Reasoning about types is fun!

Today, I worked with Steve McCarthy on my Haskell game. We decided to implement a really simple feature: listing all the game files (files ending in "exp") in the current directory. I want to share how we tackled this problem because it shows a lot of the steps in learning how to reason about Haskell when you're a beginner.

( Lots of fun TDD and types behind the cut! )