Syntax Highlighting for Your Blog

The Elo website has had syntax highlighting since day one, thanks to a custom tokenizer built into the site. But if you write about Elo on your own blog — say, with markdown-it or Hugo — your code blocks looked plain.

Not anymore. We just published highlightjs-elo, a highlight.js language grammar for Elo. It lives in the contrib/highlightjs-elo directory, alongside the existing CodeMirror grammar that powers the playground.

What it highlights

Keywords, literals, operators, stdlib functions, type selectors, date and duration literals, data paths, comments — the full language surface. Here are a few examples (click any block to try it live):

A simple conditional:

if 2 + 3 > 4 then 'yes' else 'no'

Let bindings with guards:

let x = 42
guard x > 0
in x * 2

Lambdas, pipes, and stdlib:

[3, 1, 4, 1, 5] |> sort |> unique |> map(fn(x ~> x * 10))

Dates, durations, and temporal keywords:

let deadline = D2026-12-31T23:59:59Z in
let remaining = deadline - NOW in
remaining |> inDays

Type selectors and data schemas:

let PosInt = Int(i | i > 0) in
let Person = { name: String, age: PosInt } in
{ name: 'Alice', age: '30' } |> Person

Data path navigation with fallback:

.user.address.city | 'Unknown'

Setup with markdown-it

Install the package from the repo:

npm install @enspirit/highlightjs-elo

Then register the language and wire it into markdown-it:

const hljs = require('highlight.js/lib/core');
const elo = require('@enspirit/highlightjs-elo');

hljs.registerLanguage('elo', elo);

const md = require('markdown-it')({
  highlight(str, lang) {
    if (lang === 'elo' && hljs.getLanguage('elo')) {
      return hljs.highlight(str, { language: 'elo' }).value;
    }
    return '';
  }
});

Then use fenced code blocks with elo as the language identifier in your markdown files. That’s it.

ES module support

The package ships both CommonJS and ES module versions, so it works with bundlers, plain Node, or browser <script> tags. See the README for browser usage.

Try it

If you write about Elo — a tutorial, a comparison, a deep dive into portable expressions — your code blocks now get proper highlighting out of the box.

Try Elo, read the Reference, or grab the grammar from GitHub.