Loci Syntax for VS Code

Syntax highlighting for the Loci DSL used to describe rules, data dependencies, and computation steps in Loci-based applications.

What this extension highlights

• Loci directives and declarations like $include, $type, type names, storage kinds (store, param, const_store, etc.), and $rule forms (pointwise, singleton, apply, unit, default, optional).
• Rule modifiers and helpers: constraint(...), conditional(...), option(...), inplace(...), prelude/postlude, Loci reduction tags ([Loci::Summation]), constants like EMPTY/UNIVERSE.
• $-prefixed variables (including $variable{n=0}) and Loci namespace calls (Loci::load_module, Loci::makeQuery, etc.).
• Comments (//, /* */), string and numeric literals, and the <-ci->, <-, -> arrows used in rule heads.
• Mixed Loci/C++: unmatched content falls back to the built-in C++ grammar, especially inside { ... } blocks.

Quick use

• Install the extension, open a .loci file, and confirm the status bar shows Loci DSL. Colors come from your theme; this extension provides scopes.
• If VS Code doesn’t auto-detect, switch the language mode to Loci DSL manually.

Customize Loci colors (manual theme override)

• Open user settings JSON: Preferences: Open User Settings (JSON) or edit:
  • Linux: $HOME/.config/Code/User/settings.json
  • macOS: $HOME/Library/Application Support/Code/User/settings.json
  • Windows: %APPDATA%\\Code\\User\\settings.json
• Add or merge:

"editor.tokenColorCustomizations": {
  "textMateRules": [
    {
      "scope": "keyword.control.rule-statement.loci",
      "settings": { "fontStyle": "bold" }
    },
    {
      "scope": "support.function.rule-kind.loci",
      "settings": { "fontStyle": "italic" }
    },
    {
      "scope": "entity.name.function.rule-output.loci",
      "settings": { "foreground": "#ffcc66" }
    },
    {
      "scope": "variable.parameter.rule-input.loci",
      "settings": { "foreground": "#82aaff" }
    }
  ]
}

• Adjust colors to taste. These scopes come from syntaxes/loci.tmlLanguage.json and override your theme for Loci files.

Rule anatomy (quick reference)

• $rule keyword and rule kind (pointwise, singleton, apply, unit, default, optional).
• Rule head: outputs before the rightmost <-, inputs after it; the arrow is highlighted separately.
• Trailing modifiers: option(...), constraint(...); markers like prelude, compute.

Example

$include "flowPsi.lh"

$type solution store<real> ;
$type stop_iter param<int> ;

$rule default(stop_iter) { $stop_iter = 1000 ; }

$rule pointwise(dtcfl<-dtmax) {
  $dtcfl = real($dtmax) ;
}

$rule apply(cl->qresidual<-qdot)[Loci::Summation],
  constraint(cl->geom_cells) {
  join($cl->$qresidual, $qdot) ;
}

Developer info (build, test, package)

• Prereqs: Node.js 20+ (current @vscode/vsce needs the global File API), npm. If you must stay on Node 18, use npx @vscode/vsce@2.21.0 package when packaging.
• Install deps: npm install
• Build once: npm run compile (or npm run watch while developing)
• Run in VS Code: open the folder, press Run and Debug (F5) and pick Run Extension; reload the Extension Development Host after edits. For a faster loop, run npm run watch in the main window while using F5 to reload.
• Package a VSIX (share/install locally):

npm install
npm run compile
npx @vscode/vsce package

• Outputs loci-syntax-<version>.vsix; install via code --install-extension loci-syntax-*.vsix.
• If vsce warns about a missing repository field, add your Git repo URL to package.json or pass --allow-missing-repository.

Contributing

• Adjust scopes in syntaxes/loci.tmlLanguage.json.
• Update language-configuration.json if bracket or comment behavior changes.
• Provide example snippets/screenshots in this README to showcase improvements.

Release Notes

• 0.1.0 — Expand grammar coverage, add language activation, and document install/usage.
• 0.0.1 — Initial scaffold.