//ww:run-exit 80
// Migrated from 775_io_vtable_run row writer_set_happy.
package main;
import io;
fn mywrite(s: io.stream, buf: []u8) (size | io.error) = {
    return buf.len: size;
};
export fn main() i32 = {
    let vt: io.vtable;
    vt.writer = (&mywrite): *io.writer;
    let v: io.stream = &vt;
    let buf: [5]u8;
    let bs: []u8 = buf[0:5];
    let r = io.write(v, bs);
    if (r is size) {
        let n = r as size;
        if (n == 5: size) { return 80; };
        return 81;
    };
    return 99;
};