Re: implementing K-P in a macro (was Re: Mission statement and Knuth-Plass reconsidered)

[Douglas McIlroy]

K-P would not be a mere add-on to groff. K-P knows in advance the
shape of the space into which a paragraph must fit, but groff doesn't.
This means a whole lot of groff state must be carried along with the
K-P dynamic program. The latter merely needs to keep a set of
candidate line-break points.

For example, an image around which the text must flow can be pinned to
a word (actually to whatever line that word finally appears in) by
non-breaking 'll and 'in requests. Then the end of the image a fixed
distance ahead can be specified by .wh. All of these settings are made
dynamically as type is set and thus vary with breakpoint choice

I have suggested a conceptually simple, but probably exorbitantly
expensive, implementation: run multiple copies of groff in parallel,
each picking different breakpoints. Kill off all but the best instance
at each paragraph end. The degree of parallelism could be limited to
the maximum number of words on a line, at the cost of IPC among the
instances of groff. Now it gets ugly!

Doug