From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Philip Kaludercic Newsgroups: gmane.emacs.help Subject: Re: macros and macroexpand Date: Mon, 07 Aug 2023 14:22:58 +0000 Message-ID: <87wmy7rkxp.fsf@posteo.net> References: Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="15163"; mail-complaints-to="usenet@ciao.gmane.io" Cc: Yuri Khan , Heime via Users list for the GNU Emacs text editor To: Heime Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org Mon Aug 07 16:23:37 2023 Return-path: Envelope-to: geh-help-gnu-emacs@m.gmane-mx.org Original-Received: from lists.gnu.org ([209.51.188.17]) by ciao.gmane.io with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1qT18y-0003gj-RI for geh-help-gnu-emacs@m.gmane-mx.org; Mon, 07 Aug 2023 16:23:36 +0200 Original-Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1qT18W-0005OB-Vo; Mon, 07 Aug 2023 10:23:09 -0400 Original-Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qT18U-0005Nw-A0 for help-gnu-emacs@gnu.org; Mon, 07 Aug 2023 10:23:06 -0400 Original-Received: from mout02.posteo.de ([185.67.36.66]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qT18R-0007Iv-PD for help-gnu-emacs@gnu.org; Mon, 07 Aug 2023 10:23:06 -0400 Original-Received: from submission (posteo.de [185.67.36.169]) by mout02.posteo.de (Postfix) with ESMTPS id A6081240104 for ; Mon, 7 Aug 2023 16:22:59 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=posteo.net; s=2017; t=1691418179; bh=Mg68dYYL9bLUIh+2T6LfwDXvQ/lUh5ggCKPQ3h01Mmc=; h=From:To:Cc:Subject:Autocrypt:Date:Message-ID:MIME-Version: Content-Transfer-Encoding:From; b=l3L5lYwiz3CkKw6rb64H06t2byw7k6OvyVOqT8zuyUY7BgoviTKVQ7m7bG6Vr6QPP Pf78dV414D2wmctaVDzqY1OxNXYeWqVTYKlWbk2fdDgTAygO9oJJE0lpUE3HA3R/Pb De2Qvxdg8TCRaHK9TRHCVHmHzDSG08Zew19hVaAHZ8MyLmkwZNWgY0uNqkPtxDyBAd 6kk0h8Uxu63QRxgidv6zvZiJSMeY+BWY1wXXKVJeDNt/aEt9U2W6vcJQs1o3WvDA3/ xpGmyrWE9oTdkUQUJrZHeFo5OlUtjv+IylcPDnxHp2L4zikaaAaPJyCmmeahcOI0ay MUOwXRNdIXwFw== Original-Received: from customer (localhost [127.0.0.1]) by submission (posteo.de) with ESMTPSA id 4RKJSg0pT3z6twV; Mon, 7 Aug 2023 16:22:59 +0200 (CEST) In-Reply-To: (Heime's message of "Mon, 07 Aug 2023 12:43:13 +0000") Autocrypt: addr=philipk@posteo.net; keydata= mDMEZBBQQhYJKwYBBAHaRw8BAQdAHJuofBrfqFh12uQu0Yi7mrl525F28eTmwUDflFNmdui0QlBo aWxpcCBLYWx1ZGVyY2ljIChnZW5lcmF0ZWQgYnkgYXV0b2NyeXB0LmVsKSA8cGhpbGlwa0Bwb3N0 ZW8ubmV0PoiWBBMWCAA+FiEEDg7HY17ghYlni8XN8xYDWXahwukFAmQQUEICGwMFCQHhM4AFCwkI BwIGFQoJCAsCBBYCAwECHgECF4AACgkQ8xYDWXahwulikAEA77hloUiSrXgFkUVJhlKBpLCHUjA0 mWZ9j9w5d08+jVwBAK6c4iGP7j+/PhbkxaEKa4V3MzIl7zJkcNNjHCXmvFcEuDgEZBBQQhIKKwYB BAGXVQEFAQEHQI5NLiLRjZy3OfSt1dhCmFyn+fN/QKELUYQetiaoe+MMAwEIB4h+BBgWCAAmFiEE Dg7HY17ghYlni8XN8xYDWXahwukFAmQQUEICGwwFCQHhM4AACgkQ8xYDWXahwukm+wEA8cml4JpK NeAu65rg+auKrPOP6TP/4YWRCTIvuYDm0joBALw98AMz7/qMHvSCeU/hw9PL6u6R2EScxtpKnWof z4oM Received-SPF: pass client-ip=185.67.36.66; envelope-from=philipk@posteo.net; helo=mout02.posteo.de X-Spam_score_int: -43 X-Spam_score: -4.4 X-Spam_bar: ---- X-Spam_report: (-4.4 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_MED=-2.3, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: help-gnu-emacs@gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Users list for the GNU Emacs text editor List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org Original-Sender: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org Xref: news.gmane.io gmane.emacs.help:144664 Archived-At: Heime writes: > Sent with Proton Mail secure email. > > ------- Original Message ------- > On Monday, August 7th, 2023 at 11:46 PM, Yuri Khan wrote: > > >> On Mon, 7 Aug 2023 at 18:04, Heime heimeborgia@protonmail.com wrote: >>=20 >> > I have made a macro and know that they are supposed to return >> > expanded code for use. Still I cannot understand the need to >> > call "macroexpand". Should't the macro already perform the >> > expansion ? >>=20 >>=20 >> You should be posting small examples of code that you=E2=80=99re trying, >> otherwise, there is high chance people will either misunderstand you >> or just disregard your questions as ill-posed. >>=20 >> ---- >>=20 >> When you define a macro, you indeed write the definition similarly to >> a function that returns expanded code. >>=20 >> (defmacro foo (&rest body) >> `(bar ,@body)) When you evaluate a form that references a macro, >> Elisp will (1) expand the macro, and (2) evaluate the result of the >> expansion: (foo 'quux) =E2=87=92 Debugger entered--Lisp error: >> (void-function bar) On the other hand, calling =E2=80=98macroexpand=E2= =80=99 on a >> data representation of that form will just return the expansion >> result: (macroexpand '(foo 'quux)) =E2=87=92 (bar 'quux) In this example= , I >> did not bother to define =E2=80=98bar=E2=80=99, so Elisp assumes it woul= d be a >> function and complains at evaluation time. But I could further >> define =E2=80=98bar=E2=80=99 as a macro: (defmacro bar (&rest body)` (ba= z ,@body)) >>=20 >> In this case, evaluating the original form shows that Elisp expanded >> both macros =E2=80=98foo=E2=80=99 and =E2=80=98bar=E2=80=99, and then tr= ied to call the undefined >> function =E2=80=98baz=E2=80=99: >>=20 >> (foo 'quux) >> =E2=87=92 Debugger entered--Lisp error: (void-function baz) >>=20 >> Meanwhile, =E2=80=98macroexpand=E2=80=99 still just expands a single lev= el of macros: >>=20 >> (macroexpand '(foo 'quux)) >> =E2=87=92 (bar 'quux) >>=20 >> and you can invoke it repeatedly until you get to the fixed point: >>=20 >> (macroexpand (macroexpand '(foo 'quux))) >> =E2=87=92 (baz 'quux) >>=20 >> (macroexpand (macroexpand (macroexpand '(foo 'quux)))) >> =E2=87=92 (baz 'quux) > > Then macroexpand is useful for diagnostics to expand at one level only > at a time. Thusly, if I just want to get the expanded code produced by=20 > a macro, I can just do pp-to-string upon the object made by a macro. > > (defmacro adder (mopi mopj) > `(+ ,(cl-second mopi) ,(cl-third mopj))) > > (princ (pp-to-string '(adder (* 3 5) (* 5 7)) )) ^ don't do this If you quote an expression, it won't be evaluated or macro-expanded any further. You can sort-of think of a macro like a kind of inline function call. The evaluation would go along these lines: (princ (pp-to-string (adder (* 3 5) (* 5 7)))) will be transformed into this at macro-expansion time, and evaluation would do this: (princ (pp-to-string (+ (cl-second '(* 3 5)) (cl-third '(* 5 7))))) (princ (pp-to-string (+ 3 7))) (princ (pp-to-string 10)) (princ "10\n") "10\n" > I would not do > > (princ (pp-to-string (macroexpand '(adder (* 3 5) (* 5 7))) ))