Counting down

# Counting down: the step is its own signed number, not a value the counter takes (2026-09-23).
# A position is a uint64, so walking a list backwards needs exactly this.
MAIN {
    for 'i': uint64 from 3 to 1 by -1 { std::print.useful['i', " "]; }
    std::print.stored[newln];
    for 'j': uint64 from 3 to 0 by -1 { std::print.useful['j', " "]; }   # ends at 0: must not underflow
    std::print.stored[newln];
    let 'xs' := [10, 20, 30];
    for 'k': uint64 from list.length[lend 'xs'] to 1 by -1 { std::print.useful['xs'[pos 'k'], " "]; }
    std::print.stored[newln];
}