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 20:08:29 +0000 Message-ID: <87sf8usjia.fsf@posteo.net> References: <87wmy7rkxp.fsf@posteo.net> <2cUOv53USl65TgeJJfJlgDmgfzHuXV-aVXANzNsUzvHYoGAwJS2QxesnnSrbkuath2yoan9_Ws8P37dXBRVIFdGgTkFb5rZuG5WyxnqSXv0=@protonmail.com> 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="15172"; 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 22:09:26 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 1qT6Xc-0003hW-6Y for geh-help-gnu-emacs@m.gmane-mx.org; 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envelope-from=philipk@posteo.net; helo=mout01.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:144669 Archived-At: Heime writes: > Sent with Proton Mail secure email. > > ------- Original Message ------- > On Tuesday, August 8th, 2023 at 2:22 AM, Philip Kaludercic wrote: > > >> Heime heimeborgia@protonmail.com writes: >>=20 >> > Sent with Proton Mail secure email. >> >=20 >> > ------- Original Message ------- >> > On Monday, August 7th, 2023 at 11:46 PM, Yuri Khan yuri.v.khan@gmail.c= om wrote: >> >=20 >> > > 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 >> > > You should be posting small examples of code that you=E2=80=99re try= ing, >> > > 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 E= lisp assumes >> > > it would 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)` (baz ,@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 the= n tried 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= level 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) >> >=20 >> > 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 >> > a macro, I can just do pp-to-string upon the object made by a macro. >> >=20 >> > (defmacro adder (mopi mopj) >> > `(+ ,(cl-second mopi) ,(cl-third mopj))) >> >=20 >> > (princ (pp-to-string '(adder (* 3 5) (* 5 7)) )) >>=20 >> ^ >> don't do this >>=20 >> 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: >>=20 >> (princ (pp-to-string (adder (* 3 5) (* 5 7)))) >>=20 >> will be transformed into this at macro-expansion time, and evaluation >> would do this: >>=20 >> (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" > > What I want to do is print the code made by adder of its final expansion = code. > Rather than the last evaluation of 10, I want to print (+ 3 7).=20=20 > > Can my print command be modified in such a way that the message shows (+ = 3 7) ? > IT seems that I would need to use macroexpand-all, to get to the final un= evaluated > sexp.=20 You can modify your macro, to return a quoted expression. (defmacro adder (mopi mopj) `'(+ ,(cl-second mopi) ,(cl-third mopj))) ^ note this This is synonymous with (defmacro adder (mopi mopj) (list 'quote (list '+ (cl-second mopi) (cl-third mopj)))) which makes sense, if you keep in mind that the result of evaluating the macro is what replaces the macro expression in the syntax tree. >> > I would not do >> >=20 >> > (princ (pp-to-string (macroexpand '(adder (* 3 5) (* 5 7))) ))