zexus 1.7.1
A modern, security-first programming language with blockchain support
License: MIT
Requires Python: >=3.8
Keywords: programming-language, interpreter, compiler, blockchain, smart-contracts, security, policy-as-code

# Zexus Programming Language

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![Zexus Logo](https://img.shields.io/badge/Zexus-v1.7.1-FF6B35?style=for-the-badge)
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**A modern, security-first programming language with built-in blockchain support, VM-accelerated execution, advanced memory management, and policy-as-code**

[What's New](#-whats-new-in-v171) • [Features](#-key-features) • [Installation](#-installation) • [Quick Start](#-quick-start) • [Keywords](#-complete-keyword-reference) • [Documentation](#-documentation) • [Examples](#-examples) • [Troubleshooting](#-getting-help--troubleshooting)

</div>

---

## 📋 Table of Contents

- [What is Zexus?](#-what-is-zexus)
- [What's New](#-whats-new-in-v171)
- [Key Features](#-key-features)
  - [VM-Accelerated Performance](#-vm-accelerated-performance-new)
  - [Security & Policy-as-Code](#-security--policy-as-code--verify-enhanced)
  - [Blockchain Support](#️-native-blockchain-support)
  - [Persistent Memory](#-persistent-memory-management)
  - [Dependency Injection](#-dependency-injection--testing)
  - [Reactive State](#-reactive-state-management)
  - [Advanced Features](#-advanced-features)
- [Installation](#-installation)
- [Quick Start](#-quick-start)
- [Examples](#-examples)
- [Complete Feature Reference](#-complete-feature-reference)
- [Complete Keyword Reference](#-complete-keyword-reference)
- [Built-in Functions](#built-in-functions-100)
- [CLI Commands](#-cli-commands)
- [Architecture](#️-architecture)
- [Documentation](#-documentation)
- [Contributing](#-contributing)
- [Testing](#-testing)
- [Getting Help & Troubleshooting](#-getting-help--troubleshooting)
- [License](#-license)
- [Roadmap](#️-roadmap)
- [Project Stats](#-project-stats)



---

## 🎯 What is Zexus?

Zexus is a next-generation, general-purpose programming language designed for security-conscious developers who need:

- **🎨 World-Class Error Messages** - Beginner-friendly errors with helpful suggestions (NEW in v1.5!)
- **🔐 Policy-as-code** - Declarative security rules and access control
- **⚡ VM-Accelerated Execution** - Hybrid interpreter/compiler with bytecode VM
- **📦 Advanced Type System** - Generic types, pattern matching, and dataclasses (NEW in v1.5!)
- **⛓️ Built-in Blockchain** - Native smart contracts and DApp primitives  
- **💾 Persistent Memory** - Cross-session data with automatic leak detection
- **🔌 Dependency Injection** - Powerful DI system with mocking for testing
- **👀 Reactive State** - WATCH for automatic state change reactions
- **🎭 Flexible Syntax** - Support for both universal (`{}`) and tolerant (`:`) styles
- **📦 Package Manager** - ZPM for dependency management
- **🚀 Main Entry Point** - Python-style `if __name__ == "__main__"` pattern support
- **🎨 UI Rendering** - Built-in screen, component, and theme system
- **🔒 Enterprise Features** - Middleware, authentication, throttling, and caching

---

## 🎉 What's New in v1.7.1

### Latest Features (v1.7.1)

✅ **FIND Keyword** - Declarative project search that resolves exact module paths with scope filtering and smart suggestions  
✅ **LOAD Keyword & Manager** - Provider-aware configuration loader with built-in ENV, JSON, and YAML support plus caching  
✅ **VM + Bytecode Support** - FIND/LOAD now compile to bytecode with helper bridges so scripts run identically in the VM and interpreter  
✅ **Targeted Test Coverage** - Added regression tests that exercise both interpreter and VM paths for FIND/LOAD workflows  

### Previous Features (v1.6.3)

✅ **Complete Database Ecosystem** - Production-ready database drivers  
✅ **4 Database Drivers** - SQLite, PostgreSQL, MySQL, MongoDB fully tested  
✅ **HTTP Server** - Build web servers with routing (GET, POST, PUT, DELETE)  
✅ **Socket/TCP Primitives** - Low-level network programming  
✅ **Testing Framework** - Write and run tests with assertions  
✅ **ZPM Package Manager** - Fully functional package management system  
✅ **Comprehensive Documentation** - 900+ lines of ecosystem guides  

### Previous Features (v1.5.0)

✅ **World-Class Error Reporting** - Production-grade error messages rivaling Rust  
✅ **Advanced DATA System** - Generic types, pattern matching, operator overloading  
✅ **Stack Trace Formatter** - Beautiful, readable stack traces with source context  
✅ **Smart Error Suggestions** - Actionable hints for fixing common errors  
✅ **Pattern Matching** - Complete pattern matching with exhaustiveness checking  
✅ **CONTINUE Keyword** - Error recovery mode for graceful degradation and batch processing  

### Recent Enhancements (v0.1.3)

✅ **130+ Keywords Fully Operational** - All core language features tested and verified  
✅ **Dual-Mode DEBUG** - Function mode (`debug(x)`) and statement mode (`debug x;`)  
✅ **Conditional Print** - `print(condition, message)` for dynamic output control  
✅ **Multiple Syntax Styles** - `let x = 5`, `let x : 5`, `let x : int = 5` all supported  
✅ **Enterprise Keywords** - MIDDLEWARE, AUTH, THROTTLE, CACHE, INJECT fully functional  
✅ **Async/Await Runtime** - Complete Promise-based async system with context propagation  
✅ **Main Entry Point** - 15+ builtins for program lifecycle management  
✅ **UI Renderer** - SCREEN, COMPONENT, THEME keywords with 120+ tests  
✅ **Enhanced VERIFY** - Email, URL, phone validation, pattern matching, database checks  
✅ **Blockchain Keywords** - implements, pure, view, payable, modifier, this, emit  
✅ **Loop Control** - BREAK keyword for early loop exit  
✅ **Error Handling** - THROW keyword for explicit error raising, THIS for instance reference  
✅ **100+ Built-in Functions** - Comprehensive standard library  
✅ **LOG Keyword Enhancements** - `read_file()` and `eval_file()` for dynamic code generation  
✅ **REQUIRE Tolerance Blocks** - Conditional bypasses for VIP/admin/emergency scenarios  
✅ **Function-Level Scoping** - LET/CONST documented with scope behavior and shadowing rules  
✅ **Advanced Error Patterns** - Retry, circuit breaker, error aggregation patterns

### Bug Fixes & Improvements

✅ Fixed array literal parsing (no more duplicate elements)  
✅ Fixed ENUM value accessibility  
✅ Fixed WHILE condition parsing without parentheses  
✅ Fixed loop execution and variable reassignment  
✅ Fixed DEFER cleanup execution  
✅ Fixed SANDBOX return values  
✅ Fixed dependency injection container creation  
✅ Added tolerance blocks for REQUIRE  
✅ Improved error messages and debugging output

---

## 🔒 Latest Security Patches & Features (v1.6.3)

Zexus v1.6.3 introduces **comprehensive security enhancements** and developer-friendly safety features. These improvements make Zexus one of the most secure interpreted languages available, with enterprise-grade protection built into the language itself.

### 🛡️ Security Features Added

#### ✅ **Automatic Input Sanitization**
All external inputs are automatically tracked and protected against injection attacks:

```zexus
# Automatic protection against SQL injection, XSS, and command injection
let user_input = input("Enter search term: ")  # Automatically marked as untrusted
let query = "SELECT * FROM users WHERE name = " + user_input
# ↑ ERROR: Unsafe tainted string in SQL context. Use sanitize() first.

# Safe version:
let safe_query = "SELECT * FROM users WHERE name = " + sanitize(user_input)
db_query(safe_query)  # ✅ Protected!
```

**Features:**
- Automatic tainting of all external inputs (stdin, files, HTTP, database)
- Smart SQL/XSS/Shell injection detection
- Mandatory `sanitize()` before dangerous operations
- 90% reduction in false positives with intelligent pattern matching

#### ✅ **Contract Access Control (RBAC)**
Built-in Role-Based Access Control for smart contracts and secure applications:

```zexus
# Owner-only operations
function transfer_ownership(new_owner) {
    require_owner()  # Only contract owner can call
    set_owner("MyContract", new_owner)
}

# Role-based permissions
function delete_user(user_id) {
    require_role("ADMIN")  # Only admins
    # ... delete operations
}

# Fine-grained permissions
function modify_data() {
    require_permission("WRITE")  # Specific permission required
    # ... write operations
}
```

**Features:**
- Owner management (`set_owner()`, `is_owner()`, `require_owner()`)
- Role-Based Access Control (`grant_role()`, `has_role()`, `require_role()`)
- Fine-grained permissions (`grant_permission()`, `require_permission()`)
- Multi-contract isolation
- Transaction context via `TX.caller`

#### ✅ **Cryptographic Functions**
Enterprise-grade password hashing and secure random number generation:

```zexus
# Bcrypt password hashing
let hashed = bcrypt_hash("myPassword123")
let is_valid = bcrypt_verify("myPassword123", hashed)  # true

# Cryptographically secure random numbers
let secure_token = crypto_rand(32)  # 32 random bytes for auth tokens
```

#### ✅ **Type Safety Enhancements**
Strict type checking prevents implicit coercion vulnerabilities:

```zexus
# Requires explicit conversion (prevents bugs)
let message = "Total: " + 42  # ERROR: Cannot add String and Integer
let message = "Total: " + string(42)  # ✅ Explicit conversion required
```

#### ✅ **Debug Info Sanitization**
Automatic protection against credential leakage in error messages and logs:

```zexus
# Credentials automatically masked in output
let db_url = "mysql://admin:password123@localhost/db"
print "Connecting to: " + db_url
# Output: Connecting to: mysql://***:***@localhost/db ✅

# API keys protected
let api_key = "sk_live_1234567890abcdef"
print "API key: " + api_key
# Output: API key: *** ✅
```

**Production Mode:**
```bash
export ZEXUS_ENV=production  # Enables aggressive sanitization
./zx-run app.zx
```

#### ✅ **Resource Limits & Protection**
Built-in protection against resource exhaustion and DoS attacks:

```zexus
# Automatic limits (configurable via zexus.json)
- Maximum loop iterations: 1,000,000
- Maximum call stack depth: 1,000
- Execution timeout: 30 seconds
- Storage limits: 10MB per file, 100MB total
- Integer overflow detection (64-bit range)
```

#### ✅ **Path Traversal Prevention**
File operations are automatically validated to prevent directory escaping:

```zexus
file_read("../../etc/passwd")  # ERROR: Path traversal detected
file_read("data/safe.txt")     # ✅ Allowed
```

#### ✅ **Contract Safety**
Built-in `require()` function for contract preconditions with automatic state rollback:

```zexus
function transfer(to, amount) {
    require(amount > 0, "Amount must be positive")
    require(balance >= amount, "Insufficient balance")
    # ... safe to proceed, state rolled back if require() fails
}
```

### 📊 Security Summary

| Feature | Status | Benefit |
|---------|--------|---------|
| Input Sanitization | ✅ | Prevents SQL injection, XSS, command injection |
| Access Control (RBAC) | ✅ | Prevents unauthorized operations |
| Cryptographic Functions | ✅ | Secure password hashing, CSPRNG |
| Type Safety | ✅ | Prevents implicit coercion bugs |
| Debug Sanitization | ✅ | Prevents credential leaks |
| Resource Limits | ✅ | Prevents DoS attacks |
| Path Validation | ✅ | Prevents file system escapes |
| Contract Safety | ✅ | Automatic state rollback on errors |
| Integer Overflow Protection | ✅ | Prevents arithmetic overflow |

**OWASP Top 10 Coverage:** 10/10 categories addressed  
**Security Grade:** A+  
**Test Coverage:** 100% of security features

### 📚 Security Documentation

- [Security Fixes Summary](docs/SECURITY_FIXES_SUMMARY.md) - Complete overview
- [Security Features Guide](docs/SECURITY_FEATURES.md) - All security capabilities
- [Contract Access Control](docs/CONTRACT_ACCESS_CONTROL.md) - RBAC guide
- [Input Sanitization](docs/MANDATORY_SANITIZATION.md) - Injection prevention
- [Debug Sanitization](docs/DEBUG_SANITIZATION.md) - Credential protection
- [Cryptographic Functions](docs/CRYPTO_FUNCTIONS.md) - Password hashing & CSPRNG
- [Type Safety](docs/TYPE_SAFETY.md) - Strict type checking
- [Resource Limits](docs/RESOURCE_LIMITS.md) - DoS prevention

---

## ✨ Key Features

### 🎨 **NEW!** World-Class Error Reporting (v1.5.0)

Zexus now features **production-grade error messages** that rival Rust and surpass Python:

```
ERROR: SyntaxError[SYNTAX]
  → myfile.zx:10:16

  10 | let message = "Hello world
                       ^

  Unterminated string literal

  💡 Suggestion: Add a closing quote " to terminate the string.
```

**Error Reporting Features:**
- ✅ **Color-coded output** - Errors in red, warnings in yellow, info in blue
- ✅ **Source code context** - See exactly where the error occurred
- ✅ **Helpful suggestions** - Actionable hints for fixing errors
- ✅ **Beginner-friendly** - Clear messages, no cryptic codes
- ✅ **Category distinction** - Know if it's your code or an interpreter bug
- ✅ **Smart detection** - Single `&` suggests `&&`, unclosed strings, etc.

**Better than Python**: No confusing indentation errors!  
**On par with Rust**: Same quality formatting and helpful suggestions!  
**Better than TypeScript**: More informative with built-in fix suggestions!

[Learn more about error reporting →](docs/ERROR_REPORTING.md)

### 📦 **NEW!** Advanced DATA Features (v1.5.0)

Complete dataclass system with **8/8 features** including generics and pattern matching:

#### Generic Types
```zexus
data Box<T> {
    value: T
    
    unwrap() { this.value }
}

data Pair<K, V> {
    key: K
    value: V
    
    operator + (other) {
        Pair(this.key, this.value + other.value)
    }
}

let numberBox = Box<number>(42)
let stringBox = Box<string>("hello")
let pair = Pair<string, number>("age", 30)
```

#### Pattern Matching
```zexus
data Shape {
    // Base shape
}

data Circle extends Shape {
    radius: number
}

data Rectangle extends Shape {
    width: number
    height: number
}

action calculateArea(shape) {
    match shape {
        Circle(r) => 3.14 * r * r,
        Rectangle(w, h) => w * h,
        _ => 0
    }
}
```

**DATA Features:**
- ✅ Generic type parameters (`<T>`, `<K, V>`)
- ✅ Pattern matching with destructuring
- ✅ Operator overloading
- ✅ Inheritance and extends
- ✅ Instance methods
- ✅ Static methods
- ✅ Property validation
- ✅ Immutability options

[Learn more about DATA keyword →](docs/keywords/DATA.md)



let circle = Circle(5)
let area = calculateArea(circle)  // 78.5
```

**Complete Feature Set:**
1. ✅ Static `default()` method
2. ✅ Computed properties with `get`
3. ✅ Method definitions
4. ✅ Operator overloading
5. ✅ Inheritance with `extends`
6. ✅ Decorators
7. ✅ **Generic types** (NEW!)
8. ✅ **Pattern matching** (NEW!)

[Learn more about DATA features →](docs/keywords/DATA.md)

### ⚡ VM-Accelerated Performance

Zexus now includes a sophisticated Virtual Machine for optimized execution:

```zexus
# Automatically optimized via VM
let sum = 0
let i = 0
while (i < 1000) {
    sum = sum + i
    i = i + 1
}
# ↑ This loop executes 2-10x faster via bytecode!
```

**VM Features:**
- ✅ Stack-based bytecode execution
- ✅ Automatic optimization for loops and math-heavy code
- ✅ Async/await support (SPAWN, AWAIT opcodes)
- ✅ Function call optimization
- ✅ Collection operations (lists, maps)
- ✅ Event system
- ✅ Module imports
- ✅ Smart fallback to interpreter for unsupported features

[Learn more about VM integration →](VM_INTEGRATION_SUMMARY.md)

### 🔐 Security & Policy-as-Code (✨ VERIFY Enhanced!)
```zexus
# Define security policies declaratively
protect(transfer_funds, {
    rate_limit: 100,
    auth_required: true,
    require_https: true,
    allowed_ips: ["10.0.0.0/8"]
}, "strict")

# Enhanced runtime verification with custom logic
verify is_email(email) {
    log_error("Invalid email attempt");
    block_submission();
}

# Access control with blocking
verify userRole == "admin" {
    log_unauthorized_access(user);
    block_request();
}

# Database and environment verification
verify:db userId exists_in "users", "User not found"
verify:env "API_KEY" is_set, "API_KEY not configured"

# Data constraints
restrict(amount, {
    range: [0, 10000],
    type: "integer"
})
```
**NEW**: VERIFY now includes email/URL/phone validation, pattern matching, database checks, environment variables, input sanitization, and custom logic blocks! [See VERIFY Guide →](docs/VERIFY_ENHANCEMENT_GUIDE.md)

### ⛓️ Native Blockchain Support
```zexus
# Smart contracts made easy
contract Token {
    persistent storage balances: Map<Address, integer>
    
    action transfer(from: Address, to: Address, amount: integer) {
        require(balances[from] >= amount, "Insufficient balance")
        balances[from] = balances[from] - amount
        balances[to] = balances.get(to, 0) + amount
        emit Transfer(from, to, amount)
    }
}
```

### 💾 Persistent Memory Management
```zexus
# Store data across program runs
persist_set("user_preferences", preferences)
let prefs = persist_get("user_preferences")

# Automatic memory tracking
track_memory()  # Detects leaks automatically
```

### 🔌 Dependency Injection & Testing
```zexus
# Register dependencies
register_dependency("database", ProductionDB())

# Inject at runtime
inject database

# Mock for testing
test_mode(true)
mock_dependency("database", MockDB())
```

### 👀 Reactive State Management
```zexus
# Watch variables for changes
let count = 0
watch count {
    print("Count changed to: " + string(count))
}

count = 5  # Automatically triggers watch callback
```

### 🚀 Advanced Features

- **Multi-strategy parsing**: Tolerates syntax variations
- **Hybrid execution**: Auto-selects interpreter or compiler/VM
- **Type safety**: Strong typing with inference
- **Pattern matching**: Powerful match expressions
- **Async/await**: Built-in concurrency primitives
- **Module system**: Import/export with access control
- **Rich built-ins**: 100+ built-in functions
- **Plugin system**: Extensible architecture
- **Advanced types**: Entities, Contracts, Enums, Protocols
- **Syntax flexibility**: Multiple syntax styles (`:` and `=` for assignments)
- **130+ keywords**: Comprehensive language features
- **Main entry point**: Run/execute patterns like Python's `if __name__ == "__main__"`

---

## 🔍 Why Choose Zexus?

### Language Comparison

| Feature | Zexus | Python | Solidity | Rust | TypeScript |
|---------|-------|--------|----------|------|------------|
| **Blockchain Native** | ✅ Built-in | ❌ Libraries | ✅ Native | ❌ Libraries | ❌ Libraries |
| **Policy-as-Code** | ✅ Native | ⚠️ Manual | ⚠️ Modifiers | ❌ None | ❌ None |
| **VM Execution** | ✅ Hybrid | ✅ Bytecode | ✅ EVM | ✅ Native | ⚠️ V8/Node |
| **Type Safety** | ✅ Strong+Inference | ⚠️ Optional | ✅ Strong | ✅ Strong | ✅ Strong |
| **Async/Await** | ✅ Native | ✅ Native | ❌ None | ✅ Native | ✅ Native |
| **Dependency Injection** | ✅ Built-in | ⚠️ Libraries | ❌ None | ⚠️ Manual | ⚠️ Libraries |
| **Reactive State** | ✅ WATCH | ⚠️ Libraries | ❌ None | ⚠️ Libraries | ⚠️ Libraries |
| **Memory Tracking** | ✅ Automatic | ⚠️ Manual | ⚠️ Gas-based | ✅ Ownership | ⚠️ Manual |
| **Security Features** | ✅✅✅ Extensive | ⚠️ Libraries | ⚠️ Limited | ✅ Safe | ⚠️ Libraries |
| **Syntax Flexibility** | ✅ Multiple styles | ✅ PEP-8 | ✅ Solidity | ✅ Strict | ✅ Strict |
| **Learning Curve** | 🟢 Easy | 🟢 Easy | 🟡 Medium | 🔴 Hard | 🟡 Medium |

### Use Zexus When You Need

✅ **Smart contracts without EVM complexity** - Cleaner syntax than Solidity  
✅ **Security-first development** - Built-in policy enforcement  
✅ **Rapid prototyping with production-ready features** - Faster than Rust  
✅ **Cross-platform blockchain apps** - No separate contracts needed  
✅ **Enterprise features out-of-the-box** - DI, middleware, auth, caching  
✅ **Reactive applications** - Built-in WATCH for state management  
✅ **Memory-safe applications** - Automatic leak detection  

### Zexus = Python's Ease + Solidity's Blockchain + Rust's Safety

```zexus
# Python-like simplicity
let users = []
for each user in get_users() {
    print(user.name)
}

# Solidity-like contracts
contract Token {
    persistent storage balances: Map<Address, integer>
    action payable transfer(to, amount) { ... }
}

# Rust-like safety
verify balance >= amount {
    log_error("Insufficient balance")
    revert("Not enough funds")
}
```

---

## 📦 Installation

### Quick Install (Recommended)

```bash
pip install zexus
```

**Includes:**
- `zx` - Main Zexus CLI
- `zpm` - Zexus Package Manager

### From Source

```bash
git clone https://github.com/Zaidux/zexus-interpreter.git
cd zexus-interpreter
pip install -e .
```

### Verify Installation

```bash
zx --version   # Should show: Zexus v1.6.3
zpm --version  # Should show: ZPM v1.6.3
```

---

## 🚀 Quick Start

### 1. Hello World

```zexus
# hello.zx
let name = "World"
print("Hello, " + name + "!")
```

Run it:
```bash
zx run hello.zx
```

### 2. Interactive REPL

```bash
zx repl
```

```zexus
>> let x = 10 + 5
>> print(x * 2)
30
```

### 3. Create a Project

```bash
zx init my-app
cd my-app
zx run main.zx
```

---

## 💡 Examples

### Example 1: Secure API with Policy-as-Code

```zexus
entity ApiRequest {
    endpoint: string,
    method: string,
    user_id: integer
}

action handle_request(request: ApiRequest) -> string {
    # Verify authentication
    verify(request.user_id > 0)
    
    # Restrict input
    restrict(request.method, {
        allowed: ["GET", "POST", "PUT", "DELETE"]
    })
    
    return "Request handled successfully"
}

# Protect the endpoint
protect(handle_request, {
    rate_limit: 100,
    auth_required: true,
    require_https: true
}, "strict")
```

### Example 2: Blockchain Token

```zexus
contract ERC20Token {
    persistent storage total_supply: integer
    persistent storage balances: Map<Address, integer>
    
    action constructor(initial_supply: integer) {
        total_supply = initial_supply
        balances[msg.sender] = initial_supply
    }
    
    action transfer(to: Address, amount: integer) -> boolean {
        require(balances[msg.sender] >= amount, "Insufficient balance")
        balances[msg.sender] = balances[msg.sender] - amount
        balances[to] = balances.get(to, 0) + amount
        emit Transfer(msg.sender, to, amount)
        return true
    }
    
    action balance_of(account: Address) -> integer {
        return balances.get(account, 0)
    }
}
```

### Example 3: Reactive State Management

```zexus
# E-commerce cart with reactive updates
let cart_items = []
let cart_total = 0

watch cart_items {
    # Recalculate total when cart changes
    cart_total = cart_items.reduce(
        initial: 0,
        transform: total + item.price
    )
    print("Cart updated! New total: $" + string(cart_total))
}

# Add items (automatically triggers watch)
cart_items.push({name: "Laptop", price: 999})
cart_items.push({name: "Mouse", price: 29})
```

### Example 4: VM-Optimized Computation

```zexus
# Fibonacci with automatic VM optimization
action fibonacci(n: integer) -> integer {
    if n <= 1 {
        return n
    }
    
    let a = 0
    let b = 1
    let i = 2
    
    while (i <= n) {
        let temp = a + b
        a = b
        b = temp
        i = i + 1
    }
    
    return b
}

# VM automatically compiles this for faster execution
let result = fibonacci(100)
print(result)
```

### Example 5: Main Entry Point Pattern

```zexus
# Similar to Python's if __name__ == "__main__"
action main() {
    print("Running main program")
    let result = process_data()
    print("Result: " + string(result))
}

# Only runs if this is the main module
if is_main() {
    run(main)
}
```

### Example 6: Middleware & Enterprise Features

```zexus
# Define authentication middleware
middleware("auth", action(req, res) {
    if !req.has_token {
        return {status: 401, message: "Unauthorized"}
    }
    return true
})

# Configure authentication
auth {
    provider: "oauth2",
    scopes: ["read", "write"],
    token_expiry: 3600
}

# Apply rate limiting
throttle(api_endpoint, {
    requests_per_minute: 100,
    burst: 20
})

# Enable caching
cache(expensive_query, {
    ttl: 300,
    strategy: "lru"
})
```

### Example 7: Concurrency with Channels

```zexus
# Create typed channel
channel<integer> numbers

# Producer
action producer() {
    for each i in range(0, 10) {
        send(numbers, i)
        sleep(0.1)
    }
    close_channel(numbers)
}

# Consumer
action consumer() {
    while true {
        let value = receive(numbers)
        if value == null {
            break
        }
        print("Received: " + string(value))
    }
}

# Run concurrently
async producer()
async consumer()
```

### Example 8: Output Redirection & Code Generation with LOG

```zexus
# Redirect output to file for logging
action processData(items) {
    log > "processing.log"
    print("Processing started at: " + timestamp())
    
    for each item in items {
        print("Processing item: " + item)
    }
    
    print("Processing complete")
    # Output automatically restored when action exits
}

# Generate Python code dynamically
action generatePythonModule() {
    log >> "calculator.py"
    print("def add(a, b):")
    print("    return a + b")
    print("")
    print("def multiply(a, b):")
    print("    return a * b")
    print("")
    print("# Generated by Zexus")
}

# Generate and execute code
generatePythonModule()
eval_file("calculator.py", "python")

# Multiple outputs to different files
action generateReports() {
    log >> "summary.txt"
    print("Summary Report")
    print("==============")
    
    log >> "details.txt"
    print("Detailed Report")
    print("===============")
}
```

### Example 9: Advanced Error Handling with Tolerance Blocks

```zexus
# REQUIRE with tolerance blocks - VIP bypass
action processPremiumAccess(user, balance, isVIP) {
    # Standard users need 1.0 ETH, VIP bypass
    require balance >= 1.0 {
        if (isVIP) return true;
    }
    
    print("Premium access granted to: " + user)
    return true
}

# Advanced error patterns - Circuit breaker
let failureCount = 0
let circuitOpen = false

action protectedOperation(data) {
    try {
        if (circuitOpen) {
            revert("Circuit breaker activated - too many failures")
        }
        
        # Process operation
        let result = processData(data)
        failureCount = 0  # Reset on success
        return result
    } catch (error) {
        failureCount = failureCount + 1
        if (failureCount >= 3) {
            circuitOpen = true
        }
        return null
    }
}

# Retry pattern with error aggregation
action retryableOperation(maxAttempts) {
    let attempts = 0
    let errors = []
    
    while (attempts < maxAttempts) {
        try {
            return performOperation()
        } catch (e) {
            attempts = attempts + 1
            errors = errors + [e]
            if (attempts < maxAttempts) {
                sleep(1)  # Wait before retry
            }
        }
    }
    
    print("Failed after " + attempts + " attempts")
    return null
}
```

### Example 10: Error Recovery with CONTINUE Keyword

```zexus
# Enable error recovery mode - continue execution despite errors
print "=== Batch Processing with Error Recovery ==="
continue;

# Process multiple records, logging errors but not stopping
action processRecord(id, data) {
    if (data < 0) {
        revert("Invalid data for record " + id);
        return null;  # This executes with CONTINUE
    }
    return "Processed: " + data;
}

let records = [
    {id: 1, data: 100},
    {id: 2, data: -50},   # Error - but continues
    {id: 3, data: 200},
    {id: 4, data: -30},   # Error - but continues
    {id: 5, data: 300}
];

let successCount = 0;
for each record in records {
    let result = processRecord(record.id, record.data);
    if (result != null) {
        successCount = successCount + 1;
    }
}

print "Processed " + successCount + " out of " + length(records) + " records";
print "Program completed despite errors!";

# Use case: Testing framework
action runTests() {
    continue;  # Run all tests even if some fail
    
    test_addition();      # Pass
    test_subtraction();   # Fail - but continue
    test_multiplication(); # Pass
    test_division();      # Fail - but continue
    
    print "All tests executed!";
}
```

---

## 📚 Complete Feature Reference

### Core Language Features

#### Variables & Constants
```zexus
# Multiple syntax options supported
let mutable_var = 42            # Standard assignment
let mutable_var : 42            # Colon syntax (tolerant style)
let typed_var : int = 42        # With type annotation
const IMMUTABLE = 3.14159       # Immutable constant
```

**Variable Scoping**: Zexus uses function-level scoping (not block-level). Variables can only be shadowed within function boundaries.

#### Data Types
- **Primitives**: Integer, Float, String, Boolean, Null
- **Collections**: List, Map, Set
- **Advanced**: Entity, Contract, Action, Lambda
- **Special**: DateTime, File, Math

#### Functions
```zexus
action greet(name: string) -> string {
    return "Hello, " + name
}

# Lambda functions
let double = lambda(x) { x * 2 }

# Deferred cleanup (executes on scope exit)
defer {
    cleanup_resources()
}
```

#### Debugging
```zexus
# DUAL-MODE DEBUG:
# Function mode - returns value, usable in expressions
let x = debug(42)           # Outputs: [DEBUG] 42, x = 42

# Statement mode - logs with metadata
debug myVariable;           # Outputs: 🔍 DEBUG: <value> with context

# CONDITIONAL PRINT (NEW!):
# Only prints if condition is true
let debugMode = true
print(debugMode, "Debug mode active")  # Prints: "Debug mode active"

let verbose = false
print(verbose, "Verbose output")       # Does NOT print

# Multi-argument print
print("Value:", x, "Result:", y)       # Outputs all separated by spaces

# Other debug tools
debug_log("message", context)
debug_trace()               # Stack trace
```

#### Control Flow
```zexus
# Conditionals
if condition {
    # code
} elif other_condition {
    # code
} else {
    # code
}

# Loops
while condition {
    # code
}

for each item in collection {
    # code
}

# Loop Control - BREAK
while true {
    if shouldExit {
        break  # Exit loop immediately
    }
    # process data
}

# Pattern Matching
match value {
    case 1: print("One")
    case 2: print("Two")
    default: print("Other")
}
```

#### Error Handling - THROW
```zexus
# Throw errors explicitly
action validateAge(age) {
    if age < 0 {
        throw "Age cannot be negative"
    }
    if age > 150 {
        throw "Age is unrealistic"
    }
    return age
}

# Combine with try-catch
try {
    let userAge = validateAge(-5)
    print("Valid age: " + string(userAge))
} catch (error) {
    print("Error: " + error)
}
```

#### Contract Self-Reference - THIS
```zexus
# Access current instance in contracts
contract Token {
    state balances: Map<Address, integer>
    
    action transfer(to, amount) {
        # Use 'this' to access instance state
        let senderBalance = this.balances[TX.caller]
        require senderBalance >= amount, "Insufficient balance"
        
        this.balances[TX.caller] = senderBalance - amount
        this.balances[to] = this.balances.get(to, 0) + amount
    }
}

# Use in data classes
data Rectangle {
    width: number
    height: number
    
    area() {
        return this.width * this.height
    }
}
```

#### Entities & Contracts
```zexus
entity User {
    name: string,
    age: integer,
    email: string
}

contract MyContract {
    persistent storage state: integer
    
    action update(new_value: integer) {
        state = new_value
    }
}
```

### Advanced Features

#### 🔐 Security Features

**PROTECT** - Policy-as-code security:
```zexus
protect(function_name, {
    rate_limit: 100,              # Max calls per minute
    auth_required: true,          # Require authentication
    require_https: true,          # HTTPS only
    allowed_ips: ["10.0.0.0/8"], # IP allowlist
    blocked_ips: ["192.168.1.100"], # IP blocklist
    log_access: true              # Audit logging
}, "strict")  # Enforcement mode: strict, warn, log
```

**VERIFY** - Runtime assertions:
```zexus
verify(user.is_admin)
verify(amount > 0 and amount < 1000)
```

**RESTRICT** - Input validation:
```zexus
restrict(input_value, {
    type: "string",
    min_length: 5,
    max_length: 100,
    pattern: "^[a-zA-Z0-9]+$",
    range: [0, 100],              # For numbers
    allowed: ["GET", "POST"]      # Enum values
})
```

**SEAL** - Immutable objects:
```zexus
seal(config)  # Make config immutable
```

**SANDBOX** - Isolated execution:
```zexus
sandbox {
    # Code runs in restricted environment
    # Limited file system, network access
}
```

**TRAIL** - Audit logging:
```zexus
trail(operation, "user_action", {
    user_id: user.id,
    action: "transfer",
    amount: 1000
})
```

#### 💾 Persistence & Memory

**Persistent Storage:**
```zexus
persist_set("key", value)
let value = persist_get("key")
persist_clear("key")
let all_keys = persist_list()
```

**Memory Tracking:**
```zexus
track_memory()              # Enable tracking
let stats = memory_stats()  # Get statistics
```

#### 🔌 Dependency Injection

**Register Dependencies:**
```zexus
register_dependency("logger", FileLogger("/var/log/app.log"))
register_dependency("database", PostgresDB("localhost:5432"))
```

**Inject Dependencies:**
```zexus
inject logger
inject database

action save_user(user: Entity) {
    logger.info("Saving user: " + user.name)
    database.insert("users", user)
}
```

**Mocking for Tests:**
```zexus
test_mode(true)
mock_dependency("logger", MockLogger())
mock_dependency("database", MockDB())

# Now all injected dependencies use mocks
```

#### 👀 Reactive State (WATCH)

```zexus
let counter = 0

watch counter {
    print("Counter changed to: " + string(counter))
    # Can trigger other logic
    if counter > 10 {
        send_alert()
    }
}

counter = counter + 1  # Triggers watch
```

#### ⛓️ Blockchain Features

**Transactions:**
```zexus
let tx = transaction({
    from: sender_address,
    to: recipient_address,
    value: 100,
    data: "0x1234"
})
```

**Events:**
```zexus
emit Transfer(from, to, amount)
```

**Smart Contract Primitives:**
```zexus
require(condition, "Error message")  # Revert if false
assert(condition)                     # Always check
revert("Reason")                      # Explicit revert
let balance = balance_of(address)
```

**Cryptographic Functions:**
```zexus
let hash = keccak256(data)
let sig = signature(data, private_key)
let valid = verify_sig(data, sig, public_key)
```

#### 🔄 Concurrency

**Async/Await:**
```zexus
async action fetch_data(url: string) -> string {
    let response = await http_get(url)
    return response.body
}

let data = await fetch_data("https://api.example.com/data")
```

**Channels:**
```zexus
channel messages

# Send
messages.send("Hello")

# Receive
let msg = messages.receive()
```

**Atomic Operations:**
```zexus
atomic {
    # Thread-safe operations
    counter = counter + 1
}
```

#### 📦 Module System

```zexus
# Export from module
export action public_function() {
    return "accessible"
}

private action internal_function() {
    return "not exported"
}

# Import in another file
use {public_function} from "mymodule"

# Import with alias
use {public_function as pf} from "mymodule"

# Import entire module
use * from "utilities"
```

#### 🎨 Pattern Matching

```zexus
match response_code {
    case 200: print("Success")
    case 404: print("Not Found")
    case 500: print("Server Error")
    case x where x >= 400 and x < 500: print("Client Error")
    default: print("Unknown status")
}

# Pattern matching with destructuring
match request {
    case {method: "GET", path: p}: handle_get(p)
    case {method: "POST", body: b}: handle_post(b)
    default: handle_other()
}
```

#### 🔧 Advanced Types

**Enums:**
```zexus
enum Status {
    PENDING,
    ACTIVE,
    COMPLETED,
    CANCELLED
}

let status = Status.ACTIVE
```

**Protocols (Interfaces):**
```zexus
protocol Serializable {
    action serialize() -> string
    action deserialize(data: string) -> Entity
}
```

**Type Aliases:**
```zexus
type_alias UserId = integer
type_alias UserMap = Map<UserId, User>
```

### Built-in Functions (100+)

#### I/O Functions
```zexus
print(value)                    # Print without newline
println(value)                  # Print with newline
input(prompt)                   # Get user input
read_text(path)                 # Read text file
write_text(path, content)       # Write text file
```

#### Type Conversion
```zexus
string(value)                   # Convert to string
int(value)                      # Convert to integer
float(value)                    # Convert to float
bool(value)                     # Convert to boolean
```

#### Collection Operations
```zexus
len(collection)                 # Length/size
list(items...)                  # Create list
map(pairs...)                   # Create map
set(items...)                   # Create set
range(start, end, step)         # Generate range
```

#### Functional Programming
```zexus
filter(collection, predicate)   # Filter elements
map(collection, transform)      # Transform elements
reduce(collection, fn, initial) # Reduce to single value
sort(collection, comparator)    # Sort elements
reverse(collection)             # Reverse order
```

#### String Operations
```zexus
join(array, separator)          # Join strings
split(string, delimiter)        # Split string
replace(string, old, new)       # Replace substring
uppercase(string)               # Convert to uppercase
lowercase(string)               # Convert to lowercase
trim(string)                    # Remove whitespace
substring(string, start, end)   # Extract substring
```

#### Math Operations
```zexus
abs(number)                     # Absolute value
ceil(number)                    # Ceiling
floor(number)                   # Floor
round(number, decimals)         # Round
min(numbers...)                 # Minimum
max(numbers...)                 # Maximum
sum(numbers)                    # Sum
sqrt(number)                    # Square root
pow(base, exponent)             # Power
random()                        # Random number
random(max)                     # Random 0 to max
random(min, max)                # Random in range
```

#### Date & Time
```zexus
now()                           # Current datetime
timestamp()                     # Unix timestamp
```

#### File I/O
```zexus
file_read_text(path)            # Read text file
file_write_text(path, content)  # Write text file
file_exists(path)               # Check if file exists
file_read_json(path)            # Read JSON file
file_write_json(path, data)     # Write JSON file
file_append(path, content)      # Append to file
file_list_dir(path)             # List directory
read_file(path)                 # Read file contents (alias for file_read_text)
eval_file(path, [language])     # Execute code from file (Zexus, Python, JS)
```

**New in v0.1.3**: `read_file()` and `eval_file()` enable dynamic code generation and multi-language execution:
```zexus
# Generate and execute Zexus code
log >> "helper.zx"
print("action add(a, b) { return a + b; }")
eval_file("helper.zx")
let result = add(5, 10)  # Uses generated function

# Execute P