code: func Range(start, end int) []int {
  	if end < start {
  		panic("range must have end greater than or equal to start")
  	}
  	r := make([]int, end-start)
  	for i := start; i < end; i++ {
  		r[i-start] = i
  	}
  	return r
  }
docs: // Range generates a list of integers corresponding to every integer in
  // the half-open interval [x, y).
  //
  // Range will panic if `end < start`.