Repeat until a condition changes

Use while when a condition determines how long to repeat. The condition must be bool, and it is checked before every iteration, including the first:

def main() -> Result[(), IoError | OverflowError[i64]]:
    mut remaining = 3
    while remaining > 0:
        print(remaining)?
        remaining = remaining - 1
    print("go")?
    Ok(())

3
2
1
go

continue skips the rest of the current iteration. break exits the loop:

def main() -> Result[(), IoError | OverflowError[i64] | ZeroDivisionError]:
    mut n = 0
    while True:
        n = n + 1
        if n % 2 == 0:
            continue
        if n > 5:
            break
        print(n)?
    Ok(())

1
3
5

Update the condition’s inputs before a continue when needed; otherwise a while loop can repeat forever. In a for loop, continue automatically advances to the next element:

def main() -> Result[(), IoError]:
    for n in range(6):
        if n == 1:
            continue
        if n == 4:
            break
        print(n)?
    Ok(())

0
2
3

break and continue affect only the innermost loop. Use return to leave the function. break cannot carry a value, and loop else clauses are not supported.

Even after while True, a function returning data still needs a result after the loop. Statements directly after an unconditional exit are rejected:

def main() -> Result[(), IoError]:
    while True:
        break
        print("unreachable")?
    Ok(())

unreachable statement after a control-flow exit