Re: error in replace-match: "args out of range"

[PJ Weisberg]

On 4/9/11, David Kastrup <dak@gnu.org> wrote:
> ken <gebser@mousecar.com> writes:
>
>> On 04/09/2011 02:44 AM PJ Weisberg wrote:
>>> On 4/8/11, ken <gebser@mousecar.com> wrote:
>>>> On 04/07/2011 07:25 PM Tim X wrote:
>>>>> This was my point of warning. It is quite possible to have
>>>>> regexps where sub expressions are not found, but the overall regexp
>>>>> succeeds.
>>>> I'm having a hard time with that concept.  Is there a small bit of
>>>> example code you could show it with?
>>>
>>> "I am\\( not\\)? a fish."
>>>
>>> -PJ
>>
>> And on what sort of string would that RE match but the subexpression
>> have the value nil (as opposed to the null string "")?
>
> Huh?  Isn't that rather obvious?
>
> (list (string-match "I am\\( not\\)? a fish." "I am a fish!")
>       (match-string 1)) => (0 nil)

Notice that the expression " not" can NEVER match an empty string.
The ? allows it to appear zero times, so the overall expression
matches even though the subexpression doesn't.

-PJ