From: "Tom Breton (Tehom)" <email@example.com> To: firstname.lastname@example.org Cc: email@example.com Subject: Re: Docs submitted (Was Re: Advice sought on managing decision alternatives.) Date: Wed, 11 Feb 2009 23:17:52 -0500 (EST) [thread overview] Message-ID: <firstname.lastname@example.org> (raw) In-Reply-To: <email@example.com> firstname.lastname@example.org wrote: > Tom Breton (Tehom) <email@example.com> wrote: >> (let* >> ((x 1)) >> (eval-after-load 'simple (setq x 2)) >> x) >> >> =3D> 2 >> >> >> >> (let* >> ((x 1)) >> (eval-after-load 'simple '(setq x 2)) >> x) >> >> =3D> 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 loaded - > 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, the > 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 it > 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 is > 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 however > 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 > >
next prev parent reply other threads:[~2009-02-12 4:17 UTC|newest] Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top [not found] <20090101170227.C707734803@mail2.panix.com> 2009-01-01 22:53 ` Feature request and patch - blocked TODO to say BLOCKED Tom Breton (Tehom) 2009-01-09 8:16 ` Carsten Dominik 2009-01-15 2:34 ` Tom Breton (Tehom) 2009-01-17 8:01 ` Carsten Dominik 2009-01-19 3:33 ` Advice sought on managing decision alternatives Tom Breton (Tehom) 2009-01-22 11:15 ` Carsten Dominik 2009-01-31 4:21 ` Tom Breton (Tehom) 2009-01-31 5:41 ` Carsten Dominik 2009-01-31 18:36 ` Tom Breton (Tehom) 2009-02-01 15:54 ` James TD Smith 2009-02-06 13:08 ` Carsten Dominik 2009-02-06 16:16 ` William Henney 2009-02-06 20:07 ` Tom Breton (Tehom) 2009-02-07 0:18 ` Carsten Dominik 2009-02-07 20:46 ` Tom Breton (Tehom) 2009-02-08 13:06 ` Carsten Dominik 2009-02-08 20:25 ` Tom Breton (Tehom) 2009-02-09 6:42 ` Carsten Dominik 2009-02-10 3:14 ` Docs submitted (Was Re: Advice sought on managing decision alternatives.) Tom Breton (Tehom) 2009-02-10 7:55 ` Carsten Dominik 2009-02-24 0:51 ` org-choose bugfix Tom Breton (Tehom) 2009-02-24 3:05 ` Manish 2009-04-07 0:13 ` Tom Breton (Tehom) 2009-04-08 13:13 ` Carsten Dominik 2009-02-24 5:51 ` Carsten Dominik 2009-02-10 8:46 ` Docs submitted (Was Re: Advice sought on managing decision alternatives.) Manish 2009-02-10 9:12 ` Carsten Dominik 2009-02-10 10:26 ` Manish 2009-02-10 22:48 ` Tom Breton (Tehom) 2009-02-12 12:50 ` Manish 2009-02-12 20:13 ` Tom Breton (Tehom) 2009-02-13 4:23 ` Manish 2009-02-12 20:55 ` Patch " Tom Breton (Tehom) 2009-02-13 4:38 ` Manish 2009-02-11 1:08 ` Tom Breton (Tehom) 2009-02-11 10:34 ` Carsten Dominik 2009-02-11 21:41 ` Tom Breton (Tehom) 2009-02-11 23:38 ` Nick Dokos 2009-02-12 4:17 ` Tom Breton (Tehom) [this message] 2009-02-11 23:44 ` Carsten Dominik 2009-02-12 4:27 ` Tom Breton (Tehom) 2009-02-12 15:49 ` Nick Dokos 2009-02-12 20:32 ` Tom Breton (Tehom) 2009-02-12 21:25 ` Nick Dokos 2009-02-11 12:29 ` Carsten Dominik 2009-02-11 14:58 ` Docs submitted Bernt Hansen 2009-02-11 17:33 ` Samuel Wales 2009-02-11 15:38 ` Docs submitted (Was Re: Advice sought on managing decision alternatives.) Daniel Clemente 2009-02-11 15:41 ` Carsten Dominik 2009-02-11 20:02 ` Tom Breton (Tehom) 2009-02-11 23:45 ` Carsten Dominik 2009-02-11 1:45 ` Slight fix to update-org.sh Tom Breton (Tehom) 2009-02-10 23:19 ` Docs submitted (Was Re: Advice sought on managing decision alternatives.) Tom Breton (Tehom) 2009-02-11 10:34 ` Carsten Dominik 2009-02-10 22:45 ` Tom Breton (Tehom)
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