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, Poetry and Verbatim blocks, better image handling, extensible block and inline elements, SVG figures, apply a CSS class to an inline element
• 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, follow the code in ./example/src, e.g,

view model =
    Html.div []
        [ Markdown.Render.toHtml ExtendedMath sourceText
            |> Html.map MarkdownMsg
        ]

This example shows how to include mathematical formulas and SVG figures. To run the example, do this:

$ cd example
$ sh make.sh

Then open public/index.html with your browser.

Demos

See the ./Demos folder for examples. Best to look at ./Demos/simplest first.
The other examples include extra bells, whistles and optimizations that are useful for interactive editing environments and documents with a lot of mathematics.

Links to live demos:

• simplest
• simple — includes export to MiniLaTeX.
• markdown.minilatex.app

This package is still evolving. 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

Installing a Demo

For example:

$ cd to ./Editors/fancy

$ vr make

NOTES

• vr is the command for Umberto Pepato's script runner, Velociraptor. It is elegant and simple, with the scripts stored in scripts.yaml To use it, you need to have installed Deno, advertised as a modern and secure runtime for JavaScript and TypeScript that uses V8 and is built in Rust.

• If you don't use Velociraptor, just peek inside scripts.yaml for whatever shell commands you need. Usually just the make command.

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 apps are found in ./public/assets/style.css when you are in the folder for one of the Editor examples. You can easily reconfigure the CSS to satsify your own esthetics.

Markdown extensions

Here are the main additions:

• Poetry blocks are are like quotation blocks, except that they begin with ">>" instead of ">". White space and 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.

• Tables

• Extension blocks. These begin with the token @@, e.g, @@svg for SVG figures as explained below. The general form is @@cmd arg1 arg2 ... on the first line followed by the body of the element: zero or more non-blank lines followed by a blank line. The argument list may be empty. Unimplemented blocks are rendered verbatim. If you want to make a comment in the text but not have it show up in the rendered version, use the @@invisible block, like this:

  @@invisible
  This is not to be seen!

• Inline extensions. These have the form @cmd[arg] For example, the text @red[very hot stuff] renders very hot stuff in red. The cmd is a CSS class name, and that class is applied to the text arg. The class name can be anything, but to have an effect, it must be defined in ./public/assets/style.css. We have defined the following CSS classes: red, green, blue, pale, highlight, and censored. The first four color the text. The last two change the background color: yellow, yellow, and black, respectively. We may define more interesting inline extensions later that do not rely on CSS, or entirely on CSS.
  For these, the cmd will be a kind of reserved word. We think of it as a function that is applied toarg. The CSS definitions should reside in public/assets/style.css. See that code in Demos/simple.

SVG

You can add SVG images like this:

@@svg
<svg width="100" height="100">
<circle cx="50" cy="50" r="40" stroke="blue" stroke-width="3" fill="cyan" />
</svg>

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:

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

where Version is an integer and Document is a type alias for String.
This is also useful if you wish to transform the abstract syntax tree before rendering it. The Version parameter may be set to zero if you do not have to worry about updated thd ids of rendered elements in an interactive editing environment.

Editor

The fancy demo app now uses pure Elm text editor. It is very much a work in progress.

Bugs and whatnot

Please write me at jxxcarlson@gmail.com 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

Recent Changes

• Added nolang support for the syntax highlighter. Thus in code blocks set off by triple backticks where the language is not supported by the syntax highlighter, use nolang in place of elm, python, etc. Currently supported languages are css, elm, javascript, json, python, sql, and xml.

• Added the function Markdown.LaTeX.export to export Markdown text to MiniLaTeX.

• Added the function Markdown.Parse.toTextTree : Tree MDBlock -> Tree String

• Added the @@-block element to the parser. Allows further extension to the syntax (see section SVG above)

• Made substantial changes to simplify the API.

• Changed the return type of the rendering functions: the return type Html msg is replaced by Html MarkdonMsg. This change makes the rendered text "active," e.g., can respond to clicks. See next item.

• Added sourceMap : Tree MDBlockWithId -> BiDict String String in the Markdown.Parse module as a hook for host programs to implement bidrectional sync of source and rendered text.

Thanks

Thanks to Folkert de Vries and Luke Westby. A shout-out to Folkert for an optimiztaion of the pure text rendering (10 x speedup). A thankyou to Anton-4 for significant code cleanup and adding nolang support for the syntax highlighter.