Control Flow and Exceptions

@dataclass
class Break(Exception):
    target: str
    """
    Exception for implementing labeled break statements.
    
    Attributes:
    - target: str - The label name to break to
    """

@dataclass  
class Continue(Exception):
    target: str
    """
    Exception for implementing labeled continue statements.
    
    Attributes:
    - target: str - The label name to continue to
    """

class TailCall(Exception):
    """
    Exception for implementing tail call optimization.
    Used to implement tail recursive calls efficiently.
    """

@dataclass
class HaltException(Exception):
    message: str
    """
    Exception thrown when a Dafny program halts with an error.
    
    Attributes:
    - message: str - The halt message describing the error
    """

def label(name: str = None):
    """
    Context manager for handling labeled breaks and tail calls.
    
    Parameters:
    - name: str, optional - Label name for targeted breaks
    
    Usage:
    with label("outer_loop"):
        # code that may raise Break("outer_loop") or TailCall
        pass
    """

def c_label(name: str = None):
    """
    Context manager for handling labeled continues.
    
    Parameters:
    - name: str, optional - Label name for targeted continues
    
    Usage:
    with c_label("inner_loop"):
        # code that may raise Continue("inner_loop")
        pass
    """

from _dafny import Break, Continue, TailCall, HaltException

# Create control flow exceptions
break_exc = Break("outer_loop")
continue_exc = Continue("inner_loop")
halt_exc = HaltException("Division by zero")

# These would typically be raised within Dafny-generated code
# raise break_exc      # Would break to "outer_loop" label
# raise continue_exc   # Would continue at "inner_loop" label  
# raise halt_exc       # Would halt program with error message

from _dafny import Break, Continue, label, c_label

# Simulating nested loops with labeled break
try:
    with label("outer"):
        for i in range(10):
            with label("inner"):
                for j in range(10):
                    if i * j > 20:
                        raise Break("outer")  # Break out of both loops
                    if j == 5:
                        raise Break("inner")  # Break only inner loop
                    print(f"i={i}, j={j}")
except Break:
    pass  # Break was handled by appropriate label context

# Labeled continue example
try:
    with c_label("outer"):
        for i in range(5):
            with c_label("inner"):
                for j in range(5):
                    if j == 2:
                        raise Continue("inner")  # Continue inner loop
                    if i == 3:
                        raise Continue("outer")  # Continue outer loop
                    print(f"Processing i={i}, j={j}")
except Continue:
    pass  # Continue was handled by appropriate label context

from _dafny import TailCall, label

def factorial_helper(n, acc):
    """Tail-recursive factorial implementation."""
    if n <= 1:
        return acc
    else:
        # In Dafny, this would be a tail call
        # The TailCall exception enables optimization
        raise TailCall()  # Signal tail call optimization needed

def factorial(n):
    """Factorial with tail call optimization."""
    acc = 1
    while True:
        try:
            with label():  # Unnamed label catches TailCall
                if n <= 1:
                    return acc
                acc = acc * n
                n = n - 1
                raise TailCall()  # Tail call optimization
        except TailCall:
            continue  # Loop continues for tail call

from _dafny import HaltException

def safe_divide(a, b):
    """Division with Dafny-style halting on error."""
    if b == 0:
        raise HaltException("Division by zero is not allowed")
    return a / b

# Usage that might halt
try:
    result = safe_divide(10, 0)
except HaltException as e:
    print(f"Program halted: {e.message}")
    # In Dafny runtime, this would terminate the program

from _dafny import Break, Continue, HaltException, label, c_label

def complex_search(matrix, target):
    """
    Complex search with multiple control flow constructs.
    Demonstrates nested labels and different exception types.
    """
    try:
        with label("search_complete"):
            for row_idx in range(len(matrix)):
                with c_label("next_row"):
                    with label("row_complete"):
                        for col_idx in range(len(matrix[row_idx])):
                            with c_label("next_col"):
                                value = matrix[row_idx][col_idx]
                                
                                if value is None:
                                    raise HaltException("Null value encountered in matrix")
                                
                                if value == target:
                                    print(f"Found {target} at ({row_idx}, {col_idx})")
                                    raise Break("search_complete")
                                
                                if value < 0:
                                    print(f"Skipping negative value at ({row_idx}, {col_idx})")
                                    raise Continue("next_col")
                                
                                if value > 100:
                                    print(f"Large value at ({row_idx}, {col_idx}), skipping row")
                                    raise Continue("next_row")
                                
                                print(f"Checking ({row_idx}, {col_idx}): {value}")
                        
                        print(f"Completed row {row_idx}")
            
            print("Search completed - target not found")
                            
    except HaltException as e:
        print(f"Search halted: {e.message}")
        return None
    except (Break, Continue):
        # These should have been caught by their respective labels
        print("Uncaught control flow exception")
        return None

# Example usage
test_matrix = [
    [1, 2, 3, 4],
    [5, -1, 7, 8], 
    [9, 10, 50, 12]
]

complex_search(test_matrix, 50)  # Will find target
complex_search(test_matrix, 999) # Will complete search without finding