Re: [groff] mark/lineup in eqn

[Doug McIlroy]

Ingo,

Interestingly your comment is the first I have
received that is not of the form "you can jigger
this or that to get the desired effect". And indeed
I had over the  years  used every one of those tricks plus
one more: assemble the parts with tbl rather than
with an eqn matrix. I thought all of them were more
like hand-setting type than recording math.

However, I suspect the real reason that mark/lineup doesn't work
within a pile is that it wasn't considered. I see no
fundamental difference  between aligning on a mark and
aligning on any other point such as the center or
the right end. The only added complexity I see is that
one must keep track of two lengths rather that just
one within each line.

Doug

Date: Wed, 2 May 2018 17:53:17 +0200
From: Ingo Schwarze <address@hidden>
To: Doug McIlroy <address@hidden>
Cc: address@hidden
Subject: Re: [groff] mark/lineup in eqn
You may think that pile/pile/pile and matrix are able to do it and
produce the correct indentation inside a single .EQ block, so
mark/lineup should also be able to as well.  But i fear that misses
the crucial point.  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.