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 ReaderTaskEither.
• You need functional backend architecture patterns rather than isolated utility snippets.

Core Concepts

ReaderTaskEither (RTE)

The ReaderTaskEither<R, E, A> type is the backbone of functional backend development:

• R (Reader): Dependencies/environment (database, config, logger)
• E (Either left): Error type
• A (Either right): Success value