User-Defined Functions Implementation Plan

Overview

Implement user-defined functions in XMD following the blueprint’s shell-style syntax and natural language principles.

Target Syntax (from Blueprint)

// Natural/Mobile syntax:
function add a b
    return a + b

// Usage
result = add 10 20

Current State Analysis

  • ✅ AST_FUNCTION_CALL exists for calling built-in functions (exec, join, import)
  • ❌ No AST_FUNCTION_DEF for defining user functions
  • ❌ No function storage/lookup mechanism
  • ❌ No function scope/parameter handling
  • ❌ No return statement processing

Implementation Phases

Phase 1: Core AST Extensions

  • Add AST_FUNCTION_DEF node type
  • Add function definition parsing
  • Add function storage in evaluator context
  • Basic function call resolution

Phase 2: Parameter & Scope Management

  • Parameter binding and local scope
  • Return statement handling
  • Function-local variable isolation

Phase 3: Advanced Features

  • Default parameters
  • Variable arguments
  • Recursive functions
  • Function overloading

Phase 4: Integration & Testing

  • Shell-style syntax transformation
  • Comprehensive test suite
  • Documentation update

Success Criteria

  1. Parse function name param1 param2 syntax
  2. Store functions in evaluator context
  3. Call user functions with name arg1 arg2 syntax
  4. Proper parameter binding and scope isolation
  5. Return values correctly
  6. Support recursion
  7. All tests pass

Next Steps

Start with Phase 1 implementation.