# BUG-002: Function Definitions Cannot Be Executed

## Ticket Information
- **ID**: BUG-002
- **Priority**: P0 - CRITICAL
- **Severity**: HIGH
- **Component**: Interpreter/Runtime
- **Reported**: 2025-08-26
- **Reporter**: Book Integration Testing
- **Status**: OPEN

## Problem Statement
While the parser successfully generates AST for function definitions using the `fun` keyword, the interpreter fails to execute files containing function definitions with "Failed to parse input" error.

## Impact
- All function-based examples fail
- Blocks ~40+ examples across multiple chapters
- Core language feature non-functional

## Symptoms
```bash
# Parse works:
$ ruchy parse test.ruchy  # SUCCESS - generates correct AST

# Execution fails:
$ ruchy test.ruchy
Error at line: fun add(x, y) {
  Failed to parse input
```

## Reproduction Steps
1. Create file with function:
```ruchy
fun add(x, y) {
    x + y
}
add(10, 20)
```
2. Run: `ruchy test.ruchy`
3. Observe "Failed to parse input" error

## Expected Behavior
- Function should be defined and callable
- `add(10, 20)` should return 30

## Actual Behavior
- Parser generates correct AST
- Interpreter fails with parse error
- Disconnect between parser and interpreter

## Root Cause Hypothesis
- Interpreter may be using different parser configuration
- Function evaluation logic may be incomplete
- Environment handling for functions may be broken

## Acceptance Criteria
- [ ] Functions can be defined and called
- [ ] Both `fun` and `fn` syntax work
- [ ] Recursive functions work
- [ ] Closures work correctly
- [ ] All function test cases pass

## Technical Notes
- Check interpreter's parse_and_eval flow
- Verify function storage in environment
- Test function call evaluation logic