To begin implementing Nodo we need to make a start with Rust. This means creating a new workspace and some subdirs for crates. I’ll use a workspace to ease the management of multiple crates (I’m planning one for the core and another for each frontend).

All formats we want to implement will need to implement a trait. So we can separate the functionality into two traits:

pub trait Parse {
    type ParseError;

    fn parse(s: &str) -> Result<Nodo, Self::ParseError>;

pub trait Render {
    type RenderError;

    fn render<W: std::io::Write>(n: &Nodo, w: &mut W) -> Result<(), Self::RenderError>;

These together tell us that each formatter can provide a parse function and a render function. So if a particular formatter only implements the Parse trait then it may not be able to be rendered yet. This is fine in it’s other form too, Render without Parse, as that can be for example the JSON API, which may need to read from a Markdown file and just return the JSON formatting.

For an implementation of these traits I’ve started with just the markdown module. This is going to be the main format for now at least. We can use a simple unit struct to give us something to implement our traits on:

pub struct Markdown;

And then implement the traits like so, for full code reference see the Git Repo link:

impl Parse for Markdown {
    type ParseError = ParseError;

    fn parse(s: &str) -> Result<Nodo, Self::ParseError> {
        let mut opts = Options::empty();
        let blocks = parse_blocks(&mut (Parser::new_ext(s, opts)).peekable())?;
        Ok(Nodo { blocks })

impl Render for Markdown {
    type RenderError = RenderError;

    fn render<W: std::io::Write>(n: &Nodo, w: &mut W) -> Result<(), Self::RenderError> {
        render_blocks(&n.blocks, "", w)?;

With some enum error types, defined using the thiserror crate, very simple. These can then be called (when the trait is in scope) with Markdown::parse(...) and Markdown::render(...), respectively. I used the std::io::Write trait for the render function so that we don’t have to explicitly write it all to a String, and can instead go straight to a file. This could have been mimicked with std::io::Read, or a relative of, and the parse function, however the pulldown_cmark crate doesn’t provide such a utility so it wouldn’t have made as much sense. I may change this to allow other parsers to read straight from a file or other compatible source though.

So far there have been some unexplained things such as the implementations of Nodo, ParseError and RenderError. These are not so important as I don’t want to get into all of the parsing logic too much but more outlay my high level thoughts, yes I’ve written the code, no it is likely not in a finished state, whatever that means.

One other thing I’d like to briefly mention was my experience implementing the functionality here. Rust gives us powerful mechanisms to manipulate our structures as well as ensuring we aren’t being too silly with them, mostly here was a lot of match statements. This just gives me confidence in the code as well as a nice way of seeing how many cases you have left to implement, a little welcome motivation.

Oh, and getting to use peekable was nice. I needed it for checking if a list item has a TaskListMarker and parsing tight paragraphs which don’t come with much warning and also don’t have a nice tagged ending, stumped me for a while.

Next, I need to think whether I want to have a CLI or work on the internals some more…