Reverse Polish Notation Calculator
==================================
The first example is that of a simple double-precision "reverse
polish notation" calculator (a calculator using postfix operators).
This example provides a good starting point, since operator precedence
is not an issue. The second example will illustrate how operator
precedence is handled.
The source code for this calculator is named `rpcalc.y'. The `.y'
extension is a convention used for Bison input files.