[Monetdb-developers] XRPC syntax

p.a.boncz at chello.nl p.a.boncz at chello.nl
Fri Oct 27 12:39:48 CEST 2006

Hi Jens,

I had missed this email. The ambiguity you identify is for operators, which by default are built-ins. Thus, technically there is no ambiguity. 

In this case, you would parse "x eq y" as an ExprSingle, and then you will actually give a parse error because of the missing function application.

If it is really impossible to do (for some reason), I would propose the syntax:

XRPCCall ::= "execute" "at" ExprSingle "function" FunctionCall

which is analogous to DXQ: "execute" "at" ExprSingle "xquery" ExprSingle


> van: Jens Teubner <jens.teubner at in.tum.de>
> datum: 2006/10/24 Tue PM 02:55:21 MEST
> aan: Ying Zhang <Y.Zhang at cwi.nl>,  P.Boncz at cwi.nl
> onderwerp: XRPC syntax
> Hi Jennie, hi Peter,
> I am currently looking into the XRPC syntax.  Primarily I wanted to give
> you feedback to what you wrote in your Plan-X submission.
> So you are defining the syntax to be
>    XRPCCall ::= "execute" "at" URILiteral FunctionCall
> Lateron, however, you allow more than just a literal URI, but rather an
> XQuery expression.  So `URILiteral' is definitely wrong here.
> Once you changed this to, say, ExprSingle, you end up with ambiguity in
> your parser.  Consider
>    execute at "foo" eq ("bar")
> (I couldn't think of a better example ad hoc.)  What we have here is an
> ambiguity: we don't know whether `eq' is supposed to be a function call,
> or if it is the binary operator `eq', followed by another expression in
> parenthesis.
> So I will take the freedom to modify your syntax proposal and do it in a
> more XQuery-like style:
>    "execute" "at" "{" Expr "}" "{" FunctionCall "}"
> This avoids the ambiguity and should make it rather easy to parse.
> ...already hacking...
> Jens
> -- 
> Jens Teubner
> Technische Universitaet Muenchen, Department of Informatics
> D-85748 Garching, Germany
> Tel: +49 89 289-17259     Fax: +49 89 289-17263
> Time is money. Especially if you make clocks.

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