Lumen is a small dynamically-typed scripting language implemented in Kotlin. Source is scanned into tokens, parsed into an abstract syntax tree, compiled to a compact bytecode representation, and executed on a stack-based virtual machine.

Features

First-class functions and closures that capture mutable state
let / var bindings with lexical scoping
Control flow: if / else, while, and for ... in loops
Lists and maps with literal syntax and built-in methods
String, list, and map methods plus a small numeric standard library
A module system driven by import for splitting programs across files
Built-ins such as print, println, len, type, str, int, assert, map, filter, and reduce
An interactive REPL and a file runner

Building

The project uses the Gradle wrapper, so no local Gradle install is required:

./gradlew build

Running

Start the REPL:

./gradlew run

Run a program file:

./gradlew run --args="examples/fib.lumen"

Disassemble the compiled bytecode for a file:

./gradlew run --args="--dump examples/fib.lumen"

Example

fn makeCounter() {
    var count = 0
    fn increment() {
        count = count + 1
        return count
    }
    return increment
}

let counter = makeCounter()
println(counter(), counter(), counter())

let numbers = [1, 2, 3, 4, 5]
let doubled = map(fn(x) { return x * 2 }, numbers)
println(doubled)

More programs live in examples/, including a reverse-polish calculator, closures, sorting, CSV handling, and reusable library modules under examples/lib/.

Project layout

src/main/kotlin/lumen/
  lexer/      token definitions and the tokenizer
  ast/        abstract syntax tree nodes
  parser/     recursive descent parser
  bytecode/   opcodes, chunk container, and disassembler
  compiler/   AST to bytecode compiler
  runtime/    runtime value model
  vm/         virtual machine, builtins, methods, and standard library
  module/     module loader and import resolution
  cli/        REPL and command-line entry point
src/test/kotlin/lumen/   test suite
examples/                sample Lumen programs

Tests

./gradlew test