[texhax] Advanced Ligature Handling in .pl Files

[Pierre MacKay]

On 09/13/2009 09:20 AM, Stan wrote:
> I would like to use some of TeX's (Metafont's?) smarter ligature 
> capabilities (described under the headings "smarter ligatures" and 
> "boundary ligatures" in the article 
> www.tug.org/TUGboat/Articles/tb10-3/tb25knut.pdf) in fonts for which I 
> already have .tfm files.  I've successfully specified some ligatures 
> ("ff", "fi", etc.) using what I learned from this page:
>
> http://www.slac.stanford.edu/comp/unix/package/tex/web2c/web2c_10.html
>
> but this page does not talk about the more advanced ligature 
> handling.  (I used tftopl on the .tfm file for the font in question, 
> added some entries to the ligtable, and then converted the .pl file 
> back to a .tfm using pltotf.  This process worked for "standard" 
> ligatures.)  I tried variations on the syntax specified in the Tugboat 
> article, as well as on pages 316 and 317 in appendix F of The Metafont 
> Book, but that doesn't seem to be for .pl files.
>
> Is there a way to specify the more advanced ligature handling in .pl 
> files?  Also, are there any other resources that discuss the syntax to 
> use in .pl files?
The details came out in a sort of news-letter form in the same year that 
DEK conceded the addition of some details to TeX.  We are back, I think 
in the late 80s for this, and perhaps someone with a less leaky memory 
than I have can recall where to find a copy of this newsletter.  It is 
associated with the designation TeX3.xxxxxx and the beginning of version 
control based on pi.

At the moment, the best I can do is give you an example where the 
advanced techniques are very much in use.  Most of what I did depends on 
the use of the slash, which causes the letter you are
using in a ligature to be retained for further evaluation.  That is how 
w(=| gets turned into an omega with three accents.

The ibylig4.mf file has all the ligatures for ibycus coding.  The use of 
the vertical bar is something that you may be able to decipher, but I 
grant you it is not easy, even for me after all these years.

I know that this is deplorably opaque, and helps only a little.  What 
you really need is the DEK description, and I hope someone can find you 
a copy.

Pierre MacKay
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