[Dev-luatex] A design philosophy question...

David Kastrup dak at gnu.org
Tue Apr 3 09:21:28 CEST 2007

Hans Hagen <pragma at wxs.nl> writes:

> David Kastrup wrote:
>> Anyway, is something like that an area that LuaTeX would actually ever
>> consider touching?  After all, it would break document compatibility.
>> Which might be, I believe, less of a holy grail for ConTeXt than for
>> LaTeX.
> in extended mode, when using dimexpr one also gets more precission
> so a switch to etex mode may break backward compatibility anyway

Uh, how can there be backward compatibility broken when dimexpr did
not exist previously?  Do you mean compatibility to eTeX?  Nobody
claimed that dimexpr arithmetic is the same as TeX arithmetic (in
fact, it is a **** nuisance that its integer division rounds instead
of truncating).

> concerning context ... truncating vs rounding is less an issue than
> precission (roundtrip calculations resulting in 1+ sp off
> comparisons) but that is/will be covered with special test stuff

TeX's way of always truncating dimensioned expressions is certainly
bad for roundtripping.  That "1in" is not resolved to the same value
as "72.27pt" is what I'd call a roundtrip problem.

> concerning latex and old docs ... there will always be pdftex vs <
> 2, so with luatex we have no intention to be 100% downward
> compatible at all (some internals may also be adapted / extended /
> opened up, some good old tex code may disappear (lig rebuilding
> already has), etc

Interesting.  What do you do instead of ligature rebuilding?

David Kastrup

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