Re: [groff] mark/lineup in eqn

[Tadziu Hoffmann]

> The reason why pile/pile/pile and matrix work seems to be
> precisely because the tokens are presented out of order in
> the source code, column by column, and that is precisely what
> you do not want to carry over to your proposed mark/lineup
> semantics.

I don't think the out-of-order aspect is essential; the
creators of eqn probably just considered column-wise input
more "natural" for the cases they envisioned.  LaTeX employs
row-wise input for both matrices and equation arrays (the
equivalent to eqn's mark/lineup), thus keeping the natural
order in inputting successive equations.  (Without looking
at the code, I assume you have to store all the elements
internally in some structure representing the matrix first,
so eqn could probably also be modified for row-wise input.)

The point is simply that you cannot begin layouting the
equation(s) until all required information has been input,
and this somewhat clashes with troff/eqn's division of labor,
eqn deciding on the relative placement of the parts of the
equation, and EQ/EN dealing with how to place the entire
chunk on the page.

And then there are further issues to consider, such as
numbering of equations, where to allow page breaks, etc.