if promopt then async

src/main.rs

@@ -30,6 +30,7 @@ fn play_with_flags(flags: &flags::Flags) {
     ));
 
     let mut i = 0;
+    let mut sync = true;
     for p in flags.play.iter() {
         for p in play::new(p.clone()) {
             syn_seq.append(i as i32, p);
@@ -37,11 +38,12 @@ fn play_with_flags(flags: &flags::Flags) {
         }
     }
     if i == 0 {
+        sync = false;
         let s: String = prompt!("> ").parse().expect("failed to readline");
         panic!("not impl");
     }
 
-    play(syn_seq, flags.sample_rate, flags.bpm, true);
+    play(syn_seq, flags.sample_rate, flags.bpm, sync);
 }
 
 fn play(mut s: seq::SynSeq, sample_rate: usize, bpm: usize, sync: bool) {