Return early and continue on the other path

A guard clause handles a special case before the main computation:

def clamp_low(value: i64, minimum: i64) -> i64:
    if value < minimum:
        return minimum
    value

def main() -> Result[(), IoError]:
    print(clamp_low(3, 10))?
    print(clamp_low(12, 10))?
    Ok(())

10
12

return exits the entire function, even when it appears in nested branches. Every return must match the function’s declared result. Code after a guaranteed exit is rejected. Every path that reaches the end must also supply the declared result; handling just one branch is not enough:

def incomplete(flag: bool) -> i64:
    if flag:
        return 42

def main() -> ():
    pass

expected i64, got ()