Closes#26
- Added -i flag to select interpreter (lambda or debruijn)
- Created debruijn package with Expression interface
- Variable contains index and optional label
- Abstraction contains only body (no parameter)
- Application structure remains similar
- Implemented De Bruijn reduction without variable renaming
- Shift operation handles index adjustments
- Substitute replaces by index instead of name
- Abstracted Engine into interface with two implementations
- LambdaEngine: original named variable engine
- DeBruijnEngine: new index-based engine
- Added conversion functions between representations
- LambdaToDeBruijn: converts named to indexed
- DeBruijnToLambda: converts indexed back to named
- SaccharineToDeBruijn: direct saccharine to De Bruijn
- Updated main to switch engines based on -i flag
- All test samples pass with both engines
Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>
