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Message-ID:  <55DF5276.7010500@morningstar2.co.uk>
Date:         Thu, 27 Aug 2015 19:09:58 +0100
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From: Joseph Wright <joseph.wright@MORNINGSTAR2.CO.UK>
Subject: Re: Catcode changes
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Status: R

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 :-)

> 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.

Joseph