Effect TS App Patterns

Effect TS App Patterns

Overview

This skill is intentionally narrow. It does not try to teach all of Effect.

Use it for application-layer Effect code: route handlers, server functions, feature orchestration, async workflows, and business logic that benefits from typed errors and explicit execution boundaries.

It is not a full Effect reference. For broader APIs like Layer, Context, Schema, Stream, concurrency primitives, and service architecture, use the official docs linked in references/official-docs.md.

When To Use

• Converting Promise-heavy app logic into Effect
• Refactoring thrown errors into typed domain failures
• Writing multi-step server or feature workflows
• Adding logging and recovery inside an Effect program
• Standardizing where Effect.runPromise-style execution happens

Do not use this skill as a general “Effect best practices” guide for every module in the library. It is specifically about app patterns.

Default App Pattern

1. Model the program as Effect.Effect<Success, Error, Requirements>.
2. Use Effect.gen for multi-step orchestration.
3. Wrap unsafe sync/async boundaries with Effect.try / Effect.tryPromise.
4. Represent expected failures with Data.TaggedError.
5. Keep logs and recoveries inside the Effect pipeline.
6. Execute the program only at framework boundaries.

What To Read Next

• Read references/core-patterns.md for the preferred coding patterns this skill is built around.
• Read references/official-docs.md when the task needs Effect APIs outside this narrow app-pattern scope.

Common Mistakes

• Throwing raw exceptions for expected domain failures
• Calling Effect.runPromise deep in library helpers
• Using console.log instead of Effect.log* inside Effect-first code
• Hiding all failures behind one generic error type
• Reaching for advanced abstractions before basic effectful boundaries are clean