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RE: [XQuery] Comment - Pragma/MUExtension confusion

From: Kirmse, Daniel <daniel.kirmse@sap.com>
Date: Thu, 2 Sep 2004 08:42:01 +0200
Message-ID: <9A33D7528D46DF47B0C0630618F3E68461CCB2@dewdfe12.wdf.sap.corp>
To: "'scott_boag@us.ibm.com'" <scott_boag@us.ibm.com>
Cc: "'public-qt-comments@w3.org'" <public-qt-comments@w3.org>

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 06:42:46 UTC

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