// type of i is int
	// type of s is string
	// s == a[i]
	g(i, s)
}

var key string
var val interface{}  // element type of m is assignable to val
m := map[string]int{"mon":0, "tue":1, "wed":2, "thu":3, "fri":4, "sat":5, "sun":6}
for key, val = range m {
	h(key, val)
}
// key == last map key encountered in iteration
// val == map[key]

var ch chan Work = producer()

    *   Add `tf.contrib.data.prefetch_to_device`, which enables prefetching
        dataset elements to GPU memory.
    *   Add `tf.contrib.data.AUTOTUNE`, which allows the tf.data runtime to
        automatically tune the prefetch buffer sizes based on your system and
        environment.
    *   Add `tf.contrib.data.make_csv_dataset` for building datasets of CSV
        files.
*   Eager Execution: