Delta

Beta. Delta is usable and published on npm as delta-lang (the CLI command is delta). The language and output are still evolving — expect changes before 1.0.

Delta is a LaTeX-inspired XML markup language for scientists — mathematicians in particular — and students to write interactive books, articles and presentations. A .dlt file compiles into a single standalone HTML file that works offline, straight from file://: math, numbering and cross-references are all resolved at compile time, so nothing is fetched at runtime.

Install

npm i -g delta-lang
delta build doc.dlt -o doc.html      # then open doc.html in any browser
delta build doc.dlt -o doc.html --watch   # rebuild on every change

The package name is delta-lang (the bare delta name was taken on npm); the installed command is delta.

--watch (or -w) keeps delta running and recompiles whenever the document or anything it pulls in changes — <include> files, the theme CSS, <import> packs, the .ref bibliography, figure images, or project.toml. Press Ctrl-C to stop.

<document lang="en" type="paper">
  <title>Hello, Delta</title>
  <section id="sec:intro">
    <title>Introduction</title>
    Inline math like $e^{i\pi} + 1 = 0$ just works — even $a < b$.
    <theorem id="thm:pyth">
      <title>Pythagorean Theorem</title>
      <equation id="eq:pyth">a^2 + b^2 = c^2</equation>
    </theorem>
  </section>
</document>

How it works

Every tag becomes a <delta-tag> custom element in the output. The compiler resolves data — LaTeX-style numbering (Theorem 1.2), reference targets, KaTeX HTML — and ships it as attributes and pre-rendered content; the inlined runtime renders the chrome (headers, collapsing, pop-overs). KaTeX itself never ships to the browser, only its CSS with fonts embedded as data: URIs.

Extending Delta is meant to be easy: a new numbered environment is one row in src/compiler/environments.ts, and a new interactive tag is one custom element under src/runtime/elements/.

From source

npm install
npm run example        # compiles examples/hello.dlt → out.html, open it in a browser
npm test               # vitest
npm run build          # dist/cli.js
node dist/cli.js build mydoc.dlt -o mydoc.html

Status

Beta: the core pipeline (preprocess → parse → number → math → emit) works end-to-end. See ROADMAP.md for what's done and what's next.

Documentation

• docs/ARCHITECTURE.md — how the compiler works: the pipeline traced end-to-end, the three core concepts (AST, context, environments table), and the compile-time/runtime split. Start here to understand the repo.
• docs/CONTRIBUTING.md — how to add features: the dev workflow and the three shapes every feature takes, each with a worked example.
• docs/COMPILER_BOOK.md — the deep field guide: a chapter-by-chapter walk through every compiler pass and the context it threads.
• docs/BUILDING.md — the build: the generated assets, the CLI bundle, and every npm script.
• ROADMAP.md — planned features in dependency order.

Authoring notes (strict XML)

• No valueless attributes — write collapsible="true", not bare collapsible.
• <, > and & are fine inside math and code; in prose, use <, >, &.
• $…$ inline, $$…$$ display, \$ for a literal dollar.
• <equation> is display + numbered; <m> is inline; <equations> is an aligned block (use & and \\ directly — no escaping inside it).