FCIS Architect & Refactoring Guide FAQs

Question 1

Can I use logging in a Functional Core file?

Accepted Answer

Yes, logging is an explicitly permitted exception in this skill's implementation of FCIS, though it is recommended to pass no-op loggers during unit testing to maintain purity.

Question 2

How does this help with software testing?

Accepted Answer

By isolating business logic in pure functions within the Functional Core, you can write unit tests with simple assertions and zero mocks, making your test suite faster and more resilient to change.

Question 3

Why does this skill require file classification comments?

Accepted Answer

These comments act as a structural safeguard, forcing both the AI and the developer to consciously declare the purpose of a file, which prevents accidental mixing of logic and side-effects.

Question 4

When should I use the 'Mixed' pattern classification?

Accepted Answer

The 'Mixed' tag should only be used for existing code awaiting refactoring or rare performance-critical paths where separating I/O would cause unacceptable overhead, requiring specific technical justification.

Question 5

What is the Functional Core, Imperative Shell pattern?

Accepted Answer

It is an architectural pattern that separates pure, deterministic business logic (the Core) from impure operations like I/O, database queries, and API calls (the Shell) to improve maintainability.

FCIS Architect & Refactoring Guide

FCIS Architect & Refactoring Guide

Key Features

Use Cases

Key Features

Use Cases