Creating generators

An ordinary function can create and return a generator:

def numbers() -> Generator[i64]:
    yield 10
    yield 20

def source() -> Generator[i64]:
    numbers()

def total() -> Result[i64, OverflowError[i64]]:
    values = source()
    mut result = 0
    for n in values:
        result = result + n
    Ok(result)

def main() -> Result[(), IoError | OverflowError[i64]]:
    print(total()?)?
    Ok(())

30

A factory that can fail can return Result[Generator[T], E]. Write Ok(numbers()) for success and use ? at the factory’s call site. Wrapping a generator adds no allocation; dropping the wrapper releases its captures without resuming the body.