Io - polling for key down event - how to?

Hello all, I was wondering what an approach might be for polling a buffer for a key-down event? Would I use

I have a pause function…

  • Current tragic state:
    • read first byte of user input from \n terminated string (sigh)
    • q → exit program
    • otherwise → continue execution
  • Preferred awesome state:
    • poll key-down buffer for key-down event
    • ESC → exit program
    • other key down → continue execution
    • no input received → perform some other action (in my use case - animate ansi text fx), then return to polling

what might be an approach? I suppose a key-down buffer is optional at this point, could make the end-user hold key-down until key-down polling finds it…but would be nice if they don’t have to.

pub fn pause() void {
    //todo - poll / read a keystroke w/out echo, \n etc

    emit("Press return to continue...");
    var b: u8 = undefined;
    b = stdin.readByte() catch undefined;

    if (b == 'q') {
        //exit cleanly

GitHub Src

What is the catch undefined for? It seems to me like it should be catch unreachable if it is impossible to happen, otherwise it should be catch 0 or something that has guaranteed behavior in your control flow. I know undefined is typically 0’s or 0xA’s, but it could be anything, including ‘q’. Unless you literally mean, “I don’t care at all what the value is or what behavior we choose. YOLO”

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I’m trying to do something similar as well the best thing I found was they way the project zig-spoon by Leon Plickat does it in the demos for his library.

Something along the line of:

    // Open tty
    var tty = try std.fs.cwd().openFile("/dev/tty", .{ .mode = .read_write });
    // No idea
    var fds: [1]std.os.pollfd = undefined;
    // No idea 2
    fds[0] = .{
        .fd = tty.handle,
        .events = std.os.POLL.IN,
        .revents = undefined,
    // Buffer to holf the user input
    var buffer: [16]u8 = undefined;

    while (run) {
        _ = try std.os.poll(&fds, -1);
        _ = try, &buffer);


I think you should be able to do this with stdio instead of tty.

But I am a beginner and don’t fully understand that code honestly :smiling_face_with_tear: but maybe it helps you go in the right direction.