W3C home > Mailing lists > Public > public-rdf-dawg@w3.org > July to September 2005

Re: Possible grammar bug with PrimaryExpression and ArgList

From: Seaborne, Andy <andy.seaborne@hp.com>
Date: Wed, 10 Aug 2005 17:52:02 +0100
Message-ID: <42FA30B2.3060005@hp.com>
To: Dave Beckett <dave.beckett@bristol.ac.uk>
CC: DAWG public list <public-rdf-dawg@w3.org>



Dave Beckett wrote:
> I was wondering what changed as in the current rq23 ArgList is optional
> for function calls and this seemed like a syntax change.  This took a
> little digging into the record so I'm recording what I found.

Thanks for doing that.  Something seems to have gone amiss.

> 
> I finally tracked it down to rq23 between CVS 1.451 and 1.452:
> [[
> Revision 1.452  2005/08/04 10:57:36  aseaborne
> + Added "_" to start of variable names
> ~ Tidied up by intrpducing NCCHAR1p and making NCCHAR1 be NCCHAR1p | '_'
> ]]
> 
> (for reference the last WD was around 1.432).
> 
> This change seems to do a bit more than that:
> * FunctionCall is removed from Constraint

v1.463 says:

[25] Constraint ::= 'FILTER' ( BrackettedExpression | BuiltInCall | FunctionCall )
[55] FunctionCall ::= IRIref ArgList

[56] ArgList ::= ( '(' ')' | '(' Expression ( ',' Expression )* ')' )

The argument list is not optional for a function call at this point.

The formatting for BuiltInCall could be better.

Eric had some suggestions from using flex/bison related to the double meaning of 
() as an empty argument list and as rdf:nil.  This was addressed by inlining 
explicitly the () cases, not having an explicit rule suggesting a unique 
tokenization.

> * ConstructTemplate uses ConstructTriples for it's inner content

I thought this had happened a while ago - must have had a synchronization error.

In support of yacc, Eric made various suggestions that made it easier for him 
(and I presumed all bison/flex LALR(1) setups) as well as made the grammar more 
LL(1).

> * ConstructTriples added with content from above.
> * GraphTerm inlines the RDFTerm token and adds '(' ')' (empty
> collection)

Removed a rule that was used only once.  Again, sometime ago and there has been 
a sync error.  Apologies.

> * BuiltInCall renamed from CallExpression and FunctionCall is removed as
> an option.
> * PrimaryExpression:
>     CallExpression renamed to BuiltInCall
>     Adds IRIref ArgList?

Result of the discussion about resolving the ambiguity of qname vs function.
"IRIref ArgList?" covers both cases.

Example:

   FILTER ( ?x = ex:p )		 # ex:p is a qname

   FILTER ( ?x = ex:f(?a, ?b) )   # ex:f is a function call

http://www.w3.org/2005/06/14-dawg-irc

Worrying mistake somewhere after that.


>     Adds RDFLiteral | NumericLiteral | BooleanLiteral | BlankNode | Var
> 
> Most of that is tidying or reasonable change but the addition that is
> the problem is IRIref ArgList? which is not the same as FunctionCall:
> IRIref ArgList which I'm guessing it was intended to be.
> 
> If you want a test:
> 
> PREFIX my: <http://example.org/>
> SELECT *
> WHERE {
>   ?s ?p ?o .
>   FILTER my:function
> }
> 
> is legal according to my reading of rq23 whereas it used to be illegal.

FILTER with no brackets follows rule 55 which does not allow omission of the 
argument list.

> 
> I assume the additional '?' is a mistake or have I missed something?
> Maybe just using FunctionCall instead would be easier.

At that point it does. It's the other way of getting there that has the ambiguity.

> 
> Dave


	Again, thanks
	Andy
Received on Wednesday, 10 August 2005 16:52:33 GMT

This archive was generated by hypermail 2.3.1 : Tuesday, 26 March 2013 16:15:24 GMT