vscode-elo

Elo language support for Visual Studio Code.

Syntax highlighting via a TextMate grammar, plus comment toggling, bracket matching and indentation for .elo files.

This is the third grammar in contrib/, because the three ecosystems need three different formats and none of them can consume the others:

Install

From source, for development

Symlink the directory into your extensions folder and restart VS Code:

ln -s "$PWD" ~/.vscode/extensions/enspirit.vscode-elo-0.1.0

As a .vsix

npm run package                            # npx @vscode/vsce package
code --install-extension vscode-elo-0.1.0.vsix

Publishing

Marketplace. publisher is set to enspirit. The publisher ID is an Azure DevOps identity, unrelated to npm or GitHub: sign in at https://marketplace.visualstudio.com/manage to check or create it, then npx @vscode/vsce login enspirit and npm run package && npx @vscode/vsce publish. At the time of writing neither enspirit nor elo-lang is taken.

npm. vsce refuses to combine a .vscodeignore with a files property, so this package uses files — the .vsix and the npm tarball then ship exactly the same 11 files. npm publish works as is and puts the TextMate grammar within reach of anything else that consumes one (Shiki, for instance, which could render the website's code blocks).

One wrinkle worth knowing: a VS Code extension name cannot be scoped, so this package is vscode-elo on npm, not @enspirit/vscode-elo like its two siblings. Keeping the @enspirit scope would mean splitting the grammar into a separate package that the extension then embeds.

What gets highlighted

• Keywords — let, in, if, then, else, guard, check, fn, and, or, not
• Types — the built-in selectors (Int, Float, String, Date, …) get support.type.builtin, and any capitalised identifier gets entity.name.type, because Elo reserves capitalised identifiers for type names (see codemirror-lang-elo/src/tokens.ts). So Person, PosInt and Parametres colour as types without being listed anywhere.
• Finitio constraints — in Int(i | positive: i > 0), i is a parameter and positive a constraint label
• Lambda parameters — both fn(x, y ~> …) and the x ~> … sugar
• Temporal literals — D2024-01-15, D2024-01-15T10:30:00Z, P1Y2M3D, PT1H30M, and the keywords NOW, TODAY, SOW, EOT, …
• Standard library — map, filter, round, assert, fetch, … get support.function; your own calls get entity.name.function
• _ — the implicit input, scoped variable.language.input
• Operators — |>, ~>, .., ..., comparisons, arithmetic, | for union/alternative, ? for optional attributes
• Strings with \\, \n, \t, \r, \' escapes; unknown escapes are flagged invalid.illegal
• Let bindings — the name being defined gets variable.other.definition

Plain variable references are deliberately left unscoped, so they take the theme's default foreground — same convention as the built-in grammars.

Icons

Both the Marketplace icon and the .elo file icon are derived from web/public/logo.svg — the three bars standing for the three compilation targets, a stylised E, and the |> pipe. Colours come from the website's design tokens (web/public/styles/tokens.css):

The SVGs are the source; the PNGs are what VS Code actually loads. Regenerate them with npm run icons (needs ImageMagick) after editing an SVG.

Tests

The grammar is tokenised with the real VS Code engine (vscode-textmate + Oniguruma) and the scopes are asserted, so a regression shows up as a failing test rather than as a colour someone notices later.

npm install
npm test                           # assert scopes on fixtures/sample.elo
node test/tokenize.test.mjs --dump # print every token and its scopes

fixtures/sample.elo is valid Elo — it parses with @enspirit/elo — and exercises every construct the grammar has to colour. Besides the explicit scope assertions, the suite fails if any token containing an operator, a digit, a capital or punctuation ends up with no scope at all: that is how a hole in the grammar gets caught.