bug#65132: [PATCH] fix cond1 macro

bug#65132: [PATCH] fix cond1 macro

[Ekaitz Zarraga]

From ab6e4980ea301b5d1e14a98464e5de3e726984f1 Mon Sep 17 00:00:00 2001
From: Ekaitz Zarraga <ekaitz@elenq.tech>
Date: Mon, 7 Aug 2023 20:23:42 +0200
Subject: [PATCH] fix cond1 macro

* doc/ref/api-macros.texi (Macros): Fix doc1 macro example
---
 doc/ref/api-macros.texi | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/doc/ref/api-macros.texi b/doc/ref/api-macros.texi
index 7fdf578c7..f13ac0136 100644
--- a/doc/ref/api-macros.texi
+++ b/doc/ref/api-macros.texi
@@ -229,10 +229,10 @@ Literals are used to match specific datums in an expression, like the use of
     ((cond1 test => fun)
      (let ((exp test))
        (if exp (fun exp) #f)))
-    ((cond1 test exp exp* ...)
-     (if test (begin exp exp* ...)))
     ((cond1 else exp exp* ...)
-     (begin exp exp* ...))))
+     (begin exp exp* ...))
+    ((cond1 test exp exp* ...)
+     (if test (begin exp exp* ...)))))
 
 (define (square x) (* x x))
 (cond1 10 => square)
-- 
2.41.0

bug#65132: [PATCH] fix cond1 macro

[Timothy Sample]

Hi all,

Ekaitz Zarraga <ekaitz@elenq.tech> writes:

> From ab6e4980ea301b5d1e14a98464e5de3e726984f1 Mon Sep 17 00:00:00 2001
> From: Ekaitz Zarraga <ekaitz@elenq.tech>
> Date: Mon, 7 Aug 2023 20:23:42 +0200
> Subject: [PATCH] fix cond1 macro

Just adding some context, as we talked about this on IRC.

If you take the docs example as is,

    (define-syntax cond1
      (syntax-rules (=> else)
        ((cond1 test => fun)
         (let ((exp test))
           (if exp (fun exp) #f)))
        ((cond1 test exp exp* ...)
         (if test (begin exp exp* ...)))
        ((cond1 else exp exp* ...)
         (begin exp exp* ...))))

and invoke it as

    (cond1 else #t)

you get

    Syntax error:
    unknown location: else: bad use of 'else' syntactic keyword in
    subform else of else

This is because ‘else’ matches the ‘(cond1 test exp exp* ...)’ pattern
and gets inserted as the test:

    (if else (begin #t))

This patch puts the more specific ‘else’ pattern before the more general
‘test’ pattern so it has a chance to be matched.


-- Tim

bug#65132: ...

[lloda]

Patch applied in 1e3b5390e3c24e66013118e9751db4de5025a4a2.

Thanks,

  Daniel