Retail Store Discounts

On a retail website, the following discounts apply:

1. If the user is an employee of the store, he gets a 30% discount
2. If the user is an affiliate of the store, he gets a 10% discount
3. If the user has been a customer for over 2 years, he gets a 5% discount.
4. For every $100 on the bill, there would be a $ 5 discount (e.g. for $990, you get $ 45 as a discount).
5. The percentage based discounts do not apply on groceries.
6. A user can get only one of the percentage based discounts on a bill.

This is a simple application that demonstrates how you can code this in Python using Functional Programming.

Installation and Tests

Using guix

Simply load up the environment (for development purposes):

guix environment --load=guix.scm

Better yet, you could run a proper container:

guix environment -C --network --load=guix.scm

Running Tests

(assuming you are in a guix container; otherwise use venv!)

To run tests:

python -m unittest discover -v

Running pylint:

pylint *py tests app

Running mypy(type-checker):

mypy .

Running the flask app

To spin up the server:

env FLASK_DEBUG=1 FLASK_APP="main.py" flask run --port=8080

Using python-pip

IMPORTANT NOTE: I do not recommend using pip tools, use Guix instead

1. Prepare your system. You need to make you have python > 3.8, and the ability to install modules.
2. Create and enter your virtualenv:

virtualenv --python python3 venv
. venv/bin/activate

1. Install the required packages

# The --ignore-installed flag forces packages to
# get installed in the venv even if they existed 
# in the global env
pip install -r requirements.txt --ignore-installed

A note on dependencies

Make sure that the dependencies in the `requirements.txt` file match those in guix. To freeze dependencies:

# Consistent way to ensure you don't capture globally
# installed packages
pip freeze --path venv/lib/python3.8/site-packages > requirements.txt

Road Map

Port this to:

• [ ] Haskell
• [ ] Guile
• [ ] Rust

as some form as kata since it’s a simple enough exercise.