# Interpreter & REPL Integration Reliability Specification

## Executive Summary

This specification defines the requirements, test cases, and quality gates necessary to ensure the Ruchy interpreter and REPL are foundationally reliable. Following Toyota Way principles, we "Stop the Line" until these core components meet 100% reliability standards.

## Principle: Jidoka (自働化)

**"Build quality in, don't inspect it in"**

The interpreter and REPL are the foundation of Ruchy. Any defect here cascades to all users. We must:
1. Stop all feature development until reliability is achieved
2. Build comprehensive automated testing
3. Make defects impossible through design
4. Create permanent gates that prevent regression

## Critical Requirements

### 1. Core Functionality (MUST WORK 100%)

#### 1.1 Basic Evaluation
- [ ] Arithmetic operations with correct precedence
- [ ] Variable bindings (let, let mut)
- [ ] Function definitions and calls
- [ ] Recursion with proper tail call optimization
- [ ] Closures and captured variables
- [ ] Lambda expressions

#### 1.2 Data Types
- [ ] Integers (i32, i64 with proper overflow handling)
- [ ] Floats (f32, f64 with NaN/Inf handling)
- [ ] Strings (literals, interpolation, escaping)
- [ ] Booleans
- [ ] Characters
- [ ] Lists/Arrays
- [ ] Tuples
- [ ] Structs (definition and instantiation)
- [ ] Enums (including Option<T> and Result<T,E>)
- [ ] Objects/HashMaps

#### 1.3 Control Flow
- [ ] If/else expressions
- [ ] Match expressions with exhaustiveness
- [ ] For loops (with ranges and iterables)
- [ ] While loops
- [ ] Break/continue
- [ ] Return statements
- [ ] Error propagation (?)

#### 1.4 Advanced Features
- [ ] Pattern matching (destructuring)
- [ ] Pipeline operators (|>)
- [ ] Method calls on primitives
- [ ] String interpolation (f"Hello {name}")
- [ ] Async/await
- [ ] Impl blocks and methods
- [ ] Module system

### 2. REPL-Specific Requirements

#### 2.1 Session Management
- [ ] Variable persistence across inputs
- [ ] Function definition persistence
- [ ] Type/struct/enum definition persistence
- [ ] History management
- [ ] Multi-line input handling
- [ ] Proper scope management

#### 2.2 Error Recovery
- [ ] Syntax errors don't crash REPL
- [ ] Runtime errors don't lose session state
- [ ] Stack overflow protection
- [ ] Memory limit enforcement
- [ ] Timeout protection for infinite loops

#### 2.3 User Experience
- [ ] Tab completion
- [ ] Syntax highlighting
- [ ] Clear error messages with context
- [ ] Help system (:help, :type, etc.)
- [ ] Pretty printing of values

### 3. Integration Requirements

#### 3.1 Transpiler Consistency
- [ ] REPL evaluation matches transpiled code behavior
- [ ] Same type inference rules
- [ ] Same operator precedence
- [ ] Same error messages

#### 3.2 Performance Bounds
- [ ] Sub-100ms response for simple expressions
- [ ] Memory usage < 100MB for typical session
- [ ] Handle 10,000+ line sessions
- [ ] Support recursive depth of 1000+

## Test Suite Specification

### Level 1: Unit Tests (Granular)

```rust
// tests/interpreter/arithmetic.rs
#[test]
fn test_integer_addition() {
    assert_eval!("1 + 2", Int(3));
}

#[test]
fn test_operator_precedence() {
    assert_eval!("2 + 3 * 4", Int(14));
    assert_eval!("(2 + 3) * 4", Int(20));
}

#[test]
fn test_integer_overflow() {
    assert_eval!("9223372036854775807 + 1", Error("Integer overflow"));
}
```

### Level 2: Integration Tests (Feature-Complete)

```rust
// tests/interpreter/functions.rs
#[test]
fn test_recursive_fibonacci() {
    let program = r#"
        fun fib(n) {
            if n <= 1 { n } else { fib(n-1) + fib(n-2) }
        }
        fib(10)
    "#;
    assert_eval!(program, Int(55));
}

#[test]
fn test_closure_capture() {
    let program = r#"
        fun make_adder(x) {
            |y| x + y
        }
        let add5 = make_adder(5)
        add5(3)
    "#;
    assert_eval!(program, Int(8));
}
```

### Level 3: Property-Based Tests

```rust
// tests/interpreter/properties.rs
use quickcheck::quickcheck;

quickcheck! {
    fn prop_arithmetic_commutative(a: i32, b: i32) -> bool {
        eval(&format!("{} + {}", a, b)) == eval(&format!("{} + {}", b, a))
    }
    
    fn prop_function_deterministic(x: i32) -> bool {
        let prog = format!("fun f(x) {{ x * 2 }}; f({})", x);
        let result1 = eval(&prog);
        let result2 = eval(&prog);
        result1 == result2
    }
}
```

### Level 4: Regression Tests

```rust
// tests/interpreter/regressions.rs
// Every bug found becomes a permanent test

#[test]
fn test_issue_001_file_operations_hang() {
    // Bug: File operations would hang in v0.7.7
    let result = eval_with_timeout("readFile('test.txt')", Duration::from_secs(1));
    assert!(result.is_ok() || result == Err(TimeoutError));
}

#[test]
fn test_issue_002_tuple_parsing() {
    // Bug: Tuples failed to parse in REPL
    assert_eval!("(1, 2, 3)", Tuple(vec![Int(1), Int(2), Int(3)]));
}
```

### Level 5: Chaos/Fuzz Testing

```rust
// tests/interpreter/chaos.rs
#[test]
fn test_random_valid_programs() {
    let fuzzer = AstFuzzer::new();
    for _ in 0..10000 {
        let ast = fuzzer.generate_valid_ast();
        let result = eval_ast(&ast);
        assert!(!result.is_crash()); // Should error gracefully, never crash
    }
}

#[test]
fn test_malformed_input() {
    let inputs = vec![
        "(((((((",
        "fun fun fun",
        "let let let",
        "1 + + + 2",
        ";;;;;;;;",
    ];
    for input in inputs {
        assert!(eval(input).is_err()); // Should error, not panic
    }
}
```

## Quality Gates (BLOCKING)

### Pre-Commit Hooks

```bash
#!/bin/bash
# .git/hooks/pre-commit

# GATE 1: Core interpreter tests must pass
cargo test --package ruchy --test interpreter_core || {
    echo "❌ BLOCKED: Core interpreter tests failing"
    exit 1
}

# GATE 2: REPL integration tests must pass
cargo test --package ruchy --test repl_integration || {
    echo "❌ BLOCKED: REPL integration tests failing"
    exit 1
}

# GATE 3: No panic! in interpreter code
! grep -r "panic!" src/runtime/ --include="*.rs" || {
    echo "❌ BLOCKED: panic! found in interpreter"
    echo "Use Result<> instead"
    exit 1
}

# GATE 4: Complexity limit
pmat check src/runtime/ --max-complexity 10 || {
    echo "❌ BLOCKED: Interpreter complexity too high"
    exit 1
}
```

### CI/CD Pipeline

```yaml
name: Interpreter Reliability Gates
on: [push, pull_request]

jobs:
  interpreter-validation:
    runs-on: ubuntu-latest
    strategy:
      matrix:
        test-suite:
          - arithmetic
          - functions
          - control-flow
          - data-types
          - error-handling
          - performance
          
    steps:
      - name: Run Test Suite
        run: |
          cargo test --test ${{ matrix.test-suite }} --no-fail-fast
          
      - name: Benchmark Performance
        run: |
          cargo bench --bench interpreter
          # Fail if performance degrades >5%
          
      - name: Memory Leak Check
        run: |
          valgrind --leak-check=full cargo test
          
      - name: Thread Safety Check
        run: |
          cargo test --features concurrent -- --test-threads=16
```

## Implementation Plan

### Phase 1: Immediate Fixes (Day 1)
1. Fix known interpreter bugs
2. Add missing core functionality
3. Ensure REPL session persistence

### Phase 2: Test Infrastructure (Day 2-3)
1. Implement test macro framework
2. Create comprehensive test suite
3. Add property-based tests
4. Set up continuous benchmarking

### Phase 3: Quality Gates (Day 4)
1. Install pre-commit hooks
2. Configure CI/CD pipeline
3. Add performance regression detection
4. Document reliability metrics

### Phase 4: Validation (Day 5)
1. Run 24-hour stress test
2. Fuzzing campaign
3. Memory leak validation
4. Performance profiling

## Success Criteria

### Mandatory (Gate to Continue)
- [ ] 100% pass rate on core functionality tests
- [ ] Zero panics in 1M random inputs
- [ ] Memory stable over 10K REPL commands
- [ ] <100ms response for 95% of operations
- [ ] 100% backwards compatibility with v0.7.x

### Target Metrics
- Test Coverage: >95% for interpreter code
- Cyclomatic Complexity: <10 for all functions
- Mean Time Between Failures: >100 hours
- Mean Time To Recovery: <1 second
- Error Message Quality: 100% actionable

## Monitoring & Alerting

### Runtime Telemetry
```rust
// Automatically track in REPL
- Command success/failure rate
- Response time percentiles
- Memory usage over time
- Error frequency by type
- Feature usage statistics
```

### Quality Dashboard
```
Interpreter Health: ████████████████████ 100%
├─ Core Ops:       ████████████████████ 100%
├─ Data Types:     ████████████████████ 100%
├─ Control Flow:   ████████████████████ 100%
├─ Error Recovery: ████████████████████ 100%
└─ Performance:    ████████████████████ 100%
```

## Maintenance Protocol

### Daily
- Run full test suite
- Check performance metrics
- Review error logs

### Weekly
- Fuzzing campaign
- Memory profiling
- Update regression tests

### Monthly
- Full reliability audit
- Performance benchmarking
- Documentation update

## Appendix A: Known Issues to Fix

1. **Let binding scope** - Variables defined in let create nested scopes
2. **Transpiler consistency** - REPL behavior differs from transpiled code
3. **Error messages** - Not always actionable or clear
4. **Performance** - No optimization for hot paths
5. **Memory leaks** - Possible in recursive closures

## Appendix B: Test Data Sets

### Ruchy Book Examples
All 259 examples from the Ruchy book must work in REPL

### Standard Library Tests
Every function in std lib must have tests

### Real-World Programs
- Web server
- Data processing pipeline
- Game logic
- Mathematical computations

## Conclusion

The interpreter and REPL are the heart of Ruchy. By implementing this specification, we ensure:
1. **Reliability**: No surprises for users
2. **Performance**: Predictable and fast
3. **Maintainability**: Changes don't break existing code
4. **Trust**: Users can depend on Ruchy

**Remember**: We don't ship until this specification is 100% complete. Quality is built in, not bolted on.