reverse-polish-suray

Reverse Polish Calculator

Overview

Technical Choices and Reasoning

Language Choice

Ruby was used for the following reasons:

• Ruby was a shared language between myself and the On-Site development team.
• The project was intended to be completed quickly, and therefore Ruby's dynamic typing, minimal syntax, and overall friendliness were complelling advantages in this context compared to a language like Java.

Operators as classes that include the Operator module

Advantages:

• Allows for additional operators by extension without modification.
• Allows for non default Ruby operators like ! for factorial.
• Allows for arbitrary association of symbols and mathmatical functions, for example sqrt could be mapped to Math.sqrt.

Disadvantages:

• Unncessary complexity for basic +, -, *, / operators, and additional default Ruby operators like **, %.

CircleCI

CircleCI was used in this project for these reasons:

• To automatically verify this project worked on machines other than my development machine.
• To automatically verify master has all of it's automated tests passing.
• To demonstrate some ability to work with modern CI/CD pipelines.

Docker

Docker was used in this project for these reasons:

• To attempt to make end user install and use as easy as possible.
• To make supporting a wide variety of user operating systems easier.
• To reduce potential for conflict between a user's environment and a developer's environment.

This decision has the following disadvantages:

• Potentially unecessary complexity and functionality.
• Potential for a broken docker container but a working Ruby program, or vice versa.

Known Issues

• This project was initially intended to be available as a Gem for other ruby projects to use, however this functionality was not completed and there are a number of currently useless files related to this, such as gemspec, version.rb, etc.
• The reverse/polish/suray/ file structure is currently overly nested, but is related to the initial goal of making the project available as a Gem.
• Running ruby bin/rpn_suray from the project root will cause unnecessary + is not a valid operator. error messages. This is due to a relative path issue in the Operator module. The project must be run from within the /bin/ folder, like ruby rpn_suray.
• A number of smaller issues exist that were not resolved due to time constraints. These can be found by looking for #TODO items in the project. Most of them do not affect end users, but can make the code unnecessarily difficult for developers to work with.

End-User Usage

Install and Run

Docker

Prerequisites:

• Docker

1. Enter docker run -it stevenuray/reverse-polish-suray:latest into a command line terminal.

Without Docker

Prerequisites:

• Ruby
• Git
• Bundler

1. git clone this repository to an appropriate folder on your local machine.
2. At the root of this repo's folder on your machine, bundle install.
3. Enter the /bin/ directory of this repo with a command line tool.
4. Enter ruby rpn_suray to run the program.

Example Use

Addition, integer numbers: 1 2 + > 3

Subtraction, decimal numbers: 3.14 2 - > 1.14

Multiplication, negative numbers: -3 2 * > -6

Division, repeating decimal numbers. 1 3 / > 0.3333333333

The answer from the last entry can also be used as the second number in the next entry.

1 2 + > 3 2 - - 1

Configuration

The following environment variables may be set by the user to override default settings:

• RPN_INPUT_SEPARATOR is the separator between numbers and operators. For example, changing it to "," would permit this entry 1,2,+. Default value is " ".
• RPN_DECIMAL_PRECISION is the maximum rounding precision for calculations. Default value is 10.
• RPN_EXIT_COMMANDS is a comma separated list of valid exit commands for the program. Default value is q,exit.

If you are using docker, remember that you need to pass in the environment variables to the container. An example: docker run -it -e RPN_INPUT_SEPARATOR="," -e RPN_DECIMAL_PRECISION=5 -e RPN_EXIT_COMMANDS="q,quit,exit" stevenuray/reverse-polish-suray:latest.

Developer Usage

Running Tests

At the repo's root folder on your local machine: rspec. Remember to ensure any environment variables you set to configure the application are unset when testing!

Creating/Use Development Docker Image

At the repo's root folder on your local machine:

1. Build image with: docker build -t 'rpn_development:latest' .
2. Run image with: docker run -it rpn_development:latest