Re: What should /\08/ match and do?

karl williamson wrote:
> Abigail wrote:
>> On Fri, Jun 04, 2010 at 07:45:36AM -0600, karl williamson wrote:
>>> Abigail wrote:
>>>
>>> OK.  What about '\0a'  It doesn't warn currently.  It is analogous 
>>> to  \08 but has a non-octal hex digit instead of a non-octal decimal 
>>> digit.  Should it warn?
>>
>>
>> IMO, no. It doesn't now, and it's too easy to generate false warnings.
>> I also think it's very less likely to make a hexadecimal-instead-of-octal
>> error, then a digital-instead-of-octal error. After all, for most people
>> digital is what they've learned early in life. As Nick said, warning on
>> \08 makes sense, as it may happen because someone added 1 to \07, 
>> forgetting
>> about the octal issue.
>> Heck, we don't even warn (and we shouldn't start now, I may add) on 
>> /\xabc/.
>>
>>
>> Abigail
>>
> 
> OK.  I think we have agreement.  I'll recap to give people another 
> chance to disagree, but first, am I overlooking something if I change 
> the docs to say that using 3 digits always for \OOO causes the 
> ambiguities to completely go away, including concatenation of strings to 
> form larger patterns, as long as there are fewer than 64 (= \100) 
> capture groups?
Never mind on this.  I hit send a little too soon.  Just a little more 
thought brought out what perhaps should have been more obvious: begin 
your numbers with 0 and they won't be considered backreferences; but 
what you think might be backreferences can turn into octal characters by 
concatenation.
> 
> So here's what I'm planning:
> 
> Existing Behavior Changes
>   [\8\9] will mean [89] instead of [89\000].     
>   The current wrong warning "Illegal octal digit
>   ignored" will change to "Unrecognized escape"
> 
>   \400 and above in one context now generates a
>   deprecated message and is taken modulo \400.
>   It wil will now mean \x{100} and above, with
>   no warning.  This matches behavior in all other
>   places except -0 on the command line.
> 
>   \o{...} will now generate an octal constant
>   instead of the literal o{...} and the
>   "Unrecognized escape" warning on the 'o'
> 
>   \o not followed by a { will now be a syntax
>   error instead of "Unrecognized escape" warning
>   on the 'o'
> 
> Additional warning message changes
>   \08 \009 will generate a new message instead of
>   the existing wrong "Illegal octal digit ignored".
>   I'm thinking: "Too few digits in octal character
>   constant; assuming you meant '\\%04d'".
> 
> Documentation will be updated, including saying that -0400 and above on 
> the command line means the same as -0777 currently does.
>