Обсуждение: A bug in scan.l

There is a rule like this in scan.l<br /><br />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])<br
/><br/><br />I think this should be corrected to <br /><br /><br />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])<br
/><br/><br />I have replaced whitespace with space. This has to be done because whitespace allows comments. This would
causeconflict between some of the alternatives. I found this, while trying to make this rule work with LL(1). Just
thought,it might be useful.<br /><br />Thanks,<br />Gokul.<br /> 

Gokulakannan Somasundaram <gokul007@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

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
matchesthe 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.<br /> But do we need
toallow comments as part of unicode escapes?<br /><br />Thanks,<br />Gokul.<br /><br /><div class="gmail_quote">On Wed,
Sep2, 2009 at 8:37 AM, Tom Lane <span dir="ltr"><<a href="mailto:tgl@sss.pgh.pa.us">tgl@sss.pgh.pa.us</a>></span>
wrote:<br/><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex;
padding-left:1ex;"><div class="im">Gokulakannan Somasundaram <<a
href="mailto:gokul007@gmail.com">gokul007@gmail.com</a>>writes:<br /> > I have replaced whitespace with space.
Thishas to be done because<br /> > whitespace allows comments. This would cause conflict between some of the<br />
>alternatives. I found this, while trying to make this rule work with LL(1).<br /><br /></div>Um, if it's ambiguous,
whydoesn't flex complain?<br /><br />                        regards, tom lane<br /></blockquote></div><br /> 

Gokulakannan Somasundaram <gokul007@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