f("hello", "world") // f runs; we wait

go f("hello", "world") // f starts running
g() // does not wait for f to return

timerChan := make(chan time.Time)
go func() {
    time.Sleep(deltaT)
    timerChan <- time.Now() // send time on timerChan
}()
// Do something else; when ready, receive.
// Receive will block until timerChan delivers.
// Value sent is other goroutine's completion time.
completedAt := <-timerChan

select {
case v := <-ch1:
    fmt.Println("channel 1 sends", v)
case v := <-ch2:
    fmt.Println("channel 2 sends", v)
default: // optional
    fmt.Println("neither channel was ready")
}

func Query(conns []Conn, query string) Result {
    ch := make(chan Result, len(conns))  // buffered
    for _, conn := range conns {
        go func(c Conn) {
            ch <- c.DoQuery(query):
        }(conn)
    }
    return <-ch
}

func XQuery(conns []Conn, query string) Result {
    ch := make(chan Result, 1)  // buffer of 1 item
    for _, conn := range conns {
      go func(c Conn) {
        select {
          case ch <- c.DoQuery(query):
            // nothing to do
          default: // executes if ch is blocked
            // nothing to do
        }
      }(conn)
    }
    return <-ch
}


func Compose(f, g func(x float) float)
                  func(x float) float {
     return func(x float) float {
        return f(g(x))
    }
}

print(Compose(sin, cos)(0.5))

go func() { // copy input to output
	for val := range input {
		output <- val
	}
}()