Re: [HACKERS] A bug in scan.l

2009-09-02 Thread Tom Lane 
Gokulakannan Somasundaram gokul...@gmail.com writes:
 Well, i am at a very beginner level with Flex. I could see how flex works
 with it even if it is a ambiguity. Since it matches the rule with the
 maximum text and we don't allow a new line character in the rule, it works
 fine.  Even in LL(1), it works fine, but throws warnings. So i just thought
 of suggesting to remove the ambiguity.

Well, that whole rule is only there for implementation-specific reasons
--- a flex scanner is faster if it doesn't need to back up.  You might
be best off to just remove the anti-backup rules in the LL translation.

 But do we need to allow comments as part of unicode escapes?

If they're like normal strings, yes.

regression=# select 'this is' -- comment
regression-# ' one string';
  ?column?  

 this is one string
(1 row)

Don't blame us, blame the SQL committee.  This was not one of their
better ideas IMO.

regards, tom lane

-- 
Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-hackers

Re: [HACKERS] A bug in scan.l

2009-09-01 Thread Gokulakannan Somasundaram 
The previous change should follow with this.

uescape[uU][eE][sS][cC][aA][pP][eE]{space}*{quote}[^']{quote}

Thanks,
Gokul.

On Wed, Sep 2, 2009 at 7:35 AM, Gokulakannan Somasundaram 
gokul...@gmail.com wrote:

 There is a rule like this in scan.l

 uescapefail
 (-|[uU][eE][sS][cC][aA][pP][eE]{whitespace}*-|[uU][eE][sS][cC][aA][pP][eE]{whitespace}*{quote}[^']|[uU][eE][sS][cC][aA][pP][eE]{whitespace}*{quote}|[uU][eE][sS][cC][aA][pP][eE]{whitespace}*|[uU][eE][sS][cC][aA][pP]|[uU][eE][sS][cC][aA]|[uU][eE][sS][cC]|[uU][eE][sS]|[uU][eE]|[uU])


 I think this should be corrected to


 uescapefail
 (-|[uU][eE][sS][cC][aA][pP][eE]{space}*-|[uU][eE][sS][cC][aA][pP][eE]{space}*{quote}[^']|[uU][eE][sS][cC][aA][pP][eE]{space}*{quote}|[uU][eE][sS][cC][aA][pP][eE]{space}*|[uU][eE][sS][cC][aA][pP]|[uU][eE][sS][cC][aA]|[uU][eE][sS][cC]|[uU][eE][sS]|[uU][eE]|[uU])


 I have replaced whitespace with space. This has to be done because
 whitespace allows comments. This would cause conflict between some of the
 alternatives. I found this, while trying to make this rule work with LL(1).
 Just thought, it might be useful.

 Thanks,
 Gokul.

Re: [HACKERS] A bug in scan.l

2009-09-01 Thread Tom Lane 
Gokulakannan Somasundaram gokul...@gmail.com writes:
 I have replaced whitespace with space. This has to be done because
 whitespace allows comments. This would cause conflict between some of the
 alternatives. I found this, while trying to make this rule work with LL(1).

Um, if it's ambiguous, why doesn't flex complain?

regards, tom lane

-- 
Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-hackers

Re: [HACKERS] A bug in scan.l

2009-09-01 Thread Gokulakannan Somasundaram 
Well, i am at a very beginner level with Flex. I could see how flex works
with it even if it is a ambiguity. Since it matches the rule with the
maximum text and we don't allow a new line character in the rule, it works
fine.  Even in LL(1), it works fine, but throws warnings. So i just thought
of suggesting to remove the ambiguity.
But do we need to allow comments as part of unicode escapes?

Thanks,
Gokul.

On Wed, Sep 2, 2009 at 8:37 AM, Tom Lane t...@sss.pgh.pa.us wrote:

 Gokulakannan Somasundaram gokul...@gmail.com writes:
  I have replaced whitespace with space. This has to be done because
  whitespace allows comments. This would cause conflict between some of the
  alternatives. I found this, while trying to make this rule work with
 LL(1).

 Um, if it's ambiguous, why doesn't flex complain?

regards, tom lane