The Functions That Aren't Pure

In the functional programming paradigm, pure functions are ideal for code efficiency and reliability, but in reality, many applications can't achieve 100% purity due to external factors like persistence, user input, or network data access. Pure functions always produce the same output given the same inputs, without side effects such as modifying external state or accessing external resources. Impure functions have side effects that can lead to bugs and make testing more complex. While pure functions are ideal, a mix of pure and impure functions is often necessary in real-world applications, and being aware of purity/impurity helps with application testing and debugging.