[Dev-luatex] Trouble with hyphenation.

[Paul Isambert]

Hans Hagen <pragma at wxs.nl> a écrit:
> 
> On 18-2-2012 12:08, Paul Isambert wrote:
> > Hello all,
> >
> > I've found some strange behavior with hyphenation; but since hyphenation
> > has been discussed frequently, and might involve some settings in conf
> > files somewhere I'm not aware of, I wouldn't like to submit an unnecessary
> > tracker item in case the problem is well known. The code is:
> >
> >        \hsize=0pt \overfullrule=0pt
> >        \hyphenation{W-h-a-t-e-v-e-r}
> >
> >        \uchyph=1
> >        Acceptation Behavior Dying Expression Whatever
> >
> >        \uchyph=0
> >        Acceptation Behavior Dying Expression Whatever
> >        \bye
> >
> > And comparing the plain TeX compilation in PDFTeX and LuaTeX (all
> > from TL2011, except LuaTeX, which is rev 4358), I notice that:
> >
> > - LuaTeX doesn't obey \uchyph=0; it does hyphenate the words, although
> >    not as completely as when \uchyph=1.
> 
> I must admit that I never used \uchyph (and even wonder if we really 
> need it as it's a kind of tweaking that seldom is done at the document 
> level). I would have expected this primitive to do nothing at all in 
> luatex.

Actually, it is explicitly mentioned in section 6.1 of the manual,
stating that it is effective immediately, not at the end of the paragraph,
since its value is stored in nodes themselves. I don't find it terribly
useful either, but who knows what trickery has been based on it.

> > - "Acceptation" is hyphenated in LuaTeX even though it's the first word,
> >    and a hyphenable word should be preceded by a glue (see TeXbook p.256);
> >    it is not hyphenated in PDFTeX.
> 
> luatex hyphenates the whole list in one go and does not do this delayed 
> and partial as in traditional tex ... this is on purpose as it provides 
> callback code with the whole lot (in luatex the hyphenation / ligature 
> building and justification steps are separated) ... also, there is no 
> reason not to hyphenate the first word if you have real narrow columns.

I agree, it's just that TeX3 does otherwise.

> > - As shown by the hyphenation of "Whatever", LuaTeX disregards
> >    \lefthyphenmin and \righthypenmin.
> 
> Explicit \hyphenation always wins and is not influenced by the *min 
> values (after all, it is mostly meant as a an escape for providing 
> exceptions and not for extending the patterns so obeying the *min 
> parameters would defeat that purpose).

The parameters are obeyed in all other engines, exception or not; I
suppose the reason is that they may very well change in the course of
the document.

But actually I've just found things are a little bit more complicated:
LuaTeX doesn't hyphenate a word if it is shorter than \lefthyphenmin +
\righthyphenmin (which makes sense); but if the word is hyphenated, and
it is an exception, then it gets hyphens everywhere, whatever the values
of the parameters:


      \hsize=0pt \overfullrule=0pt
      \hyphenation{a-b-c d-e-f-g h-i-j-k-l m-n-o-p-q-r}

      \lefthyphenmin=2 \righthyphenmin=3
                 abc  defg  hijkl      mnopqr       castle   keepers
      % PDFTeX = abc  defg  hi-jkl     mn-o-pqr     cas-tle  keep-ers
      % LuaTeX = abc  defg  h-i-j-k-l  m-n-o-p-q-r  cas-tle  keep-ers

      \lefthyphenmin=4 \righthyphenmin=1
                 abc  defg  hijkl      mnopqr       castle  keepers
      % PDFTeX = abc  defg  hijk-l     mnop-q-r     castle  keep-er-s
      % LuaTeX = abc  defg  h-i-j-k-l  m-n-o-p-q-r  castle  keep-er-s

      \bye


This half-obeying the parameters does seem quite strange to me.

Best,
Paul