Chester Programming Language

Chester is a statically-typed functional language that compiles to TypeScript, featuring an advanced effect system and seamless JavaScript/TypeScript interoperability.

Warning

Chester is under active development. The language design and implementation are not stable.

Key Features

• TypeScript Backend - Compiles to readable TypeScript code
• Effect System - Track and manage side effects with CPS transformation
• JS/TS Interop - Import npm packages with automatic type extraction
• Multi-Platform - Runs on JVM, JavaScript, and Native
• Developer Tools - REPL, LSP server, IntelliJ plugin, web REPL

Quick Start

Build

sbt cliJVM/assembly

Run

# Start REPL
java -jar modules/cli/jvm/target/scala-3.7.4/cli-assembly-*.jar

# Run a file
java -jar modules/cli/jvm/target/scala-3.7.4/cli-assembly-*.jar hello.chester

# Compile to TypeScript
java -jar modules/cli/jvm/target/scala-3.7.4/cli-assembly-*.jar ts src/ --output dist

For detailed setup, see Getting Started in the documentation.

Documentation

📚 Full documentation is available in the docs/ directory:

• Getting Started - Build and run your first program
• CLI Usage - Command-line interface guide
• Language Guide - Syntax and features
• Development Docs - Internals and architecture

Build Documentation Site

cd docs
./dev.sh build
# or serve locally:
./dev.sh serve

Website (Next.js + pnpm)

The marketing site lives in site/ and uses the latest Next.js and React stack.

cd site
pnpm install
pnpm dev   # start the dev server
pnpm build # production build

You can also run the same commands from sbt:

sbt "site/pnpmDev"   # dev server
sbt "site/pnpmBuild" # production build

REPL bundle (shared CLI logic)

The browser REPL reuses the CLI. Build the Scala.js bundle and copy it into site/public/scala:

sbt webRepl/copyWebRepl

Then run the site (pnpm dev) and open /repl. If the bundle is missing, the page will show an error with the command to build it.

To run the site tests (including the REPL mock), build the bundle first and then:

cd site
pnpm test

Repository Structure

chester/
├── modules/           # Source code
│   ├── cli/          # Command-line interface
│   ├── core/         # Parser, type checker, backends
│   ├── lsp/          # Language Server Protocol
│   ├── utils/        # Shared utilities
│   ├── web-repl/     # Browser REPL (Scala.js)
│   └── intellij-plugin/  # IntelliJ integration
├── site/             # Next.js website
├── docs/             # Documentation (mdbook)
├── vendor/           # Vendored dependencies
└── build.sbt         # Build configuration

See Module Structure for details.

Example

module example;

import "chalk";  // Import npm packages

def greet(name: String): IO Unit = {
  let message = chalk.green("Hello, " ++ name ++ "!");
  println(message)
};

def main: IO Unit = greet("World");

Compile to TypeScript:

chester ts example.chester --output dist

Development

• Language: Scala 3.7.4
• Build Tool: sbt
• Platforms: JVM, JavaScript (Scala.js), Native (Scala Native)

# Compile all modules
sbt compile

# Run tests
sbt test

# Build CLI
sbt cliJVM/assembly

# Build native binary (faster startup)
sbt cliNative/nativeLink

Links

• Previous Version: https://github.com/chester-lang/chester2025draft (IDE plugins are for the previous version)
• Website Domain: https://the-lingo.org/ (subject to change)

License

See LICENSE.md