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Re: member inconsistency?

From: Stephen Berman
Subject: Re: member inconsistency?
Date: Thu, 28 Jan 2016 18:30:04 +0100
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/25.0.50 (gnu/linux)

On Thu, 28 Jan 2016 17:48:29 +0200 Eli Zaretskii <address@hidden> wrote:

>> From: Stephen Berman <address@hidden>
>> Date: Thu, 28 Jan 2016 11:25:33 +0100
>> Cc: Philipp Stephani <address@hidden>,
>>      Nicolas Goaziou <address@hidden>, address@hidden
>> In contrast, `member' (and `memql' in the float case) has no check
>> and also uses a for-loop with the condition CONSP (tail), and when
>> this fails, the function just returns Qnil.  Adding CHECK_LIST
>> (list) before the for-loop makes (member 'a 'b) signal an error.
> I'd say CHECK_LIST_CONS, not CHECK_LIST, don't you agree?

To be honest, I overlooked that CHECK_LIST_CONS is inside the for-loop.
But it seems a bit ugly to have the same check before the loop and
inside it as well.  How about the following:

diff --git a/src/fns.c b/src/fns.c
index 86ad333..17c4a75 100644
--- a/src/fns.c
+++ b/src/fns.c
@@ -1349,7 +1349,7 @@ The value is actually the tail of LIST whose car is ELT.  
   (register Lisp_Object elt, Lisp_Object list)
   register Lisp_Object tail;
-  for (tail = list; CONSP (tail); tail = XCDR (tail))
+  for (tail = list; CONSP (tail) || !NILP (tail); tail = XCDR (tail))
       register Lisp_Object tem;
       CHECK_LIST_CONS (tail, list);

Or is having the check before the loop better it catches the error sooner?

Steve Berman

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