How to write functional code in C#

Writing functional code in C# means the implementation of functional concepts and techniques that will help us write functional code:

• Expressions: By favoring expressions over statements, we can write more declarative code that focuses on the desired result rather than the steps to achieve it.
• Pure functions: A pure function always produces the same output for a given input and has no side effects. It relies solely on its input parameters and does not modify any external state. Using pure functions, we can create easier code to reason about, test, and parallelize.
• Honest functions: Honest functions are an extension of pure functions that provide a clear and unambiguous contract. They explicitly communicate their input requirements and potential output scenarios, including error cases. Honest functions enhance code readability, maintainability, and error handling.
• Higher-order functions: These functions can accept other functions...