Epsil in Visual Studio Code

The Epsil extension for Visual Studio Code provides language support for .epsil source files:

• Syntax highlighting for the full grammar: nested block comments, string interpolation, multiline and raw strings, verbatim symbols, $…$ LaTeX islands, pragmas, and number literals.
• Live diagnostics as you type: parse errors, lints, and static type errors, reported by the same checker as epsil check.
• Run commands: execute the current file in the integrated terminal with one click.

warning

Epsil and its Visual Studio Code extension are experimental. Their syntax and behavior may change between releases.

Installation

The extension is not yet published to the Visual Studio Code Marketplace. To install it from the repository:

git clone https://github.com/cortex-js/compute-engine.git
cd compute-engine/vscode-epsil
npm install
npm run build
npx @vscode/vsce package
code --install-extension epsil-0.1.0.vsix

Reinstall the .vsix after pulling changes to the extension.

Editing

Opening a file with the .epsil extension activates the language support. Highlighting follows the conventions of the language: capitalized identifiers (Sin, Simplify) are library operators, lowercase identifiers are user symbols, and merely-reserved words are not highlighted as keywords.

Diagnostics appear inline (squiggles) and in the Problems panel. They are the same diagnostics epsil check reports: syntax errors, lints such as zero-index, and the type errors the engine detects when the program is canonicalized. The editor never evaluates your program — checking is static, so a long-running computation in a file does not affect editing.

let radius = 1/2
let area = Pi * radius^2
N(area)

Running

With an Epsil file in the active editor, use the run button (▷) in the editor title bar, or Epsil: Run File from the Command Palette. The file is saved, then executed in an integrated terminal named Epsil, from the workspace folder of the file:

npx epsil program.epsil

The command used is configurable (see below): by default it is npx epsil, which resolves the CLI from the project's installed @cortex-js/compute-engine package.

Commands

Command	Action
Epsil: Run File	Save the active Epsil file and run it in the integrated terminal
Epsil: Restart Language Server	Restart the diagnostics server

Settings

Setting	Default	Purpose
epsil.cliCommand	npx epsil	Command used by Epsil: Run File to execute a source file
epsil.diagnostics.enable	true	Report diagnostics as you type
epsil.trace.server	off	Log the language-server protocol traffic (for debugging)

Settings can be set per workspace. For example, a project that runs Epsil from a local build rather than an installed package can override the run command in its .vscode/settings.json:

{ "epsil.cliCommand": "node ./build/epsil.js" }

Contributing

The extension lives in the vscode-epsil/ directory of the Compute Engine repository. It bundles the engine from source, so changes to the language are picked up by rebuilding the extension. See its README.md for the development workflow (launch configurations for running and debugging the extension and its language server are included), and examples/demo.epsil for a tour of the language support.

Completions, hover documentation, formatting, and notebook support are planned but not yet implemented.