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

On Sat, Jun 05, 2010 at 08:58:12AM -0600, 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?
>
> So here's what I'm planning:
>
> Existing Behavior Changes
>   [\8\9] will mean [89] instead of [89\000].  	

That sounds like a bug fix. Bug fixes are good.

>   The current wrong warning "Illegal octal digit
>   ignored" will change to "Unrecognized escape"

For just \8 and \9 I presume? Or also for /\18/? It's not an unrecognized
escape if it keeps its existing meaning of /\x{1}8/ (assuming no 18 set
of preceeding capturing parenthesis.

>   \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.

Does this mean that chr (03000) =~ /\3000/, and that no longer (chr
(0300) . "0") =~ /\3000/? I've no problem with this change in behaviour
(I'd say that's what many people will expect in a post ASCII/LATIN-1
world), but /\3000/ does not currently warn. Or are you just talking
about \400 .. \777 ?


>   \o{...} will now generate an octal constant
>   instead of the literal o{...} and the
>   "Unrecognized escape" warning on the 'o'

+1

>   \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'".

Ah, that probably answers my question above. But too few digits? If one
changes the 8 and the 9 to X and Y, it won't complain about the number 
of digits.

> Documentation will be updated, including saying that -0400 and above on  
> the command line means the same as -0777 currently does.


I also assume that, where appropriate, these changes are for all
interpolative contexts, not just m//, s///, and qr//?


Abigail