Lockhart

Lockhart is a bytecode interpreter for a small dynamically-typed language, written in Rust. Source is lexed, parsed into an AST, compiled to bytecode, and executed on a stack-based VM with mark-and-sweep GC.

Current Status

Core language features are implemented with 34 tests covering lexer, parser, codegen, and VM integration. The compiler uses a three-phase pipeline: parse → AST → codegen.

Implemented Language Features

• Numeric literals and arithmetic: +, -, *, /
• Comparisons and equality: >, <, >=, <=, ==, !=
• Boolean and nil literals: true, false, nil
• Logical operators: and, or, !
• String literals and string concatenation with +
• Variable declarations and assignment: let x = ...;, x = ...;
• Blocks and lexical scopes: { ... }
• Control flow: if/else, while, for
• Function declarations and function calls
• return in functions
• print statements

Project Structure

src/
  ast/          # AST node types, spans, pretty-printer
  parser/       # Pratt expression parser + recursive-descent statements
  codegen/      # AST → bytecode lowering
  compiler.rs   # compile() facade (parse → codegen)
  lexer.rs      # tokenization
  vm.rs         # bytecode execution
  gc.rs         # mark/sweep GC + string interning
  table.rs      # hash table (globals, intern table)
  value.rs      # runtime value model
  object.rs     # heap objects (strings, functions)
docs/           # architecture and component documentation

Build

cargo build

Run

REPL:

cargo run

Execute a file:

cargo run -- path/to/file.lh

Dump AST (tree or JSON):

cargo run -- --dump-ast test.lh
cargo run -- --dump-ast --format json test.lh

Example:

fn add(a, b) {
  return a + b;
}

let x = add(2, 3);
print x;

Test

cargo test

Documentation

Architecture overview and component docs live in docs/:

• architecture.md — pipeline, module map, design decisions
• ast.md — AST nodes, spans, dump tooling
• ast-migration.md — future AST roadmap
• compiler.md — parser and codegen
• Additional component docs: lexer, tokens, bytecode, vm, runtime, gc, entry-points

Notes

• Parse errors return structured ParseError with line numbers.
• Codegen errors return CompileError; both map to InterpretCompileError at the VM boundary.
• See docs/ast-migration.md for planned AST improvements.