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David Kastrup <[log in to unmask]>
Reply To:
Mailing list for the LaTeX3 project <[log in to unmask]>
Thu, 10 Nov 2005 11:42:58 +0100
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Heiko Oberdiek <[log in to unmask]> writes:

> On Thu, Nov 10, 2005 at 09:03:16AM +0100, Uwe Lück wrote:
>> At 07:52 10.11.05, Will Robertson wrote:
>> >Finally, somehow the topic of extensions to pdf-e-TeX came up, and
>> >there were some naive comments from me and some interesting comments
>> >from Morten. I proposed the idea of something like \previouschar,
>> >which we interpreted in two separate ways:
>> >
>> > - it "would return the slot number of the most recently seen char
>> >or ligature node independently of whether we just saw a glue node or
>> >another char/lig node; any other node type could reset it to
>> >-1" [morten]
>> >
>> > - it would actually be more like LaTeX's \@ifnextchar, and look at
>> >the input token list [me]
>> >
>> >Implicit in my thinking was that you could also eat up previous chars
>> >in the same was as \unskip with a sort of fine-grained \lastbox; to
>> >which idea Morten replied:
>> >
>> >  This is exactly what some languages need.
>> >
>> >  Since there are so many different node types the only safe
>> >  (IMO) way is to backtrack one node at a time so ideally we
>> >  would want the pair \lastchar and \unchar. And then we might
>> >  as well get one for each different node type. I guess someone
>> >  has to come up with a good idea about what to do with \discretionary
>> >  because I'm not at all sure what the semantics should be.
>> by accident, this occurred to me as well, if only for a
>> rather fun application. \lastchar 
> And what kind of object is the return value of \lastchar?
> A number is quite useless, because this misses the font property.

It does not seem to be too useful if one can't deal with the last
"character" being a ligature.

David Kastrup, Kriemhildstr. 15, 44793 Bochum