The Functional Core, Imperative Shell Paradigm When To Use - Separating pure business logic from side effects - Improving testability through immutable domain models When NOT To Use - Performance-critical hot paths where immutability overhead matters - Purely imperative codebases with no plans to adopt functional patterns When to Employ This Paradigm - When business logic is entangled with I/O operations (e.g., database calls, HTTP requests), making tests brittle and slow. - When significant development time is spent rewriting adapters or dealing with framework churn. - When you require a sui…