[Xcb] XML-XCB: language-neutral bit constants

[Jamey Sharp]

On Tue, Mar 14, 2006 at 11:23:46AM -0800, Ian Osgood wrote:
> On Tue, 14 Mar 2006, Ian Osgood wrote:
> >> We should strive to be language-neutral in the protocol
> >> definitions, right?

Certainly...

> >> <op="&lt;&lt;"> is 1) ugly 2) repetitious

No argument there.

> >> 3) C-specific.
> 
> <bit> is for addressing a bit in a word.  The C idiom is (1<<n), but
> other languages name this "shl(1,n)" or have built in bit addressing
> syntax (Pascal, Modula, and Oberon's sets for instance).

But I don't think I agree with this. It's not hard to pattern-match
these cases in the existing XML. An XPath expression something like this
should do it (though my XPath is rusty):

op[@op="&lt;&lt;" and value[1]="1"]/value[2]

That said, your other two reasons are probably sufficient.

> >I came up with <bit bit="n"/>, which replaces:
> >
> ><op op="&lt;&lt;"><value>1</value><value>n</value></op>
> >
> >Unless there are objections, I'll push my changes to xproto.xml,
> >xcb.xsd, and c-client.xsl.

I assume your changes to xproto.xml involve demonstrating how to use
<bit>? It'd be good to commit that after committing the xsl/xsd changes.

> I'm adding a convenience function for one usage of the op="&lt;&lt;"
> tag (see above).   <op> itself is unmodified.  I realize that
> changing the name of operators &amp; and &lt;&lt; would result in
> lots of breakage in the extensions.

If there's a strong argument for changing the operator names, we can
accept multiple names for the same operator, to provide time for a
transition.

--Jamey
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