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Re: [xsl] Simple Map Expression Grammar definition in the XPath 3.0 Recommendation


Subject: Re: [xsl] Simple Map Expression Grammar definition in the XPath 3.0 Recommendation
From: "Michael Kay mike@xxxxxxxxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>
Date: Sat, 10 May 2014 19:44:32 -0000

This continues a long tradition of the way the XPath grammar is defined. For
example,  in XPath 1.0, we have

AdditiveExpr	   ::=   	MultiplicativeExpr
| AdditiveExpr '+' MultiplicativeExpr
| AdditiveExpr '-' MultiplicativeExpr

meaning that an AdditiveExpr does not necessarily contain a +/- operator, and
leading to messy phrases like:

"An EqualityExpr (that is not just a RelationalExpr) or a RelationalExpr (that
is not just an AdditiveExpr) is evaluated ..."

In my book I chose to refer to an AdditiveExpr than actually contains a +/-
operator as a "non-trivial AdditiveExpr"

In the XSLT 3.0 spec we have also had to address this problem when classifying
expressions for streamability: " expressions are classified according to the
most specific production rule that they match....", so 3*2 is classified as a
MultiplicativeExpr even though it is also a (trivial) instance of
AdditiveExpr.

Perhaps there is a better way of doing it, but it's certainly not an error.

Michael Kay
Saxonica

On 10 May 2014, at 19:29, Dimitre Novatchev dnovatchev@xxxxxxxxx
<xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx> wrote:

> The W3C XPath 3.0 Recommendation XPath 3.0 grammar defines Simple Map
> expression in this way
> (http://www.w3.org/TR/2014/REC-xpath-30-20140408/#id-map-operator):
>
> [34]   SimpleMapExpr   ::=   PathExpr ("!" PathExpr)*
>
> It follows from this rule that a SimpleMapExpr is, among other things,
> any PathExpr  -- because "*" means "zero or more".
>
> It seems rather weird to call an expression that doesn't contain any
> instance of the simple map operator, a "simple mapping expression".
>
> My guess is that the rule was meant as:
>
> [34]   SimpleMapExpr   ::=   PathExpr ("!" PathExpr)+
>
> According to this rule, a SimpleMapExpr should contain at least one
> instance of the simple map operator.
>
> Hope that this problem is acknowledged and the correction is included
> in the Errata.
>
> --
> Cheers,
> Dimitre Novatchev
> ---------------------------------------
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