Re: Mission statement and Knuth-Plass reconsid

[Douglas McIlroy]

I hate to keep raining on the persistent dream of K-P in groff, but it
fits poorly with troff's basic typesetting model.  How will it deal
with line-length changes that pop up in the middle of a paragraph, due
to requests that can come inline or from a macro, perhaps triggered by
a trap? K-P faces no such problem; it knows in advance the shape of
the region to be filled with text.

The only obviously sure-fire way I have thought of to cope with all
the daunting scenarios is to fork a groff copy for each trial
breakpoint, run them in parallel, and pick the best at paragraph's
end--elegant, but probably slow by a significant factor. A perhaps
pracitcal adaptation would be to fall back on parallel evaluation only
upon encountering changes of state other than certain routine per-word
updates of horizontal and vertical position.

I also cite fmt(1) as a cautionary tale. It does notably worse than
nroff  on unjustfied text. Each paragraph ends up  with roughly
equalized lines, but evey paragraph gets its own apparent width--a
highly visible phenonomenon. K-P is more sophisticated, but I suspect
it exhibits the same symptom.

Doug