# VM Integration Status Report

## Executive Summary

✅ **VM is available and functional** - All 141 VM tests pass (100%)  
⚠️ **VM is NOT being used by the interpreter** - Bytecode compiler is incomplete

## Investigation Results

### VM Availability
- ✅ VM module imports successfully
- ✅ VM instance can be created
- ✅ JIT compiler is available
- ✅ All VM opcodes implemented and tested

### Evaluator Integration
- ✅ Evaluator has `use_vm` parameter
- ✅ Evaluator creates VM instance during initialization
- ✅ VM statistics tracking is in place
- ✅ Fallback mechanism works correctly

### Compilation Process
- ❌ Bytecode compiler is INCOMPLETE
- ❌ Cannot compile common statements (PrintStatement, etc.)
- ❌ Has errors in handling expressions (AssignmentExpression)

## Conditions for VM Usage

The interpreter will use the VM when **ALL** of these conditions are met:

### 1. VM Must Be Enabled
```python
evaluator = Evaluator(use_vm=True)  # ✅ Working
```

### 2. VM Module Must Be Available
```python
VM_AVAILABLE = True  # ✅ Working
```

### 3. Node Must Meet Heuristics
The `should_use_vm_for_node()` function returns True for:
- ✅ WhileStatement (always)
- ✅ ForEachStatement (always)
- ✅ ActionStatement with >5 body statements
- ✅ Program with >10 statements

### 4. Bytecode Compiler Must Support The Node
```python
bytecode_compiler.can_compile(node)  # ❌ FAILING
```

**This is the blocker!**

## Current Execution Flow

```
1. Parse code → Program AST
2. Check: should_use_vm(program)? → YES (26 statements > 10)
3. Try: bytecode_compiler.compile(program)
4. Result: FAILURE
   Errors:
   - "Unsupported node type for bytecode: PrintStatement"
   - "Compilation error: 'AssignmentExpression' object has no attribute 'target'"
5. Fallback: Direct interpretation (tree-walking)
```

## Test Results

### VM Direct Usage (bypassing interpreter)
```
✅ 141/141 tests passing (100%)
✅ All opcodes working
✅ Async/await functional
✅ Stack operations correct
✅ Control flow working
```

### Interpreter → VM Integration
```
❌ 0% VM usage
❌ 100% direct interpretation
⚠️  Bytecode compilation failures for:
   - PrintStatement
   - LetStatement (assignment expressions)
   - Possibly other statement types
```

## VM Statistics from Test Run

```
Bytecode Compilations: 0
VM Executions:         0
VM Fallbacks:          1
Direct Evaluations:    1

VM Usage: 0.0%
```

## What's Missing?

The **EvaluatorBytecodeCompiler** needs to support:

1. **PrintStatement** - Convert to bytecode
2. **LetStatement** - Handle variable declarations
3. **AssignmentExpression** - Fix attribute access (target vs name)
4. **CallExpression** - Function/action calls
5. **InfixExpression** - Arithmetic operations
6. **All other AST node types** used in typical Zexus programs

## Current State

### What Works
- ✅ VM engine (100% functional)
- ✅ VM integration architecture
- ✅ Heuristics for VM selection
- ✅ Fallback mechanism
- ✅ Statistics tracking

### What Doesn't Work
- ❌ Bytecode compiler (incomplete)
- ❌ AST → Bytecode translation
- ❌ Actual VM execution in production code

## Conclusion

The Zexus interpreter has a **fully functional VM** but **doesn't use it** because the bytecode compiler can't translate AST nodes to bytecode. The interpreter falls back to direct tree-walking interpretation for all code.

### To Enable VM Usage

You would need to implement the missing bytecode compilation logic in `src/zexus/evaluator/bytecode_compiler.py` to handle all AST node types.

### Current Recommendation

The interpreter is working correctly with direct interpretation. The VM is available for when/if the bytecode compiler is completed, but for now, all code execution happens via the tree-walking evaluator.

---

**Date:** December 22, 2025  
**VM Tests:** 141/141 passing  
**VM Usage:** 0% (bytecode compiler incomplete)  
**Fallback:** 100% tree-walking interpretation
