The Calculator example demonstrates how simple it is to write a calculator
with parserlib.

When the program runs, you can enter an expression that contains:

-floating point numbers.
-addition, subtraction, multiplication and division.
-parentheses.

For example:

    1 + (2 * 3)
    3.14 / 7.1
    
Press enter to exit the application, when requested to input an expression.

The Calculator example contains a left-recursive grammar.