Add Tick to run timers independent of the system clock

subscriptions.go

@@ -9,9 +9,10 @@ import (
 type NewEveryMsg func(time.Time) Msg
 
 // Every is a subscription that ticks with the system clock at the given
-// duration.
+// duration, similar to cron. It's particularly useful if you have several
+// subscriptions that need to run in sync.
 //
-// TODO: make it cancelable
+// TODO: make it cancelable.
 func Every(duration time.Duration, newMsg NewEveryMsg) Sub {
 	return func() Msg {
 		n := time.Now()
@@ -23,3 +24,17 @@ func Every(duration time.Duration, newMsg NewEveryMsg) Sub {
 		}
 	}
 }
+
+// Tick is a subscription that at an interval independent of the system clock
+// at the given duration. That is, it begins precisely when invoked.
+//
+// TODO: make it cancelable.
+func Tick(d time.Duration, newMsg NewEveryMsg) Sub {
+	return func() Msg {
+		t := time.NewTimer(d)
+		select {
+		case now := <-t.C:
+			return newMsg(now)
+		}
+	}
+}