Re: markdown - pdf two way sync

[BH <bewihelm-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

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On Tuesday, May 3, 2016 at 2:39:05 PM UTC-4, John MacFarlane wrote:
>
> Pandoc doesn't store any source-mapping information in 
> the AST. 
>

This is, of course, right, but two-way sync (in both directions) is 
possible nonetheless (albeit in a way that's quite fragile). Here's the 
rough idea (both requiring that pdfsync be used when compiling the .pdf 
file):

1. For backward search (from .pdf to .md): have the .pdf viewer send the 
source (.tex) file and line number to a script that (a) reads in the 
relevant line from the .tex file, (b) extracts a reasonable-sized chunk of 
text, (c) searches for that text in the corresponding markdown file, and 
finally (d) sends the line number of that text to the text editor.

2. For forward search (from .md to .pdf) do the opposite: have the text 
editor send the source (.md) file and line number to a script that (a) 
reads in the relevant line from the .md file, (b) extracts a 
reasonable-sized chunk of text, (c) searches for that text in the 
corresponding .tex file, and finally (d) sends the line number of that text 
to the .pdf viewer.

Clearly, a problem lies in step (b) in both cases: how do you locate the 
relevant text to use in searching the corresponding file for? What I've 
done differs between (1) and (2).

In (2), I find it easiest to take the whole line of markdown, strip off any 
initial markdown codes (such as those for enumerated lists), run it through 
pandoc (using exactly the same options I use to generate the .pdf in the 
first place) to convert to LaTeX, and then search for this in the .tex file.

In (1), I find I need to use a different strategy, since .tex -> .md 
conversion in pandoc often fails to produce a match in the .md file. (This 
is partly because of the way I have extended markdown using some filters.) 
So here I try to locate a stretch of text in the .tex file that does not 
contain any LaTeX commands as follows: I try searching for the first 
occurrence of '\' in the relevant line, and if this occurs deep enough into 
the text, I grab text from the beginning of the line to that point. If not, 
I look for a stretch of text after that '\' that occurs between '{' and 
'}'. Usually this is good enough to find a unique match in the markdown 
file.

As I said, this is fragile: it won't work in every case, but for me it 
works about 90-95% of the time, which is good enough for my purposes.

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