code: func Register(distType Type, f newDistribution) {
  	if _, ok := distributions[distType]; ok {
  		panic(fmt.Errorf("distribution %q already registered", distType))
  	}
  	distributions[distType] = f
  }
docs: // Register registers a function that returns a new instance of the given
  // distribution. This is intended to be called from the init function in
  // packages that implement distribution functions.