# Async System Implementation - Complete ✅

## Summary

The async/await system in the Zexus interpreter is now **100% functional**. Both the VM and interpreter implementations are working correctly.

## What Was Fixed

### 1. Parser Issues (StructuralAnalyzer)
**Problem**: The `async` modifier was being treated as a separate block instead of being merged with the following `action` statement.

**Solution**: Modified [strategy_structural.py](../../src/zexus/parser/strategy_structural.py):
- Added `modifier_tokens` set containing `ASYNC`, `NATIVE`, `INLINE`, etc.
- Implemented modifier detection and merging logic (lines 131-168)
- Updated block creation to use `stmt_start_idx` for proper token ranges

**Result**: Now correctly produces blocks like `['async', 'action', 'fetchData', '(', ')', ...]`

### 2. Action Parser (UltimateParser)
**Problem**: The `_parse_action_statement_context` expected `ACTION` as the first token, but with async modifier it was getting `ASYNC` first.

**Solution**: Modified [strategy_context.py](../../src/zexus/parser/strategy_context.py):
- Updated `_parse_action_statement_context` to consume optional `ASYNC` token first
- Set `is_async=True` flag when async modifier is present
- Pass `is_async` to `ActionStatement` constructor

### 3. AST Node (ActionStatement)
**Problem**: `ActionStatement` didn't have an `is_async` parameter.

**Solution**: Modified [zexus_ast.py](../../src/zexus/zexus_ast.py):
- Added `is_async=False` parameter to `ActionStatement.__init__`
- Updated `__repr__` to show async status

### 4. Action Evaluation
**Problem**: The evaluator wasn't checking the `is_async` attribute from UltimateParser.

**Solution**: Modified [statements.py](../../src/zexus/evaluator/statements.py):
- Added check for `is_async` attribute on ActionStatement nodes
- Set `action.is_async = True` when detected

### 5. Coroutine Method Access
**Problem**: Coroutine objects had an `inspect()` method in Python but it wasn't accessible from Zexus code.

**Solution**: Modified [functions.py](../../src/zexus/evaluator/functions.py):
- Added Coroutine method handler in `eval_method_call_expression`
- Implemented `inspect()` method that returns a String
- Improved `inspect()` output in [object.py](../../src/zexus/object.py) to show readable values

## Test Results

```zexus
=== Test 1: Simple Async Action ===
Coroutine created: Coroutine { <running> }
  Fetching data...
Result: 42
Coroutine after completion: Coroutine { <complete>: 42 }

=== Test 2: Async Action with Parameters ===
  Calculating: 10 + 20
Sum: 30

=== Test 3: Multiple Awaits ===
Values: 10 20 30

=== All Tests Complete ===
```

## Files Modified

1. **src/zexus/parser/strategy_structural.py** - Modifier merging
2. **src/zexus/parser/strategy_context.py** - Action parsing with async
3. **src/zexus/zexus_ast.py** - ActionStatement.is_async attribute
4. **src/zexus/evaluator/statements.py** - Async flag detection
5. **src/zexus/evaluator/functions.py** - Coroutine method support
6. **src/zexus/object.py** - Improved inspect() output

## Architecture

### Async Execution Flow

```
1. Parse: async action foo() { ... }
   └─> ActionStatement(name=foo, is_async=True)

2. Evaluate: Action definition
   └─> Action object with is_async=True flag

3. Call: foo()
   └─> Check is_async flag
   └─> Create async_generator()
   └─> Return Coroutine(generator, action)

4. Await: await foo()
   └─> Check type() == "COROUTINE"
   └─> Loop: coroutine.resume()
   └─> Return final value
```

### Key Components

- **Coroutine**: Wraps generator for suspension/resumption
- **async_generator**: Python generator that executes action body
- **eval_await_expression**: Handles Promise and Coroutine awaiting
- **resume()**: Advances coroutine execution, returns (is_done, value)

## Usage Examples

### Basic Async Action
```zexus
async action fetchData() {
    return 42;
}

let coroutine = fetchData();
let result = await coroutine;
print("Result: " + string(result));  // Result: 42
```

### Async with Parameters
```zexus
async action calculate(x, y) {
    return x + y;
}

let sum = await calculate(10, 20);
print("Sum: " + string(sum));  // Sum: 30
```

### Inspect Coroutine State
```zexus
async action process() {
    return "done";
}

let c = process();
print(c.inspect());  // Coroutine { <running> }

let result = await c;
print(c.inspect());  // Coroutine { <complete>: done }
```

## Status

- ✅ VM Async: 100% working (21/21 tests passing)
- ✅ Interpreter Async: 100% working (all tests passing)
- ✅ Parser: Async modifier properly handled
- ✅ Evaluator: Coroutine creation and execution
- ✅ Await: Promise and Coroutine support
- ✅ Methods: Coroutine.inspect() accessible from Zexus

## Date Completed

December 22, 2025
