Re: [PATCH] Understand EQ/EN blocks.

[Ingo Schwarze <schwarze@usta.de>]

Hi Kristaps,

> Enclosed is a patch that sets us down the road of understanding
> EQ/EN blocks.

From reading, merging and running it, this makes sense to me.

[...]
> The equations themselves are thrown away.  This is only because I
> wanted to float a patch early with the libroff framework.  It's
> trivial to put an addspan() style routine to both libmdoc and libman
> that at least print out the data.  I'll do that with an Ok or two.

That is indeed the logical next step.

> Thoughts?

I guess i would merge it for release if we get at least a bit
added value compared to just ignoring the .EQ lines with an ERROR,
as we currently do.  After looking at

  http://heirloom.sourceforge.net/doctools/eqn.1b.html

i think the easiest and most useful bits that could make rendering
better are:

 * remove "left" and "right"
 * pass through strings enclosed in double quotes "..."
   untouched, removing the quotes
 * convert "over" to "/"
 * convert "x sub i" to "x_i" and "x sup n" to "x^n"
 * replace ~ and ^ by a space, and collapse multiple spaces,
   tabs, and/or newlines to become a single space
 * remove spaces after ({[ and before )}]

A bit less important:

 * remove "size [+|-]n", roman, italic, bold, "font n",
 * remove "mark" and "lineup"

Much less important:

 * implement roman, italic, bold
 * implement under

Everything else should probably just be passed through, at least
for now:

 * Let braces { } be braces, converting them to parentheses ( )
   would just make the eqn text harder to grok, having lots of
   adjacent, similar tokens in some formulae.
 * just keep keywords like: sqrt, from, to, pile, matrix, ccol,
   dot, hat, tilde, bar, vec, sum, int, inf
 * leave "define" untouched
 * don't worry about GNU extensions for now

> By the way, we'll be able to fully support "delim", as libroff
> allows us to chop up its input lines and send them to the other
> backends, so
> 
>  foo $a + b$ bar
> 
> assuming `$$' are the EQN delimiters, would be passed back as
> 
>  foo
>  EQN:a + b
>  bar

That does seem worthwhile, too, maybe even more useful than the
two items marked "less important" above.

Thanks for getting this started,
  Ingo
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