code: func Map(f func(float64) float64, xs []float64) []float64 {
  	// TODO(austin) Parallelize
  	res := make([]float64, len(xs))
  	for i, x := range xs {
  		res[i] = f(x)
  	}
  	return res
  }
docs: // Map returns f(x) for each x in xs.
  //
  // f may be evaluated in parallel and in any order.