pub fn main(world: World) -> Void raises {
    let input: Span<u8> = "alpha\nzero beta\nzero gamma\n"
    var start: usize = 0
    var matches: usize = 0
    while start < std.mem.len(input) {
        let line: Maybe<Span<u8>> = std.io.nextLine(input, start)
        if line.has && std.str.contains(line.value, "zero") {
            matches = matches + 1
        }
        start = std.io.nextLineStart(input, start)
    }
    if matches == 2 && std.io.countLines(input) == 3 {
        check world.out.write("grep scan ok\n")
    }
}