Infix Evaluator

This infix evaluator will correctly solve any expression given only numbers, operators (+, -, *, /), and groups ((), {}, []). The infix evaluator will tokenize the expression string, pass it to the evaluator and return the results.

Getting Started

Clone the repository
git clone git@github.com:apipkin/InfixEvaluator.git

Change into the directory
cd InfixEvaluator

Install important packages
npm install

Start the server
npm start

Testing

test npm test
test coverage npm run test:cover
test coverage in browser test:cover:browser

Test Plan

The use of ENTER will refer to entering an expression in the input
The use of EVALUATE will refer to processing the expression and obtain the value
The use of DISPLAY will refer to displaying the value
The use of ALERT will refer to alerting the user

Method Sequence	Expected Output	Actual Output
EVALUATE	ALERT "Please enter an expression"	ALERT "Please enter an expression"
ENTER "2 + 3" EVALUATE	DISPLAY "5"	DISPLAY "5"
ENTER "2+3 * 5" EVALUATE	DISPLAY "17"	DISPLAY "17"
ENTER "(32 - 5) * 6 + 3 / 2" EVALUATE	DISPLAY "163"	DISPLAY "163"
ENTER "3 / (6 - 2 * 3)" EVALUATE	ALERT "Cannot divide by zero."	ALERT "Cannot divide by zero."
ENTER "3 * 3 / 3 + 3 - 3" EVALUATE	DISPLAY "3"	DISPLAY "3"

UML Diagram

Lessons learned

In researching infix expressions, without reading the pseudo code provided, I was under the impression the ideal implementation would have been to use something called a 'read tree'. I thought through the process of making a tree, then went through the pseudo code for the infix evaluator. After the exercise, the process of using stacks feels less complicated for the expression evaluation.

Creating performant JavaScript using Arrays and Stacks has a few limitations. I almost created a class as an implementation over an Array to address the concerns I found. Instead, I used a few functions in a utility module.

Possible Improvements

I would like to add exponents and automated multiplication when a number is next to a group operator. Adding in factorial evaluation would also be an improvement. As far as the interface is concerned, adding a list of the past five or so expressions with their values would be great for recall and expression editing or mixing.