Functional Core, Imperative Shell

• As the name suggests the core domain logic of the software should be functional. It must rely on immutable values and pure functions.
• The shell can be programmed in an imperative style. It will take care of all the side effects like making and responding to network requests.
• The shell can call the core but not the other way around.

Resources

• Functional Core, Imperative Shell - Destroy All Software #media/video
• The Functional Core, Imperative Shell Pattern – Kenneth Lange #media/article