expresso

Declarative slide deck DSL and presenter in Elixir.

Expresso makes one HTML document from a deck. The document holds each slide, the styles and a small script. Open the document in a browser, and present from there.

Status

Expresso is at an early stage. It has 27 built-in themes and these elements: text_box, text_area, image, list, table, quotation, spacer, code, columns, math, diagram, embed, video, audio, qr_code, footnote, shape, chart, tree, callout, toc, stat and icon.

Overlays are the steps inside one slide. A slide takes steps, and an element shows at a set of steps. The document also holds a handout view for a printer. docs/overlays.md gives the design.

Install

Expresso needs Erlang/OTP 29, Elixir 1.20 and Node 24. The file .tool-versions gives the exact versions. The Nix shell of the repository has each tool:

nix develop      # or: direnv allow, after you copy .envrc.example to .envrc
mix deps.get

Without Nix, docs/development/toolchain.md tells how to get the same versions.

Quick start

Write a deck in my_deck.exs:

defmodule MyDeck do
  use Expresso

  name "my deck"

  slide do
    heading "Hello"

    list do
      reveal true
      item "Each item is one step"
      item "Press j for the next step"
    end
  end
end

Render it, and open my_deck.html in a browser:

mix expresso my_deck.exs my_deck.html

Two more options help while you write a deck:

mix expresso my_deck.exs --watch   # serve the deck, and reload it after each change
mix expresso my_deck.exs --check   # check the deck, and write a report

mix expresso --help shows each option. The page of the mix task gives the same text. Make your first deck takes you through each step.

Documents

https://rellen.github.io/expresso/ shows the documents and the API. The documents have four types:

• Tutorial: Make your first deck teaches the basics in one session.
• How-to guides in docs/how-to/ give the steps of one task, such as Present a deck, Animate elements in a slide and Show data in a chart.
• Reference pages in docs/reference/ describe each element and each option, with the deck options and the presenter, which gives each key.
• Explanation: docs/architecture.md tells how the code makes a document, and docs/overlays.md gives the design of the steps inside a slide.

Develop

mix check runs each check: the compiler, the formatter, Credo, Dialyzer, Sobelow, the tests, the browser tests, the binary and its tests. CONTRIBUTING.md tells how to send a change. docs/development.md tells how to get the toolchain, run each check and make a binary. CLAUDE.md gives the conventions for a commit message and for prose.

License

Apache License 2.0. See LICENSE.

The built-in theme uses Atkinson Hyperlegible, Copyright 2020 Braille Institute of America, Inc. That font is under the SIL Open Font License, Version 1.1, and assets/fonts/OFL.txt holds the license. Each document that Expresso makes holds the bytes of the font, so the document needs no network.

Expresso holds the Lucide icons, Copyright Lucide Icons and Contributors, under the ISC license. The icons that come from Feather are Copyright Cole Bemis, under the MIT license. priv/icons/LICENSE holds the two licenses. A document holds the SVG of each icon that its deck uses.