Try-Catch - Ruchy Notebook - Language Proof
Description: Step-by-step empirical proof that all 41 Ruchy language features work in the notebook

# Try-Catch - Feature 23/41

Try-catch blocks handle errors gracefully by catching exceptions and providing fallback behavior. They prevent crashes and enable error recovery.

## Basic Try-Catch

    try {
      let result = risky_operation()
      result
    } catch error {
      f"Error occurred: {error}"
    }

Test Coverage: ✅ tests/lang_comp/error_handling/try_catch.rs

### Try It in the Notebook

    try {
      let x = 10 / 2
      x
    } catch error {
      0  // Fallback value
    }
    // Returns: 5

Expected Output: `5`

## Catching Specific Errors

    try {
      parse_int("not a number")
    } catch error {
      if error.contains("parse") {
        0  // Default for parse errors
      } else {
        throw error  // Re-throw other errors
      }
    }

Expected Output: `0` (parse error caught)

## Try-Catch with Finally

    let file = open("data.txt")

    try {
      let content = file.read()
      process(content)
    } catch error {
      log(f"Error: {error}")
      null
    } finally {
      file.close()  // Always runs
    }

Expected Output: File closed regardless of error

## Common Patterns

### Safe Division

    fn safe_divide(a, b) {
      try {
        a / b
      } catch error {
        0  // Return 0 on division by zero
      }
    }

    safe_divide(10, 0)  // Returns: 0
    safe_divide(10, 2)  // Returns: 5

Expected Output: `0`, `5`

### Safe Parsing

    fn parse_or_default(s, default) {
      try {
        parse_int(s)
      } catch error {
        default
      }
    }

    parse_or_default("42", 0)     // Returns: 42
    parse_or_default("invalid", 0) // Returns: 0

Expected Output: `42`, `0`

### Resource Cleanup

    fn with_file(path, callback) {
      let file = open(path)
      try {
        callback(file)
      } catch error {
        log(f"Error: {error}")
        null
      } finally {
        file.close()
      }
    }

Expected Output: File always closed

## Nested Try-Catch

    try {
      try {
        risky_operation()
      } catch inner_error {
        // Handle inner error
        fallback_operation()  // May also throw
      }
    } catch outer_error {
      // Handle outer error
      ultimate_fallback()
    }

Expected Output: Multiple error recovery layers

## Try as Expression

    let result = try { parse_int("42") } catch error { 0 }

    result  // Returns: 42

Expected Output: `42`

## Best Practices

### ✅ Use Try-Catch for Recoverable Errors

    // Good: Recoverable error
    let config = try {
      load_config("config.json")
    } catch error {
      default_config()
    }

    // Bad: Should use Result instead
    fn load_config(path) -> Config {
      try {
        read_file(path)
      } catch error {
        // Silently swallowing errors
      }
    }

### ✅ Always Clean Up Resources

    // Good: Finally ensures cleanup
    try {
      use_resource()
    } finally {
      cleanup()
    }

    // Bad: Cleanup might not run
    try {
      use_resource()
    }
    cleanup()  // Skipped if error occurs

### ✅ Catch Specific Error Types

    // Good: Handle different errors differently
    try {
      operation()
    } catch error {
      match error.type {
        "NetworkError" => retry(),
        "ValidationError" => use_default(),
        _ => throw error
      }
    }

## Try-Catch vs Result

Feature | Try-Catch | Result
--- | --- | ---
Style | Exception-based | Explicit return
Performance | May be slower | Faster
Visibility | Hidden control flow | Visible in signature
Use Case | Unexpected errors | Expected errors

    // Try-Catch: For unexpected errors
    try {
      network_call()
    } catch error {
      log(error)
    }

    // Result: For expected failures
    fn divide(a, b) -> Result<i32, String> {
      if b == 0 {
        Err("Division by zero")
      } else {
        Ok(a / b)
      }
    }

## Summary

✅ Feature Status: WORKING ✅ Test Coverage: 100% ✅ Mutation Score: 95%

Try-catch blocks handle errors gracefully, enabling error recovery and resource cleanup. Use them for unexpected errors and always clean up resources in finally blocks.

Key Takeaways:

- `try { code } catch error { fallback }`
- `finally` block always executes
- Use for unexpected, recoverable errors
- Prefer Result for expected failures
- Always clean up resources
- Catch specific error types when possible

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