bug#48315: (ice-9 match) does not suport #nil
Taylan Kammer <[email protected]>
| Newsgroups | gmane.lisp.guile.bugs |
|---|---|
| Message-ID | <[email protected]> |
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, 1.4 KB)
From b6d0b715a8bf0cc39b9fc3d46efeaf010f0d4351 Mon Sep 17 00:00:00 2001 From: Taylan Kammer <[email protected]> Date: Wed, 12 May 2021 21:46:54 +0200 Subject: [PATCH] Fix match when used directly on the #nil constant. * module/ice-9/match.upstream.scm (match): Make sure we don't match #nil where we don't intend to. Fixes <https://bugs.gnu.org/48315>. --- module/ice-9/match.upstream.scm | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/module/ice-9/match.upstream.scm b/module/ice-9/match.upstream.scm index b1fc371b8..3b181b75b 100644 --- a/module/ice-9/match.upstream.scm +++ b/module/ice-9/match.upstream.scm @@ -269,9 +269,12 @@ (match-syntax-error "missing match expression")) ((match atom) (match-syntax-error "no match clauses")) - ((match (app ...) (pat . body) ...) - (let ((v (app ...))) - (match-next v ((app ...) (set! (app ...))) (pat . body) ...))) + ;; The original implementation uses (app ...) not (op arg ...) here, + ;; but in Guile this would match #nil when it shouldn't. Failing to + ;; match () doesn't matter since it leads to an error anyway. + ((match (op arg ...) (pat . body) ...) + (let ((v (op arg ...))) + (match-next v ((op arg ...) (set! (op arg ...))) (pat . body) ...))) ((match #(vec ...) (pat . body) ...) (let ((v #(vec ...))) (match-next v (v (set! v)) (pat . body) ...))) -- 2.30.2