This is an ESLint plugin (`eslint-plugin-functional`) that enforces functional programming patterns in JavaScript and TypeScript code. It provides 20 actively maintained rules targeting immutability, functional parameters, no classes, no exceptions, no statements, and other FP principles. The plugin deeply integrates with TypeScript's type system via `@typescript-eslint/utils` and libraries like `is-immutable-type` for type-aware immutability checks. It offers multiple configuration presets (strict, recommended, lite, etc.) and supports ESLint 9 and 10 flat configs. The codebase is well-structured with a consistent rule factory (`createRule`), shared utilities (type guards, option overrides), and an extensive test suite using snapshot testing. It is actively maintained with frequent releases, a comprehensive CI pipeline, and semantic versioning.