfer-Encoding: quoted-printable Return-path: Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1LXT1O-0005QJ-Vy for emacs-orgmode@gnu.org; Wed, 11 Feb 2009 23:17:55 -0500 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1LXT1N-0005Q7-Bl for emacs-orgmode@gnu.org; Wed, 11 Feb 2009 23:17:54 -0500 Received: from [199.232.76.173] (port=49569 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1LXT1N-0005Q4-6B for emacs-orgmode@gnu.org; Wed, 11 Feb 2009 23:17:53 -0500 Received: from mail2.panix.com ([166.84.1.73]:57178) by monty-python.gnu.org with esmtp (Exim 4.60) (envelope-from ) id 1LXT1M-0005kU-T1 for emacs-orgmode@gnu.org; Wed, 11 Feb 2009 23:17:53 -0500 In-Reply-To: <19798.1234395529@alphaville.usa.hp.com> List-Id: "General discussions about Org-mode." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: emacs-orgmode-bounces+geo-emacs-orgmode=m.gmane.org@gnu.org Errors-To: emacs-orgmode-bounces+geo-emacs-orgmode=m.gmane.org@gnu.org To: nicholas.dokos@hp.com Cc: emacs-orgmode@gnu.org nicholas.dokos@hp.com wrote: > Tom Breton (Tehom) wrote: >> (let* >> ((x 1)) >> (eval-after-load 'simple (setq x 2)) >> x) >> >> =3D3D> 2 >> >> >> >> (let* >> ((x 1)) >> (eval-after-load 'simple '(setq x 2)) >> x) >> >> =3D3D> 1 > > > Are you sure about this? My understanding of this differs from > yours: This is definitely a "Boy is my face red" moment. You are completely correct. I had misunderstood `eval-after-load' as a macro. Upon looking at subr.el, it is obvious that you are right and I am wrong. Thank you for pointing all that out. > eval-after-load is an ordinary function (not a special form), and > function evaluation in most LISPs (elisp in particular) evaluates > arguments before the function is called on them. So if you give it an > unquoted form, the form will be evaluated *before* eval-after-load gets > its hands on it. That seems to me to defeat the purpose. I'd think that > the thing to do is to give the quoted form as argument, then function > evaluation evaluates the argument (i.e. unquotes the quoted form, > giving back the form) which is then passed to eval-after-load for > action. The semantics of eval-after-load imply that (depending on > whether the library is already loaded or not) the form may be evaluated > once. It is then squirrelled away and if the library is ever loaded > again, it is evaluated (perhaps for the first time, perhaps for the > nth), *after* the library is loaded. > > And I think your demonstration is misleading: after doing the > eval-after-load, you need to reload "simple" to trigger the "after-load= " > evaluation, otherwise eval-after-load reduces to just plain eval (in > this particular case, since simple is, as you point out, already loade= d - > things would be different if you had chosen some obscure library that > is not already loaded): > > (let* > ((x 1)) > (eval-after-load 'simple (setq x 2)) > (load-library "simple") > x) > 2 > > (let* > ((x 1)) > (eval-after-load 'simple '(setq x 2)) > (load-library "simple") > x) > 2 > > In the first case, (setq x 2) was evaluated, x was set to 2 and 2 was > passed into eval-after-load. Assuming that simple is already loaded, th= e > 2 is evaluated: the result is 2 and it is just thrown away. After the > library is loaded again, 2 is evaluated again and the result is 2 and i= t > just thrown away. Since x was set to 2 before, the value of x is 2. > > In the second case, (quote (setq x 2)) is evaluated, so the form (setq = x > 2) is passed to eval-after-load. Assuming that simple is already loaded= , > the form is evaluated, setting x to 2 and giving a result of 2 (which i= s > thrown away). After the library is loaded, (setq x 2) is eval'led again= , > setting x to 2 again, and giving a result of 2 (which is thrown away). > > In both cases, the value of x (and therefore the value the let* form > returns) is 2. But it seems to me that the second case is the useful > one. > > Perhaps the most telling evidence that the quote should be there howeve= r > is the following: if you look at eval-after-load instances in the emacs > lisp directory, you'll see that the second argument in all of them is > quoted or at least (when partial evaluation is required) backquoted -- > although I guess one could argue that they all originated by copying a > badly constructed precursor - the programming version of original sin!-= ) > > Regards, > Nick > >