jxxcarlson/elm-markdown

The aim of this Markdown library is to provide a pure Elm implementation of Markdown which offers a small set of optional extensions:

• Standard: the usual thing
• Extended: strike-though text, tables, and Poetry and Verbatim blocks, better image handling
• ExtendedMath: like Extended, but math formulas written in TeX/LaTeX, eg.,

This **is** a test: $a^2 + b^2 = c^2$.

are properly rendered.

How to use it

For simple applications, use the Madrkown.Elm and Markdown.Option modules, as in these examples:

Markdown.Elm.toHtml Extended "This **is** a test."

Markdown.Elm.toHtml ExtendedMath "Use $a^2 + b^2 = c^2$."

where in Markdown.Option one has

type Option
    = Standard
    | Extended
    | ExtendedMath

For the ExtendedMath option, take a look at ./app-demo/index.html in the source code to see what to do. You will need some Javascript, incuding MathJax 3.

Demo

There are two versions of the demo, a basic one in ./app-demo/, another in app-demo-fancy which has more features and some optimizations that are useful for documents with a lot of mathematics.

See markdown.minilatex.app for a demo of the latest implementation the fancy demo.

NOTE: This package is still evolving relatively rapidly. I regret publishing so many updates, but I am using it in several apps, and this is the only way I know how to encapsulate the complexity, work with the CI build systems, and keep my sanity

Style

The style used by the library is entirely determined by the definitions of the CSS classes that you refer to in your index.html. The ones used for the demo app are found in ./app-demo/assets/style.css and ./app-demo-fancy/assets/style.css You can easily reconfigure the CSS to satsify your own esthetics.

Markdown extensions

I am trying to be conservative about extensions to Markdown. However, there are two that I thought important enough to add: tables, poetry blocks and verbatim text. Poetry blocks are are like quotation blocks, except that they begin with ">>" instead of ">". Line endings are respected in poetry blocks. Verbatim blocks are like code blocks, except that they are set off by four backticks instead of three. No syntax coloring is applied to verbatim blocks.

Images

The usual ![My favorite image](imageUrl) does the usual thing, with the image scaled to 100% of the width. You can also say ![My favorite image::left](imageUrl) or ![My favorite image::right](imageUrl) to float the image left or right at 40% width. The widths are defined in style.css.

Advanced Usage: AST

If you wish to write your own renderer, or do other fancy things, you will want to produce and manpulate the AST:

Parse.toMDBlockTree : Option -> Document -> Tree MDBlock

where Document is a type alias for String. This is also useful if you wish to transform the abstact syntax tree before rendering it.

Editor

This section is relevant only to those wanting to implement a "fancy" editor that interacts with the rendered text in some way, e.g., sync of source and rendered text, as described below.

Following Luke Westby's talk at Elm Europe 2018, I've implemented an editor using custom elements and Codemirror.js. In addition, there is a start on a system for synchronizing the source text in the editor (Left) and the rendered text (Right). If one clicks somewhere in the gutter of the editor, the right-hand window scrolls to display the corresponding rendered text. There are quite a few moving parts to this system. Codemirror detects the click, finds the line number, and returns the corresponding text as string, forwarding this info to Elm. The function ElmWithId.searchAST finds the id of the corresponding element the AST (parse tree), which is ultimately used by Browser.Dom.setViewportOf to set the viewport of the rendered text window.

The system is not yet foolproof, the main weak point being that searchAST does not always find its target This is "Left-to-Right" sync. We also want to implement Right-to-Left sync.

All this editor stuff requires the following lines in index.html

  <!-- Text Editor -->
  <link rel='stylesheet' href='lib/codemirror.css'>
  <script type='text/javascript' src='lib/codemirror.js'></script>
  <script type='text/javascript' src='assets/code-editor.js'></script>

Bugs and whatnot

Please write me at [email protected] or post an issue on the Github repository regarding bugs or anything else. I will steer this library towards the Commonmark spec to the greatest extent possible by the method of successive approximations

Thanks

Thanks to Bill St. Clair, Folkert deVries, and Luke Westby. A shout-out to Folkert for an optimiztion of the pure text rendering (10 x speedup).