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