A brief exploration of the various approaches to modeling side effects in a purely functional programming language.

Write a program that initializes an accumulator and random seed both with 0 and then runs the following procedure 10 times:

• Log the value of the accumulator.
• Pick an integer uniformly randomly from the half-open interval [0, 10).
• Mutate the accumulator by adding the random integer to it.

Thus, 3 computational effects are exhibited: logging, randomness, and mutable state.

This repository contains 4 implementations of the program described above, each demonstrating a specific technique:

• A bespoke monad
• A standard monad transformer stack
• A free monad
• The Eff monad from the "extensible effects" framework
• A Registry using the registry library

Make sure you have Make and Stack installed. Then you can use this command to run the demo:

make run