Guarded Patterns (if conditions in match)

1Concept

A guard clause (`if boolean_condition`) can be appended to any case pattern. The case succeeds ONLY if both the pattern structure matches AND the guard expression evaluates to True.

2Architecture Diagram

case [x, y] if x == y: ---> Matches 2-element sequence where both elements are equal!

3Code Example

def categorize_number(val):
    match val:
        case int(n) if n > 0 and n % 2 == 0:
            return f"Positive Even Integer: {n}"
        case int(n) if n > 0:
            return f"Positive Odd Integer: {n}"
        case int(n) if n < 0:
            return f"Negative Integer: {n}"
        case _:
            return "Zero or Non-Integer"

print(categorize_number(42))
print(categorize_number(-15))

4Expected Output

Positive Even Integer: 42
Negative Integer: -15

5Key Takeaways

• ✓Variables bound in the pattern are accessible inside the `if` guard condition.
• ✓If the guard fails, matching continues to subsequent `case` branches.
• ✓Guards prevent deep nested if-checks inside pattern matching blocks.