From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Vivien Kraus Newsgroups: gmane.lisp.guile.user Subject: Control the order of expansion of syntax-case macros Date: Tue, 17 Dec 2024 17:33:04 +0100 Message-ID: <1bfa042ed3719a10006789205e954bb53c83cf45.camel@planete-kraus.eu> 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="27483"; mail-complaints-to="usenet@ciao.gmane.io" User-Agent: Evolution 3.48.4 To: Guile User Original-X-From: guile-user-bounces+guile-user=m.gmane-mx.org@gnu.org Tue Dec 17 17:33:52 2024 Return-path: Envelope-to: guile-user@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 1tNaW8-00071o-0f for guile-user@m.gmane-mx.org; Tue, 17 Dec 2024 17:33:52 +0100 Original-Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1tNaVj-0007JR-Kl; Tue, 17 Dec 2024 11:33:27 -0500 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 1tNaVe-0007Is-Lp for guile-user@gnu.org; Tue, 17 Dec 2024 11:33:23 -0500 Original-Received: from planete-kraus.eu ([2a00:5881:4008:2810::309]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_CHACHA20_POLY1305:256) (Exim 4.90_1) (envelope-from ) id 1tNaVZ-0007bJ-0s for guile-user@gnu.org; Tue, 17 Dec 2024 11:33:22 -0500 Original-Received: from planete-kraus.eu (localhost.lan [127.0.0.1]) by planete-kraus.eu (OpenSMTPD) with ESMTP id fe266045 for ; Tue, 17 Dec 2024 16:33:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha1; c=relaxed; d=planete-kraus.eu; h= message-id:subject:from:to:date:content-type :content-transfer-encoding:mime-version; s=albinoniB; bh=+0yi9Df htwqM98KjZAkodvHU3bw=; b=bvxGwHcvYRnNVqsM9yQ4zJeR35t6LySvZla5/A6 bjK/qJAwHvBJPVxNoJOE4Ys6vEtSPObgbYZx7bFxYB5RMTXK7/TKGBBmxtNQ5CKS +LiumdzJ8tlSMGtHxHow3CuiOkd4KSDIjtHJW56Edr4SfsplSDTeDgWL15xXT09q VnU+/Cf397q2S0n8bhDtG/8Me81OFF7+wkwAITJSqdvbjzAciCfSPyxvIGt+1yeP t/8+Tl9X+sVVv9D0AGSLsdZlY4h/VMkJBPe759EUgFDcX7/eXCGOht2O1smSpXak M3j7WHcnfx/n5wYJdrUr5nefKOYXuZSlwYQvdnzuPAJCngg== Original-Received: by planete-kraus.eu (OpenSMTPD) with ESMTPSA id bc753d41 (TLSv1.3:TLS_CHACHA20_POLY1305_SHA256:256:NO) for ; Tue, 17 Dec 2024 16:33:06 +0000 (UTC) Received-SPF: pass client-ip=2a00:5881:4008:2810::309; envelope-from=vivien@planete-kraus.eu; helo=planete-kraus.eu X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 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, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: guile-user@gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: General Guile related discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: guile-user-bounces+guile-user=m.gmane-mx.org@gnu.org Original-Sender: guile-user-bounces+guile-user=m.gmane-mx.org@gnu.org Xref: news.gmane.io gmane.lisp.guile.user:20011 Archived-At: Dear Guile users, syntax-case macros can have cool side effects at expansion time. However, they are still draped in a veil of mystery to me. Consider this code: (define-syntax hello (lambda (stx) (syntax-case stx () (_ (begin (format (current-error-port) "Hello!\n") (datum->syntax #f "hello")))))) (define-syntax world (lambda (stx) (syntax-case stx () (_ (begin (format (current-error-port) "World!\n") (datum->syntax #f "world")))))) (define-syntax hello-world (lambda (stx) (syntax-case stx () (_ #`(string-append #,hello " " #,world))))) ,expand hello-world Running it gives me: Hello! World! $1 =3D (string-append "hello" " " "world") Cool! Now, I suspect there are no clear rules to guess the order of expansion (whether Hello! is printed before World! or after). I would very much like to twist that order and reliably get World! and then Hello!. How can I achieve that? (define-syntax hello-world (lambda (stx) (syntax-case stx () (_ (let* ((w #'world) (h #'hello)) #`(string-append #,h " " #,w)))))) With this modification, I get the same order: Hello! World! $1 =3D (string-append "hello" " " "world") So my guess is that syntax objects are expanded lazily. Is there something I can do to get #'world expanded before #'hello? Best regards, Vivien