Re: Vertical lines for delimiting chunks ot text

[Jeff Kingston]

On one page, what Paul asks for is quite easy to organize:

    def @Theorem
         named statement {}
         named proof {}
    {
        @B Theorem %%
        @LP
        @SemiBox statement
        @LP
        @B Proof:
        @LP
        @SemiBox proof
    }

where @SemiBox is

    def @SemiBox right x
    {
        { 0 0 0 ysize stroke } @Graphic x
    }

or rather { ||1f x } to allow a little space between the line and text,
and %% stands for numbering magic that would have to be copied from the
existing @Theorem definition.

However, this is not going to break across pages except at the obvious
gap points.  To do that is very much harder, requiring the @Enclose
symbol as used to get boxes around floating figures.  Lout really needs
a concept of "galley hyphenation", i.e. it should be possible to tell
Lout that an object can be broken halfway through, and that the resulting
pieces should have a certain appearance.  But, unfortunately, this
feature, although quite feasible, has never been implemented.

An alternative approach that might be even better would be to (excuse
the technicalities) inform Lout that certain receptive symbols may
be promoted before being finalized.  Then we could promote a @TheoremPlace
receptive symbol onto the current page, and proceed to promote the
lines of the theorem one by one into it.  I think this would require
only a small extension to the Lout kernel language, one that would not
be very hard to implement.

Jeff