GNU bug report logs - #48315
(ice-9 match) does not suport #nil

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Maxime Devos <maximedevos <at> telenet.be>
To: bug-guile <at> gnu.org
Subject: (ice-9 match) does not suport #nil
Date: Sun, 09 May 2021 17:57:41 +0200

[Message part 1 (text/plain, inline)]

guile --version:
guile (GNU Guile) 3.0.5

(use-modules (ice-9 match))

(match #nil (_ 'xyzzy))
-->
While compiling expression:
Syntax error:
unknown location: unexpected syntax in form ()

(match '() (_ 'xyzzy))
--> $16 = xyzzy

Greetings,
Maxime.

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Message #8 received at 48315 <at> debbugs.gnu.org (full text, mbox):

From: Taylan Kammer <taylan.kammer <at> gmail.com>
To: 48315 <at> debbugs.gnu.org
Subject: (ice-9 match) does not suport #nil
Date: Wed, 12 May 2021 22:03:57 +0200

[Message part 1 (text/plain, inline)]

This was mind-boggling to debug!

In syntax-rules, the pattern (x ...) will match #nil, since it
matches the empty list.  This can have surprising consequences.

Consider:

  (define-syntax test
    (syntax-rules ()
      ((test (x ...))
       (x ...))
      ((test x)
       x)))

  (test (+ 1 2))  ; => 3
  (test 123)      ; => 123
  (test #f)       ; => #f
  ;; However...
  (test #nil)     ; error


Anyway, attached is a patch to fix the issue in match.


- Taylan

[0001-Fix-match-when-used-directly-on-the-nil-constant.patch (text/plain, attachment)]

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