code: public static VectorFunction asPlusFunction(final double arg) {
          return new VectorFunction() {
              @Override
              public double evaluate(int i, double value) {
                  return value + arg;
              }
          };
      }
docs: Creates a plus function that adds given {@code value} to it's argument.
  
  @param arg a value to be added to function's argument
  
  @return a closure object that does {@code _ + _}