functional-core-imperative-shell

To separate pure business logic from side effects, move calculations into pure functions within a Functional Core and wrap I/O orchestration in a thin Imperative Shell, ensuring the core remains free of I/O for simplified testing.

The functional core imperative shell (FCIS) architecture isolates pure computations in a Functional Core and handles side-effect orchestration in an Imperative Shell, explicitly classifying files to prevent mixed concerns and reduce complexity.

To refactor an existing module, extract business rules into pure functions and create a minimal shell that handles file I/O and orchestration, enforcing strict separation to minimize drift and improve project maintenance.

Yes, the functional core imperative shell pattern applies to module refactoring by requiring explicit file classification with FCIS terminology, guiding architecture updates to isolate pure logic from side-effect code across software projects.

Enforcing strict file classification prevents mixed concerns and encourages a consistent project structure, ensuring the Functional Core remains free of I/O while the Imperative Shell handles orchestration to improve reliability.