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CLAUDE.md

This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.

Build and Development Commands

make run        # Build and run Ghost REPL
make build      # Build for all platforms (mac/linux/windows)
make test       # Run all tests with colored output
go test -v ./evaluator/...  # Run tests for a specific package

Architecture Overview

Ghost is a tree-walking interpreter written in Go. The execution pipeline follows this flow:

Source Code → Scanner → Parser → AST → Evaluator → Object

Core Packages

  • scanner/ - Lexical analysis. Transforms source into tokens. Keywords defined in scanner/scanner.go:21-48.
  • token/ - Token type definitions and the Token struct containing lexeme, literal, position info.
  • parser/ - Recursive descent parser using Pratt parsing. Each AST node type has its own parsing function (e.g., parser/function.go, parser/if.go).
  • ast/ - Abstract syntax tree node definitions. Base interfaces in ast/ast.go: Node, StatementNode, ExpressionNode.
  • evaluator/ - Tree-walking evaluation. Main entry point is Evaluate() in evaluator/evaluator.go:15. Each AST node type has a corresponding evaluate* function.
  • object/ - Runtime value types (Number, String, Boolean, List, Map, Function, Class, etc.). The Object interface (object/object.go:15-19) requires Type(), String(), and Method().
  • ghost/ - Main Ghost struct that orchestrates the pipeline (ghost/ghost.go). Entry point for embedding Ghost in Go applications.

Key Design Patterns

  • Scope: Wraps Environment and tracks Self for method calls (object/scope.go).
  • Environment: Variable storage with parent chain for lexical scoping (object/environment.go).
  • Library system: Native functions and modules registered via library.RegisterFunction() and library.RegisterModule(). Built-in modules in library/modules/.

Object Method System

All object types implement the Method(method string, args []Object) (Object, bool) interface. Methods are defined directly on object types (e.g., string methods in object/string.go).

Language Features

Ghost supports: classes with inheritance (extends), traits (trait/use), first-class functions, closures, lists, maps, for/for-in/while loops, switch statements, imports, and compound operators (+=, ++, etc.).

Version

Update version/version.go when releasing. GoReleaser handles binary distribution.