fp-ts Backend Patterns Functional programming patterns for building type-safe, testable backend services using fp-ts. When to Use - You are building or refactoring a Node.js or Deno backend with fp-ts. - The task involves dependency injection, service composition, or typed backend errors with . - You need functional backend architecture patterns rather than isolated utility snippets. Core Concepts ReaderTaskEither (RTE) The type is the backbone of functional backend development: - R (Reader): Dependencies/environment (database, config, logger) - E (Either left): Error type - A (Either right):…