Olin – Defining a new operating primitive for event-driven services(christine.website)

    handle = ask_user_for_media_input()
    wire_up_graph(handle)
    if(supported(handle, "dvd player")) {
        enable_eject_button();
    }

    #include <os.h>                             // Invoke(handle, char *interface, void *in, void *out) -> bool
                                                // Close(handle) -> void
    #include <os/interface.h>                   // GetInterface(handle, char *interface) -> void *
                                                // Require(handle, char *interface) -> void *
    #include <os/services/console.h>            // IF_CONSOLE, Console, Console_write
    #include <os/services/filesystem.h>         // IF_FILESYSTEM, Filesystem, Filesystem_open, Filesystem_error
    #include <os/services/stream.h>             // IF_STREAM, Stream_read, Stream_write
    #include <os/services/buffered_stream.h>    // IF_BUFFERED_STREAM, BufferedStream_sync

    int main(void)
    {
        Filesystem fs = Require(NULL, IF_FILESYSTEM);
        Console console = Require(NULL, IF_CONSOLE);

        File *fp;
        if((fp = Filesystem_open(fs, "/etc/passwd", O_RDWR)) == NULL) {
            Console_write(console, "open failed: %s", Filesystem_error(fs));
            return 1;
        }

        if(File_write(fp, "foo\n") == -1) {
            Console_write(console, "write failed: %s", Filesystem_error(fs));
            return 1;
        }

        // Optional. Underlying Invoke() will fail if interface absent.
        BufferedStream_sync((BufferedStream) fp);

        return 0;
    }