# Future Compiler Design Documentation

This directory contains design documents for a **future BASIC compiler** with advanced optimizations. These features are **NOT implemented** in the current MBASIC interpreter.

## Important Notice

⚠️ **These are design documents only** - The current mbasic project is a **runtime interpreter**, not a compiler. These documents describe potential future work for a compiler that would generate optimized native code.

## What's Here

### Semantic Analysis & Optimization Design

**SEMANTIC_ANALYSIS_DESIGN.md** (formerly ACCOMPLISHMENTS.md)
- Comprehensive design for semantic analyzer with 18 optimizations
- Type inference, constant folding, dead code elimination
- Loop analysis, strength reduction, common subexpression elimination
- This was originally labeled as "accomplishments" but describes unimplemented compiler features

**SEMANTIC_ANALYZER.md**
- Detailed semantic analyzer implementation plan
- Symbol tables, type checking, scope analysis
- Integration with optimization passes

**OPTIMIZATION_STATUS.md**
- Status of 27 planned compiler optimizations
- Implementation strategies for each optimization
- Dependencies and priority levels

**optimization_guide.md**
- User guide for compiler optimizations
- How to enable/disable specific optimizations
- Performance impact analysis

**README_OPTIMIZATIONS.md**
- Overview of the optimization suite
- Architecture and design principles

### Type System Optimizations

**TYPE_REBINDING_STRATEGY.md** (Phase 1)
- Strategy for optimizing variable type changes
- Detecting when variables change types
- Code generation for type rebinding

**TYPE_REBINDING_PHASE2_DESIGN.md** (Phase 2)
- Type promotion analysis (INTEGER → DOUBLE)
- Detection of mixed-type expressions
- Safe promotion tracking

**TYPE_REBINDING_IMPLEMENTATION_SUMMARY.md**
- Implementation summary of type rebinding phases
- Test results and performance analysis

**TYPE_INFERENCE_WITH_ERRORS.md**
- Type inference in presence of error handling
- ON ERROR GOTO impact on type analysis

**DYNAMIC_TYPE_CHANGE_PROBLEM.md**
- Analysis of BASIC's dynamic typing challenges
- Solutions for compiler optimization

### Integer Size Optimization

**INTEGER_SIZE_INFERENCE.md**
- 8/16/32-bit integer size optimization
- Massive performance gains on 8-bit CPUs (10-20x faster)
- Detection of optimal integer sizes from ranges

**INTEGER_INFERENCE_STRATEGY.md**
- Strategy for inferring integer sizes
- FOR loop analysis, string function returns
- Signed vs unsigned integer tracking

### Iterative Optimization Framework

**ITERATIVE_OPTIMIZATION_STRATEGY.md**
- Multi-pass optimization strategy
- Fixed-point convergence for optimization phases
- Dependency analysis between optimizations

**ITERATIVE_OPTIMIZATION_IMPLEMENTATION.md**
- Implementation of iterative optimization framework
- Convergence detection and termination
- Performance and correctness validation

**OPTIMIZATION_DATA_STALENESS_ANALYSIS.md**
- Analysis of when optimization data becomes stale
- Invalidation strategies for optimization passes

### Compilation Strategies

**COMPILATION_STRATEGIES_COMPARISON.md**
- Comparison of different compilation approaches
- Trade-offs between code size and performance
- Target architecture considerations

**COMPILER_SEMANTIC_ANALYSIS_SESSION.md** (formerly SESSION_SUMMARY.md)
- Session notes on semantic analysis implementation
- Design decisions and rationale

### Runtime System Design

**STRING_ALLOCATION_AND_GARBAGE_COLLECTION.md**
- CP/M era MBASIC string memory management
- Original 8080 garbage collection algorithm (O(n²))
- Requirements for 8080-compatible compiler backend
- Historical analysis of string heap and descriptor format

## Why These Aren't Implemented

The current mbasic project is a **faithful interpreter** for MBASIC 5.21, providing:
- Runtime compatibility with original CP/M BASIC programs
- Dynamic typing as in original MBASIC
- Interactive REPL mode
- Direct execution without compilation

These compiler optimizations would require:
- Static analysis at "compile time"
- Type inference across the entire program
- Code generation to native or intermediate code
- Loss of some dynamic features (type changes, runtime DIM, etc.)

## Future Work

If a compiler is developed for mbasic, these documents provide:
- Comprehensive optimization strategies
- Detailed implementation plans
- Test cases and validation approaches
- Performance analysis frameworks

The designs are well thought out and ready for implementation when/if a compiler is built.

## Related Documentation

See also in the main doc/ directory:
- **COMPILER_DESIGN.md** - Analysis of compiler vs interpreter differences
- **COMPILER_VS_INTERPRETER_DIFFERENCES.md** - Detailed comparison
- **LANGUAGE_CHANGES.md** - BASIC language evolution

## Status

**All documents in this directory**: Design/planning phase only
**Implementation status**: Not started (interpreter focus)
**Priority**: Future work (after interpreter is complete and stable)
