code: public OperatorTable<T> prefix(
        Parser<? extends Function<? super T, ? extends T>> parser, int precedence) {
      ops.add(new Operator(parser, precedence, Associativity.PREFIX));
      return this;
    }
docs: Adds a prefix unary operator.
  
  @param parser the parser for the operator.
  @param precedence the precedence number.
  @return this.