feat: add De Bruijn index reduction engine #27

mvhutz · 2026-01-13T02:28:00Z

mvhutz commented

2026-01-13 02:28:00 +00:00

Summary

Adds -i flag to select interpreter (lambda or debruijn)
Implements De Bruijn index-based reduction engine that eliminates variable renaming
Abstracts Engine into interface with LambdaEngine and DeBruijnEngine implementations
Adds conversion functions between lambda calculus and De Bruijn representations
All test samples pass with both engines

Implementation Details

De Bruijn Package

Variable: Contains integer index and optional label string
Abstraction: Contains only body (no parameter needed)
Application: Similar structure to lambda version
Substitute: Replaces variables by index with automatic shift operations
ReduceAll: Mirrors lambda reduction without variable renaming overhead

Engine Abstraction

Created Engine interface with Run() and GetResult() methods
LambdaEngine: Original named variable implementation
DeBruijnEngine: New index-based implementation
Both engines support all existing features (profiling, statistics, explanation, verbose mode)

Conversion Functions

LambdaToDeBruijn: Converts named lambda expressions to De Bruijn indices
DeBruijnToLambda: Converts De Bruijn indices back to named expressions
SaccharineToDeBruijn: Direct conversion from saccharine syntax to De Bruijn

Testing

Added comprehensive test suite comparing both engines
All 6 test files pass (thunk, comments, church_5^5, church_6^6, list_2^30, fast_list_2^30)
De Bruijn engine produces correct reductions without variable conflicts

Test Plan

Build succeeds
All existing tests pass with lambda engine (default)
All existing tests pass with debruijn engine (-i debruijn)
Invalid interpreter flag returns error
Both engines produce equivalent reduced forms
Performance profiling works with both engines
Statistics tracking works with both engines
Verbose mode works with both engines

Closes #26

## Summary - Adds `-i` flag to select interpreter (lambda or debruijn) - Implements De Bruijn index-based reduction engine that eliminates variable renaming - Abstracts Engine into interface with LambdaEngine and DeBruijnEngine implementations - Adds conversion functions between lambda calculus and De Bruijn representations - All test samples pass with both engines ## Implementation Details ### De Bruijn Package - **Variable**: Contains integer index and optional label string - **Abstraction**: Contains only body (no parameter needed) - **Application**: Similar structure to lambda version - **Substitute**: Replaces variables by index with automatic shift operations - **ReduceAll**: Mirrors lambda reduction without variable renaming overhead ### Engine Abstraction - Created `Engine` interface with `Run()` and `GetResult()` methods - `LambdaEngine`: Original named variable implementation - `DeBruijnEngine`: New index-based implementation - Both engines support all existing features (profiling, statistics, explanation, verbose mode) ### Conversion Functions - `LambdaToDeBruijn`: Converts named lambda expressions to De Bruijn indices - `DeBruijnToLambda`: Converts De Bruijn indices back to named expressions - `SaccharineToDeBruijn`: Direct conversion from saccharine syntax to De Bruijn ### Testing - Added comprehensive test suite comparing both engines - All 6 test files pass (thunk, comments, church_5^5, church_6^6, list_2^30, fast_list_2^30) - De Bruijn engine produces correct reductions without variable conflicts ## Test Plan - [x] Build succeeds - [x] All existing tests pass with lambda engine (default) - [x] All existing tests pass with debruijn engine (`-i debruijn`) - [x] Invalid interpreter flag returns error - [x] Both engines produce equivalent reduced forms - [x] Performance profiling works with both engines - [x] Statistics tracking works with both engines - [x] Verbose mode works with both engines Closes #26

mvhutz added 1 commit 2026-01-13 02:28:00 +00:00

feat: add De Bruijn index reduction engine f3b9137d75

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>

mvhutz closed this pull request

2026-01-17 00:27:26 +00:00

Pull request closed

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Reference: mvhutz/lambda#27