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Message-ID:  <55E09AA8.6070100@residenset.net>
Date:         Fri, 28 Aug 2015 19:30:16 +0200
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From: =?UTF-8?B?TGFycyBIZWxsc3Ryw7Zt?= <Lars.Hellstrom@RESIDENSET.NET>
Subject: Re: Catcode changes
To: LATEX-L@LISTSERV.UNI-HEIDELBERG.DE
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Status: R

Joseph Wright skrev 2015-08-27 22.18:
> On 27/08/2015 19:09, Joseph Wright wrote:
>> On 27/08/2015 18:28, Lars Hellström wrote:
>>> Bruno Le Floch skrev 2015-08-27 12.34:
>>>> That's much harder.  Catcode changes are probably warranted in this
>>>> case, since teaching TeX to nest parentheses in this way is tough.
>>>
>>> I seem to recall that I did demonstrate how to do that -- have TeX match
>>> parentheses in an expression, using delimited arguments rather than
>>> catcode changes -- in a mail to this very list several years ago... Yes,
>>> it was on 2011-10-19 and the subject was "Re: Church booleans".
>>
>> We do the same in xparse :-)

Are you saying xparse handles _matching_ of _nested_ parentheses? Because 
that is what I meant that I demonstrated. Using delimited arguments to grab 
parentheses without considering how they match against each other is of 
course a triviality, but also not useful for the problem considered.

>>> PS: I maintain that that approach to evaluating infix boolean
>>> expressions is far superior to what is currently offered in LaTeX3, but
>>> Bruno just seems to *love* his&&, with all its shortcomings. ;-)
>>
>> Will remind myself: as has been noted there is an issue with clearing up
>> certain tokens with the current lazy evaluation method.

More fundamentally, I believe it only supports expandable tests. There is no 
need for a boolean evaluation logic to require tests to be expandable (and 
nor does the logic itself need to be non-expandable).

>> Joseph
>>
>
> BTW, thread you mean starts
>
>    http://article.gmane.org/gmane.comp.tex.latex.latex3/2719
>
> I think the one you mean is
>
>    http://article.gmane.org/gmane.comp.tex.latex.latex3/2754

Ah, that is correct.

> Joseph
>
> P.S. Boolean expressions are Morten's code, not Bruno's :-)

Oh? I seem to recall Bruno posted repeatedly on it this summer, giving the 
appearance that he was actively working on precisely that code. My bad, in 
that case.

Lars Hellström