nw-fp-hexagonal-architecture

To separate domain logic from IO in functional programming, use a hexagonal architecture pattern with a pure core for side-effect-free domain operations and a thin shell for infrastructure. This enforces clear boundaries and keeps business logic independent from external systems.

A pure core and side-effect shell in hexagonal architecture define a pattern where domain logic remains side-effect-free, while infrastructure interactions occur through explicit ports as function types and adapters as concrete implementations connecting to IO.

Design ports as function types to define domain capabilities, and implement adapters as concrete implementations that connect with IO. Use environment-based dependency provisioning to achieve composable wiring of IO across typical app layers.

Yes, you can use hexagonal architecture patterns to improve testability in functional codebases by isolating side effects in adapters and keeping the core logic pure. This allows you to test domain capabilities without touching external infrastructure or IO.

The best way to wire inputs to outputs through pure steps is using pipeline-style composition. This hexagonal architecture pattern connects ports and adapters to perform end-to-end pipelines across typical app layers, ensuring clear boundaries and testability.