Re: markdown writer line wrapping

[John MacFarlane <fiddlosopher-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

+++ John MacFarlane [Nov 23 10 19:25 ]:
> +++ Nathan Gass [Nov 24 10 02:51 ]:
> > Some questions about the line wrapping implementation for the
> > markdown writer.
> > 
> > Is it correct that line wrapping only happens at the top level, so
> > something like *very long emphasized text ... end of it* currently
> > does not get wrapped?
> 
> Right.
> 
> > And how would I go about to implement arbitrary deep line wrapping,
> > so that something like *very long empahsized text [with a very long
> > citation inside for @key p. 10]* gets wrapped correctly?
> > 
> > How does line-wrapping work in pandoc?
> 
> See wrapped in Text.Pandoc.Shared.  (Also wrappedMarkdown in the
> Markdown writer, which handles complications due to line breaks.)
> 
> You're right, it splits an [Inline] by Space at the top level, then applies a
> function [Inline] -> m Doc to the sublists that result, then applies
> fsep (from the PrettyPrint library) to combine the resulting [Doc]
> into a single Doc with line wrapping.
> 
> Unfortunately, I can't see an easy fix (one that doesn't require major
> architectural changes).

I've been working on a small prettyprinting library to use instead
of the one from 'pretty'.  It's designed to be a better fit from pandoc,
and it solves this line wrapping issue.

Unfortunately, it's currently slower than the standard prettyprinting library.
If you want to look at it, it's in the 'pretty' branch of jgm/pandoc on
github.

I haven't worked much yet on optimizing it, and so far I've just worked
it into the markdown writer -- and only incompletely.
Benchmarks show that it's significantly slower than the old version.
33 ms vs 18 ms.

Nonetheless I'm thinking about using it to replace Text.PrettyPrint.HughesPJ
throughout, if it can be optimized a bit...  Right now I'm using DLists;
I might try using Blaze.Builder.

John