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RE: [XQuery] Comment - Pragma/MUExtension confusion

From: <scott_boag@us.ibm.com>
Date: Thu, 2 Sep 2004 11:07:28 -0400
To: "Kirmse, Daniel" <daniel.kirmse@sap.com>
Cc: "'public-qt-comments@w3.org'" <public-qt-comments@w3.org>
Message-ID: <OFD2C95E22.DC2ABF59-ON85256F03.0051E509-85256F03.005314F5@lotus.com>

That's more than a cosmetic change, and would disallow things like 
"(:?:)", which are perfectly reasonable.  Maybe:

[151]           Comment    ::=          "(:" (CommentContents | Comment)+ 
":)"

Then restrict CommentContents from having ":" as the first character. 

[152]           CommentContents    ::=          (Char - ':') (Char+ - 
(Char* ':)' Char*))

...is the medicine worse than the ailment?

-scott

"Kirmse, Daniel" <daniel.kirmse@sap.com> wrote on 09/02/2004 02:42:01 AM:

> Hi Scott,
> 
> lookahead wasn't realy an issue in that. It's more about ambiguity 
> of productions. However, considering this longest possible match 
> rule the issue could be covered from a parsers point of view. I'll 
> follow this rule for my implementation.
> The concerns still remain, though. Because from a users point of 
> view even (::) would be a perfectly correct comment according to 
> grammar production [149]. So my confusion arose from that. Looks 
> like [149] rather should be like this:
> 
> [149] Comment :== "(:" S (CommentContents | Comment)* ":)" /* 
ws:explicit */
> 
> To avoid this kind of confusion.
> 
> Cheers,
> Daniel
> 
> -----Original Message-----
> From: public-qt-comments-request@w3.org [mailto:public-qt-comments-
> request@w3.org] On Behalf Of scott_boag@us.ibm.com
> Sent: Mittwoch, 1. September 2004 20:26
> To: Kirmse, Daniel
> Cc: 'public-qt-comments@w3.org'
> Subject: Re: [XQuery] Comment - Pragma/MUExtension confusion
> 
> 
> Hi Daniel.  Please bear with me, as I'm not 100% sure I understand your 
> issue.
> 
> I would think the longest token rule covers your examples.  "When 
> tokenizing, the longest possible match that is valid in the current 
> lexical state is preferred ."  (A.2 Lexical structure).   So:
> 
>  "(: :)"   ...is a valid comment
> "(::)"      ...is not valid (ill-formed pragma or extension)
> "(: ::)"   ...is a valid comment (with a space and ":" char within it)
> "(:: :)"   ...is not valid (ill-formed pragma or extension)
> "(::::)"   ...is not valid (ill-formed pragma or extension)
> "(:::)"    ...is not valid (ill-formed pragma or extension)
> 
> No look-ahead should be required.
> 
> Please let me know if I've addressed your issue, or misunderstood it.
> 
> -scott
> 
> public-qt-comments-request@w3.org wrote on 09/01/2004 04:59:55 AM:
> 
> > Hi,
> > I found a disturbing thing in the XQuery grammar. Consider these 
> productions:
> > [146]    Pragma    ::=    "(::" S? "pragma" S QName (S 
> > ExtensionContents)? "::)" /* ws: explicit */ 
> > [147]    MUExtension    ::=    "(::" S? "extension" S QName (S 
> > ExtensionContents)? "::)" /* ws: explicit */ 
> > [148]    ExtensionContents    ::=    (Char* - (Char* '::)' Char*)) 
> > [149]    Comment    ::=    "(:" (CommentContents | Comment)* ":)" /*
> > ws: explicit */ 
> >     /* gn: comments */ 
> > [150]    CommentContents    ::=    (Char+ - (Char* ':)' Char*))
> > The XQuery Expression "(: :)" is a valid comment, even so the 
> > expression (::) because no whitespace is required by production 
> > [149]. The example parser on http://www.w3.
> > org/2004/08/applets/xqueryApplet.html however returns an "Lexical 
> > error at line 1, column 4.  Encountered: ")" (41), after : """. 
> > Obviously it thinks to have found the begin of a Pragma or 
MUExtension.
> > The expression "(::::)" is as valid a comment as "(:::)". To be honest 
I 
> 
> > claim each Pragma or MUExtension would make up a valid comment as long 

> as 
> > ":)" is not part of it. First I thought it would be a case of 
> > lookahead 1 vs. lookahead 2. But no. It rather looks like a serious 
> > problem that no lookahead possibly could resolve. As long as a ":" 
> > is a valid character inside a comment (only the sequence ":)" is 
> > forbidden) only a human being could tell a comment from a Pragma or 
> > MUExtension. 
> > Either there is a serious problem in the grammar or I made myself a 
> > complete idiot. I'm not sure which would relief me more.
> > What is the resolution of this?
> > Cheers,
> > Daniel
Received on Thursday, 2 September 2004 15:08:07 UTC

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