RPN-calculator-js

The RPN calculator implementation is a good exercise for working through a languages capabilities and exploring OO strategies.

I have done four variations of the RPN calculator as exploratory into languages:

• java
• scala
• javascript / node.js
• python

How to run

This implementation utilizes node.js and mocha.

Prereqs

To install node.js, either download or install using brew

brew install node

To install the node modules:

npm install

Run from command line

You can run the calculator from the command line by running:

node calculator-commandline.js 1 2 +

Note that '*' has unix command line meaning, so us 'x' or '\*' for multiplication.

>node calculator-commandline.js 3 2 \*
result: 6
>node calculator-commandline.js 3 2 x
result: 6

Unit Test

To run the unit tests, run the following shell script:

npm test

To add a new operator

1. Create a new operator implementation class. Add this class to the operators directory. Follow the conventation of (operator name)-operator.js (example: addition-operator.js).

2. The operator implementation class needs to implement a function function(numbers), where numbers is an instance of RPN-stack. The function is responsible for pop-ing the operands necessary to perform the operation, and push-ing the result back to the stack. Either export this as module.exports.doOperation or module.exports

A sample base implementation for addition is shown below:

module.exports = function(numbers) {
	var rhs = numbers.pop();
	var lhs = numbers.pop();
	var result = lhs + rhs;
	numbers.push(result);
	return result;
};

3. Register operator in operator-register.js. To do this, add the following statement:

registry.registerHandler("+", require("./operators/addition-operator"));